Fitting low water pick up to outboard engine

[phillnjack]

High folks
something ive never done and never seen in the flesh is a low water pick up for outboards.

Im seriously thinking about raising my engine up around 4 to 5 inches to ride on the bullet or close to the
bullet and dont know exactly how or where to make the low water pick up. ?

Any advice or ideas including pics would be very good for me, i have a few ideas but probably totaly wrong.

I was thinking about a transom mounted pipe with a slash cut to force water up when on the move,
but will this work at slow speed ?

The impellor is a lot lower in the water than a transom mount would be at slow speed and not sure if it would prime itself etc.
is it best to fit one on the lower part of the gearbox at the front of the bullet ?
my engine is a 56ci omc with normal gearbox not a racing gearbox, and realy dont want to change it.

Also are nose cones the way to go, and do they realy just stick on with epoxy and stay put ?


any advice will be good




phill..:cool:

[Fast Fred]

welded on, an SST 60 foot is the stock go fast set up for that Moda, heard someware that a Fast Fred Nitro foot is hot, that would fit.... thinkin there's a shot on hear ....

[phillnjack]

I dont want to change the gearbox.
I want to keep the same gearbox and just put a low water pick up on it.
I like the nosecone type of thing sold by bobs machine shop, but thought it very strange that
it comes with epoxy to STICK it on.
dont think i would trust a stuck on cone, but welded on yes, maybe they mean tack welded an the
epoxy is just for finnishing and smoothing off ?.

but i need to know a bit more about what i have to do to the original holes and where to drill etc.
spme pics of anyone work they have dont to make this would be very good..


phill

[byrdsperformance@tds.net]

I had a friend that decided to remove his nosecone it was bonded only by the epoxy kit inculed with kit.
He chiseled, cut. beat an cussed a long time. Some notching an fitting is needed to fit various cases.
Once a proper fit an aligmnent are achived you can tack weld then bond.

[LittleCharger]

Where is the bullet relative to the bottom (pad) of the boat now? Seeing that you want to raise it 4 to 5 inches now it's pretty buried. I would invest in a water pressure gauge and raise the motor to see if the boat reacts to your liking. You should be able to raise the motor such that the center of the bullet is 2 to 2.5 inches below the pad and still have plenty of water pressure even without the low water pick up. Do you have access to surface piercing props to run when you raise the motor? Not all props liked to be surfaced.

Cheers,

[phillnjack]

at the moment the centre of bullet is about 5 to 6 inches below the lowest point of transom.
My engine is a longshaft, normal 20 inch transom on the boat, (actualy 20.5 inch.)
I cannot raise anymore untill a jack plate is fabricated to what is gonna happen to handling etc.
I will be using the boat for different things,so an adjustable plate will be need so i can run deep when at sea in
rougher water at a reasonable pace.
water pressure guage is a good idea and was thinking about ptting a fitting on the exhaust plate where there
is a plugged off area with allen screw in it.
(not sure if this is a good place, but got to be better than putting a tee in the pee hole as would be getting a
true pressure reading of whats comming from the water pump)

quote
"You should be able to raise the motor such that the center of the bullet is 2 to 2.5 inches below the pad
and still have plenty of water pressure even without the low water pick up."

centre of bullet is 7 inches from cav plate so to get bullet 2 inch below boat bottom would need the engine rasie by 5 inches.
I honestly dont think ill get any water at that height, the water pick ups are a few inches above the bullet !!!!!



phill

[sharpeye Mike]

Phil, the sst60 foot does not have bottom pickup and they do just find, I run my 15" nitro case with the two top pickup holes block off at 21.5" high and I have no water pressure issue. Get a water press. gauge, tee it in the pee hose inside the cowl for reassurance. Raising the motor 5" wont be a problem, find a good prop and you're good to go.
Mike

[phillnjack]

I shall have to get a jack plate and a guage and give it a try.
but i realy dont think ill get enough water.

when i tried a little 4hp merc on the back of my boat it didnt get enough water and that is a 15 inch shaft.
but i shall give it a try and see what happens.
i was under the impression that a nosecone would also give better performance , but if not gonna gain it might not be
worth doing.
I just fancied giving a few little extra bits of performance .

Now being as the engine will have gone back by 4 inches when i fit a jack plate how far from the bottom of the boat should the bullet be then.

The way im reading this is the engine needs to have the bullet just 2 inches lower than the pad.
So if the boat was a 23/24 inch transom i would be fine.
But using a set plate /jack plat that goes back another 4 inches, does the engine need to be even higher ?
if so with 4 inches of set back what height should the bullet now be ?
should it be 2 inches higher than bottom of boat, or about centre of bullet level with bottom of boat.

this does seem to be extremely high to me.


phill.......

[sharpeye Mike]

From what I understand, you are doing all this to a 13' Boston Whaler type of boat. Not all small boats like set back, I would start with the shortess setback you can find and raise the motor 5", then you can raise it or lower it at will.
P.S. While you're at it change the water pump.
Mike

[phillnjack]

why water pump change ?
what would be a better water pump ?
never knew about different water pumps, i thought the high volume pump on this engine would be fine ????

Without some form of setback its not gonna be possible to raise the transom height.
unlike a normal speedboat you cannot get to the transom woodwork to beef it up.
The only way to rais eit would be to use metal plates with a wooden insert that would
be very heavy on the rear end.
Or if i had a stanless hollow block made up for it to try and keep weight down to minimum.
thats why i was opting for a setback jack plate type thing.



phill

[sharpeye Mike]

Sorry Phil, I ment the impeller in your water pump, just a precaution, they do wear out.
Mike

[phillnjack]

you wouldnt believe how strict i am with impellors.
i had a engine back in the 1980's that had done 2 hours on a brand new impellor and the impellor went bad.
the engine siezed up and was totaly destroyed.
Every couple of runs i whip the legs off to just make sure the impellor housing is clear of any rubbish and check the blades.
I dont trust any impellors, new or old.
On a friends johnson 140 recently i took the leg off, his impellor looked like brand new.
But on close inspection i noticed the impellor was NOT stuck to the hub !!!!!!!!!
it was totaly useless and was the cause of no water getting to the powerhead.
That impellor was brand new...
pic below of the bad impellor, so anyone reading this make sure you do a proper thorough check on them.
this looked fine, but the rubber stayed static when the shaft was turning !!!!!!!!!

51861

this the impellor when taken off the shaft !!!!!!!!
Notice the rubber had only a tiny touch of glue from new !!! this was OMC original part, not a cheap copy.
51872
.



phill

[Fastjeff57]

Been messing with OBs for half a century and never saw that one before!

Jeff

PS: One if my inboard guys SWEARS that he ran the same impellers in both engines for eleven years without a problem, and only changed them 'cause he felt it was "time"!

[sharpeye Mike]

I second that Jeff, a water press. gauge is still a cheap insurance and yes the oldess impellor I replaced was 11 years old, the vanes where cracked and bent backward.
Mike

[phillnjack]

ive never seen this myself before neither, but have since spoke to a few people who have seen this happen.
And it seems a lot of jabsco pumps have had this happen as well as volvo penta and mercury.

Its obviosly poor vulcanising at the factory, and if you notice the hub is smooth not a pimpled or rough surface
like you would expect it to be.
The new ones that have a plastic hub seem to be more of a melted rubber into the plastic feel about them.

Anyway as soon as we changed the impellor the water pressure to the motor was great .

i told a few people about this on scream and fly and on iboats, people there have had this happen before.
so its not like its one of a kind.

apparantly a lot of this happened during the 1990's with many different brands of impellor, maybe there was a
dramatic change in how the vulcanising was done that caused such things to happen.

probably something cheap was tried by whoever realy made all the impellors for the different company's. ?



phill

[phillnjack]

about how long they normally last is probably due to how many hours you run.
now in the uk most boats are used in salt water, and its not the nice clear warm stuff you se in florida of california.
In the uk you could not have an impellor for 11 years unless you kept the engine in the attic and never used it.
even then it would have a set and be useless. ha ha


phill

[chris3298]

[QUOTE=phillnjack;127952]about how long they normally last is probably due to how many hours you run.
now in the uk most boats are used in salt water, and its not the nice clear warm stuff you se in florida of california.
In the uk you could not have an impellor for 11 years unless you kept the engine in the attic and never used it.
even then it would have a set and be useless. ha ha

I'm very religious on flushing my motor with some stuff called Salt-Away, whether I run in salt or fresh water I always use this tuff. I had a 15 hp Evinrude handed down to me and it was really bad about clogging up but once I started using Salt-Away I really never had problems again. I sound salesman but no really it worked great. I've heard of people flushing there motor with vinegar but have been hesitant on that one. I would assume this stuff may help the rubber seals maybe from cracking up but still is no excuse to use it to not change an impeller....

[phillnjack]

sharpeye mike
ive just re-read your statement above about how you run your engine.
you say its 15 inch midsection on a 21.5 transom and you get plenty of water ???????
thats 6.5 inches up...you must be using a setback of some sort.
if you bolt the engine direct to the boat at 6.5 inches up the transom, then on plane you shouldnt get enough
water up that high to cool the engine, and with the longer sharper bullet it should be riding with bullet above the water.

i cannot see how your getting anything over the water intakes at all without a setback..



phill

[LittleCharger]

sharpeye mike
ive just re-read your statement above about how you run your engine.
you say its 15 inch midsection on a 21.5 transom and you get plenty of water ???????
thats 6.5 inches up...you must be using a setback of some sort.
if you bolt the engine direct to the boat at 6.5 inches up the transom, then on plane you shouldnt get enough
water up that high to cool the engine, and with the longer sharper bullet it should be riding with bullet above the water.

i cannot see how your getting anything over the water intakes at all without a setback..

phill

The centre of Mike's bullet will still be below the pad at that measurement (i think probably around 2"). You need to consider the additional depth the lower unit adds to your equation, the 15 inches is only the mid section. Perhaps Mike can post a picture of his set up and I think that will makes things a little more clear. The 21.5 inches is measured from the bottom of the pad to the U part of the clamp bracket that traditionally sits on the back of the boat.

[calvin]

I ran a 15 inch 3 cyl on a critchfield....22 inch transom..pumped fine ..why...?

[thornl01]

Seen this happen a few times since I started work on outboards, (1973). the failures usually don't care if they are OEM or Aftermarket. I have Used Both & have no opinion as to which is better now. Just nees to be sure that impeler is lubed liberally at installation & to minimize the dry " engine starts & simple spinovers". QC is just not what it used to be.

Lawrence Thornton
South Carolina Mellon Belly Associate.

[Per]

sharpeye mike
ive just re-read your statement above about how you run your engine.
you say its 15 inch midsection on a 21.5 transom and you get plenty of water ???????
thats 6.5 inches up...you must be using a setback of some sort.
if you bolt the engine direct to the boat at 6.5 inches up the transom, then on plane you shouldnt get enough
water up that high to cool the engine, and with the longer sharper bullet it should be riding with bullet above the water.

i cannot see how your getting anything over the water intakes at all without a setback..



phill


There are several interesting movies on youtube showing surfaced gercases, you will be surprised how high the water "climbs" or get pushed up. Normally you see a lot of spray comming from beneth the Anti ventilation plate, a good sign that the water has climbed past the std water inlet. Some people plug the upper intake holes that might be a good idea...

[sharpeye Mike]

51902

Not sure if this work but if this pic. comes out you will be able to see how high we run these motors with no water issues and yes I block off the tree top holes and I drill out the tiny drain hole. I gained 3 lbs. of water pressure with this mod.
Mike

[phillnjack]

hold on a moment
the centre of bullet is 2 inch below the bottom of the boat, yeah i get that bit.
Now my gearcase is 4 inch and bit, so if i ran with the centre of bullet 2 inch below then the top of
the bullet would be level with the water when on plane.
Now the lowest hole on my engine is around 3.5 inch above the centre of bullet.

in the pic below i have put a red line on the centre of the bullet.
the yellow line is what sharpeye mike must have as a minimum water line.
the green line is roughly where my water line is when on full throttle with the engine raised up to
top bolt hole at the moment.

this is why i am saying there is no way i can raise 5 inches and still get water, it would be impossible without the
engine going back a long way.
At full throttle about the last foot of the boat is all thats in the water and its very skittish and light on the arse end
when trying to keep it in a straight line..
.
51903


phill

[chris3298]

hold on a moment
the centre of bullet is 2 inch below the bottom of the boat, yeah i get that bit.
Now my gearcase is 4 inch and bit, so if i ran with the centre of bullet 2 inch below then the top of
the bullet would be level with the water when on plane.
Now the lowest hole on my engine is around 3.5 inch above the centre of bullet.

in the pic below i have put a red line on the centre of the bullet.
the yellow line is what sharpeye mike must have as a minimum water line.
the green line is roughly where my water line is when on full throttle with the engine raised up to
top bolt hole at the moment.

this is why i am saying there is no way i can raise 5 inches and still get water, it would be impossible without the
engine going back a long way.
At full throttle about the last foot of the boat is all thats in the water and its very skittish and light on the arse end
when trying to keep it in a straight line..
.
51903


phill

In the picture my water line is about where the yellow line is or I should say the bottom of the boat is where the yellow line is, now I'm running a hi-jacker jack plate with 6 inches of setback. I've got my motor jacked up all the way and I think I may have to drill some holes in the jack plate to go up a spec higher. I had to have some cup added to the prop so it wouldn't cavitate so bad. I've run it raised all the way up but winter hit here and it's to cold to try the boat out with cup being added and the motor raised all the way up. I can say with no cup added and motor raised all the way up using a water pressure gauge the gauge would fluctuate a little but once on a plane it would have dam good water pressure.

Still testing and would love to get back out there but gotta wait for it to warm up. I was actually able to see what the water is doing as it goes around my lower unit and must say it's pretty cool to watch. I have just the stock side water pickup and NO low water pickup like what Bobs machine sells.
Where your red line is the water on my motor will hit the nose cone area just about an inch above the redline in your picture and the water then sprays up to or just above the yellow line. From your pictures I use to think the same dang thing but until I actually seen it with my own eyes how the water is traveling it really is pretty cool to watch but don't watch to long you'll be on the bank ;) amazing how high they can be jacked with no lwp but the motor I'm gonna be building this winter will have a lwp

[Fastjeff57]

I'm with "Per" on this one. The water flowing out from under the stern shoots upward immediately and "is there" when the motor needs it.

Jeff

[chris3298]

Good drawing Jeff I thought how could I do this but I have a hard enough time just posting a picture.

[Glenno]

Hi all,

Sory I didnt catch this thread earlier, I love talking nose cones!

Phill, I really think you would be fine just to make a two part filler nose cone. I race the 25hp and 550cc super sport outboard here in Australia and have run a full two part filler nose cone for five years now (raced it hard with no probs). The reason for low pick ups is if you wanted to get the torpedo level with water surface or above (like my 550cc- runing 1/2 inch above water) when at full go.

I have gone to the trouble of adding low pick ups to motors before and found it to be a bit of a waist of time as a filler nose cone seems to to the job of pulling the water up to the factory pick ups just fine.
All the guys here that race run a tube from the factory tell tale up to where they can see it (beside them) to make sure the motor has water.

http://www.youtube.com/watch?v=7YX_8nEaJqA&feature=player_detailpage

I hope thats some footage of my nose cone when we where testing, it runs hiegher now ans still feeds water with factory pick ups, see how the cone pulls water up the gear case.

[phillnjack]

Good video and very good picture.
I can see what everyone is saying about the engine running in water that is comming up from the transom.
But everyone also seems to be running with atleast 6 inches of setback !!!!
with a setback yes the water level will be higher due to the water returning back to its original level.

Also in the pick above the nosecone is pointing down, its definitely not running parallel to the drive shaft,is this
for a reason ?

can you tell me what benefits you have found by using a nosecone , ive never used one but realy like the look.
do they realy give a noticable performance gain ???


phill

[Fastjeff57]

Gotta admit, they look cool! As I understand it, below 60 mph or so they don't do much. Furthermore, the Yamatos never used a 'bullet' and are certainly competitive.

Jeff

[Glenno]

Hi Jeoff,

Yeah I noticed a massive diference in a number of ways.

1) without the nose cone I would never be able to run the motor as high as i do and still pick up water (our rules dont allow us to change the factory pick ups) , thats part of the reason the my cone drops lower than centre of prop shaft by 1/2inch to pull more water up, you do need to be carfull doing that though as one of my mates went to far and caused his boat to poupus, he re-shaped and works sweet.

2) I did take the boat out once without the nose cone and experienced bad blow out (if thats where you cant steer and feel where the motor is tracking), I found that the nose cone extends the torpedo of the gear case and helps it to track better, also a little kick on the right trailing edge of the skeg for right turn prop motors helps overcome tourque steer. I will attach a pick, look at the back edge of the skeg-not the best pick.

3) One test day I raised the motor just a 1/4 of an inch and gained 3.75mph.

I here what Geff is saying about under 60mph they dont do much and do agree with him for some boats but with all respect to him I have to disagree as it really depends on the boat, total weight of the rig, how high you want to run your motor and what you are trying to achieve - I am even chasing 1/4mph as that can win a race. I have to agree with Geff again, They do look cool! and I cant resist adding a nose cone to most outboards i have owned - even fishing motors.
Some picks of other cones I have made- The second pick is the one to look at for the kick on the skeg.

[Glenno]

Hi again,

I forgot to say in regard to set back- a lot of the guys running in the mono hulls at our club have no set back at all and are running the centre of the prop shaft in line with the bottom of the hull (running plank), But like i said earlier we all run our water tell tales up to where we can see to make sure the motor has water.

Looking at your water pick ups I would start with your motor 2 inch below bottom of hull to the centre of prop shaft if you had a nose cone and work up from there and make sure all the time you have water, water, water all the time. You would definately want a different prop, the props with the converging ring at the trailing edge of the hub are like a brake, I attached a pick of a prop I rewoked and put a bell on trailing edge instead of converging ring, and a few more picks I found of nose cones I have done.

Hope this helps
Glenno

[tsrt]

51967 easiest way

[tsrt]

easiest way51968

[phillnjack]

well now im beginning to think the nose cone is a silly idea.
from what you say, the cone is there to get the gearbox to dig under the little bit of water left and shoot it up the shaft.

other people tell me they fit the cones to help the gearbox get on Top of the water and keep water underneath
the bullet to let it ride on top of the water .
so either its for gaining speed by getting the bullet out the water, or losing speed slightly due to digging under the water to make it meet the stock intakes.

it cant be doing both things right and both ways gaining speed, is it quicker or slower !!!!!!


phill

[chris3298]

This is a good video but you have to turn your head or laptop side ways http://www.youtube.com/watch?v=WIXvi33I0o8 he is running a nose cone and actually has a piece of tubing on the transom to suck up water. This guy has said he runs his motor higher up the what a lwp would do. This is a good video to see whats going on.

[phillnjack]

well in the video above he is not that high at all.
he is only running with the cav plate about 2 inches above the water.

he says he is running 3.75 up, but being as he is using a jack plate as well ,he is only about 1 inch higher than me.
mine is running with the cav plate above water line and im just on the top hole with no jack plate and no setback.

he is nowhere near running on the cone, so i dont see how he could lose water pressure.
The bullet on his engine is completely submerged, not even a glimps of it.

I noticed he has a nosecone, and it looks like they make a realy big splash, a lot more than the normal bullet.

so whats the advantage of these cones ? im begginning to think they are just a gimic that dont realy work.
if they cause the water to go up the gearcase and away from the prop then they are obviously diverting water away from the prop .
this would mean less thrust due to less water at the prop.
If they are helping to raise the engine then they would not help with water flow due to the cone pressing down on the water. !!!!!!!!!!!

now the vid above shows a jack plate with setback,nosecone, and a hydrofoil and he still only gets 70mph on
a 13ft lightweight raceboat with a 130hp engine.

something dont sound right, how comke all these race improvements yet not much speed.
I could get that on my dory with 130hp engine let alone a racing boat.


phill

[89HST]

well in the video above he is not that high at all.
he is only running with the cav plate about 2 inches above the water.

he says he is running 3.75 up, but being as he is using a jack plate as well ,he is only about 1 inch higher than me.
mine is running with the cav plate above water line and im just on the top hole with no jack plate and no setback.

he is nowhere near running on the cone, so i dont see how he could lose water pressure.
The bullet on his engine is completely submerged, not even a glimps of it.

I noticed he has a nosecone, and it looks like they make a realy big splash, a lot more than the normal bullet.

so whats the advantage of these cones ? im begginning to think they are just a gimic that dont realy work.
if they cause the water to go up the gearcase and away from the prop then they are obviously diverting water away from the prop .
this would mean less thrust due to less water at the prop.
If they are helping to raise the engine then they would not help with water flow due to the cone pressing down on the water. !!!!!!!!!!!

now the vid above shows a jack plate with setback,nosecone, and a hydrofoil and he still only gets 70mph on
a 13ft lightweight raceboat with a 130hp engine.

something dont sound right, how comke all these race improvements yet not much speed.
I could get that on my dory with 130hp engine let alone a racing boat.


phill


You might want to put some spectecles on and watch the video again :rolleyes:

[Krazy Karl]

Gotta admit, they look cool! As I understand it, below 60 mph or so they don't do much. Furthermore, the Yamatos never used a 'bullet' and are certainly competitive.

Jeff

Most of the guys do shape the Yamato gear cases but we aren't allowed to add a bullet in stock, however in Mod we can. This is what is usually done. I found it makes for quicker turn in on the corners.
51970

kk

[Glenno]

Hi all,

I definately dont run extra pick ups, I would be disqualified, the scruteneers would see it strait away.

yes the cone is to pick water up but the speed is gained by reducing the amount of gear case that runs through the water (dont think of it digging down) and also getting the prop to surface pierce. If you can get the prop to run 1/2 out of the water you can run a much heigher pitch wich usualy = more speed.

Glenno

[phillnjack]

well the half out the water = more speed is not exactly correct !!!!!!!!!

The larger pitch is requiered simply becase the propeller is not fully in the water.
if 30% of the prop is not in the water then its not being used to propel the boat in forward motion,so obviously it would require more pitch on the remaining blades to keep the speed up.

i did have another look at the video and yes i was wrong the bullet is out the water sorry about that.
at one point the cone is not in use at all !!!!!


phill

[Per]

well the half out the water = more speed is not exactly correct !!!!!!!!!

The larger pitch is requiered simply becase the propeller is not fully in the water.
if 30% of the prop is not in the water then its not being used to propel the boat in forward motion,so obviously it would require more pitch on the remaining blades to keep the speed up.

i did have another look at the video and yes i was wrong the bullet is out the water sorry about that.
at one point the cone is not in use at all !!!!!


phill

"Half out= more speed" is true under the right circumstances. With a prop designed for it you cut your losses and thereby win speed:)

[phillnjack]

ask any prop maker and he will explain it to you.
the only blades working are those in the water at any given time.



phill

[chris3298]

well in the video above he is not that high at all.
he is only running with the cav plate about 2 inches above the water.

he says he is running 3.75 up, but being as he is using a jack plate as well ,he is only about 1 inch higher than me.
mine is running with the cav plate above water line and im just on the top hole with no jack plate and no setback.

he is nowhere near running on the cone, so i dont see how he could lose water pressure.
The bullet on his engine is completely submerged, not even a glimps of it.

I noticed he has a nosecone, and it looks like they make a realy big splash, a lot more than the normal bullet.

so whats the advantage of these cones ? im begginning to think they are just a gimic that dont realy work.
if they cause the water to go up the gearcase and away from the prop then they are obviously diverting water away from the prop .
this would mean less thrust due to less water at the prop.
If they are helping to raise the engine then they would not help with water flow due to the cone pressing down on the water. !!!!!!!!!!!

now the vid above shows a jack plate with setback,nosecone, and a hydrofoil and he still only gets 70mph on
a 13ft lightweight raceboat with a 130hp engine.

something dont sound right, how comke all these race improvements yet not much speed.
I could get that on my dory with 130hp engine let alone a racing boat.


phill


no not 70 this guy is running a little over 82 mph. Do a search on here and you will see more pictures of that 13foot biel and that motor is actually a stock 130 yamaha.

[phillnjack]

if you go on youtube and see his video's you can see its not stock.
he has a different leg to normal stock motor and a tube running to the transom for water.
that is not stock,plus jack plate and a nosecone.

its ok to say its a stock motor, But its not stock on the outside.
This guy has spent best part of $1,000 already on mods for the engine.


phill

[chris3298]

if you go on youtube and see his video's you can see its not stock.
he has a different leg to normal stock motor and a tube running to the transom for water.
that is not stock,plus jack plate and a nosecone.

its ok to say its a stock motor, But its not stock on the outside.
This guy has spent best part of $1,000 already on mods for the engine.


phill


Sorry what I meant stock was I think he had said there is no performance mod to increase horse power to the powerhead itself but yes that lower unit I guess is considered a performance mod.

Here's the link to more pictures man I wish I had the money to own this boat they sure do look like fun http://www.boatracingfacts.com/forums/showthread.php?12011-13-Biel-Tunnel-with-Yamaha-130&highlight=Biel+13foot

[Fast Fred]

from 3 o'clock to 6-6:30 is the thrust and or push the rest is Drag, thats from 6-6:30 back around to 3 0'clock = drag, when you surface the prop you unload the drag. don't work on every hull

[phillnjack]

so whats happening between 6 and 9 ?
i realy cannot see that being right.
there is no difference between 6 to 9 to cause a drag effect.

have you got any proof of this ? or is this just your opinion on the thrust v drag of prop blades ?


phill.........

[Fast Fred]

well, see if can get you there with words, the deeper you go the more weight water has, the opposite it true as well, yes, you with me, at 6-6:30 the blade is now turnnin into lighter water, the next blade is now turnnin in and down it is now pullin harder than the blade leavin the water, at the point that the incomin blade over powers the outgoin blade,
at that point the out goin is drag, cuzz it's in the way

[phillnjack]

who told you that water gets heavier the deeper down it is ? they dont understand H2o to even think about that.
Do you think a diver can swim faster at 10 feet than he can at 30 feet with the same amount of bouyancy ?

Yes there is more water Pressure the deeper you go, but this realy dont even start to be
measurable untill 15 inches down.
In the first 12 inches of water, the pressure is still the same as atmospheric pressure,roughly between
14.7 and 15 psi depending on where you live.obviously high or extreme altitudes are not the same

I dont think i could ever be convinced about the 3 to 6 thrust and 6 to 9 all being drag.



phill...

[phillnjack]

I am trying to find something about the blade causing drag but not getting any info from anywhere else.

is there somewhere i can find proof of this to be true ?


phill

[88workcar]

Mr Phil, you keep asking questions. That means that you do not know every thing. So why do you argue with every answer that is given to you? There are many very experianced people here that are tring to help you. Try to listen, just a little.

[89HST]

I am trying to find something about the blade causing drag but not getting any info from anywhere else.

is there somewhere i can find proof of this to be true ?


phill

No it's not true, thats why Mercury spent millions over the last 60 years on lower unit and propeller technology, not to mention all of the aftermarket support of nose cones and prop makers. All the pictures you see of Champ/F1 boats are merely photoshoped to make them look cool, the new video posted of the F60 is smoke and mirrors. :rolleyes:

[Fast Fred]

to test out the ideas said, usein a hull with the "sweet spot" in the center hole, ( sweet spot is the best all-around hole on the transom, not to high not to low)
( usein the center hole so to test one up and one hole down from center) stay with me, based on the prop drag idea, if we drop down,one hole,(deeper) the hull is slower, she may not make max rpm, lugin it. one up from center, she may be faster top end, but she blows out, over revs, lightin the limiter:cool: these would be the outcome of this test............:cool:

[Bill Van Steenwyk]

I am trying to find something about the blade causing drag but not getting any info from anywhere else.

is there somewhere i can find proof of this to be true ?


phill



Lets pretend the prop has NO FUNCTION as far as propelling the boat thru the water, other than the fact it is there in it's normal location, on the prop shaft, and in the water. In this visualization, propulsion is being achieved in this example by ANY other means you might imagine EXCEPT the propeller. Could be water pump, sail, oars, or any other type power that will move the boat forward through the water EXCEPT that prop on the motor.

Now imagine it raised on the transom so only a part of one blade is in the water at any one time.

Now imagine it lowered on the transom so ALL of the blades on the prop are completely submerged in the water at one time.

Which location of the prop (depth in the water) do you think will give you the best speed, all other factors remaining the same.

Same thing applies when the prop is driven by an engine and that prop is the sole propulsion for the boat. The more blades in the water, the more DRAG. It also may be easier to imagine the prop as a complete disk. The bigger the disk the more drag. If the disk has holes or slots cut into it, drag will be reduced. That is also the reason a jet airplane is faster (among others) is an airplane with a propeller generates much more drag than one without. Add more propellers (think 4-6 engine bombers) and more drag. In addition, the tips of the propeller reach supersonic velocity while the vehicle itself is much below the speed of sound, also leading to propeller inefficiency. That and drag is why a prop jet is slower than a pure jet.

There is much more to it than just this, just as air is much different than water insofar as the way it acts when moving through it with a propeller or any other object,and that is where number of blades, pitch, diameter and other factors enter into the equation. BUT one of the large things to effect a prop (or any other object moving thru air or water) is DRAG. This is also the reason that some still run props with only two blades when racing, although not a lot anymore. If water conditions will permit, a two blade will probably be faster (taking into a lot of other factors) than a multi blade prop, especially when you are running a surfacing type prop, is there is LESS DRAG with 2 blades than 3 or more. This is not always true, depending on handling problems you might encounter in rough water, etc. You can raise a multi blade prop higher out of the water and have the boat have better handling capabilities because of that word again, DRAG. Eventually you get to a point where handling and prop efficiency become more important than drag reduction, especially if you can not control the boat anymore because of lack of directional control which the lower unit/prop combination in the water give you.

Unfortunately there is no magic formula which will allow you to calculate this point. The only formula is testing and good record keeping.

Hope this helps.

[chris3298]

I have to agree with Jason/88workcar these people here know so freaking much it's not even funny, some more then others. Like fast fred said go experiment if you don't believe.

[Fastjeff57]

Hey, Bill: If your theory is correct, then why the advent of 3, 4 and 5 bladed race props when TWO (by your theory) would be far better?

Jeff

[phillnjack]

No i would not believe someone trying to tell me that the water within range of a raceboats prop is heavier at the bottom than top.
Anyone thinking this would be realy thick and shouldnt be allowed near machinery.

Now just because someone has something that works perfectly and does what they wanted it to do when they first invented it,dont mean they know how it works scientifically.
That we only have to look at the wright brothers to see what i mean about that.
Although they got mans first flight in a aeroplane to work,it wasnt the way they thought it was that actually got the plane off the ground.


Now then comes the nice long theory by Bill van steenwyk
he wrote
"Now imagine it lowered on the transom so ALL of the blades on the prop are completely submerged in the water at one time. Which location of the prop (depth in the water) do you think will give you the best speed, all other factors remaining the same. "


well to answer this one would look at a torpeedo or submarine.
The only place where the prop is not as efficient is where its attached to the torpeedo or submarine.
If this is just attached through the hub and no skeg or fin to disturb waterflow then the prop is efficient 360 degrees
of its travel..


I can understand that surface props are made a certain way to cut into the water at surface, and probably a lot more going on than just that at that moment.
But once the blade is submerged its trying to pull itself through the water.

It would be exactly the same if it was trying to pull through a solid medium.

With surface i can see the prop is basically doing nothing for 50% of the time if the bullet is level with the water.
And i can see there is going to be a touch of water slippage at the point of the skeg.
But for the prop not to be pulling at the 6 to 9 oclock does not seem right and no reasonable explanation for this.
the water is no different between 6 to 9 than 3 to 6 other than it will have a drop of air with it carried in with it by the blade out the water.now that blade to me is obviosly not working as hard as the one thats lost its air !!!!!!!!!!!!.
so therefore the blade from the 6 to 9 would infact be the one pulling harder if anything !!!

For those that dont like answers being questioned then i suggest you get a life and dont just be sheep.
Yes i am argumentative, and thats my perogative , as i want to find out the true answers to things not just accept anything told by someone else who dont realy know the answer.

without questing things we would never get any improvements in anything at all let alone props.
the Prop shop shop experts are allways comming up with new improved props to give better performance.
so they too must be questioning the effects of blades in the water and how they are realy working.

I thought the whole idea of a forum was to get answers and have debates to find out a lot more on the practical and the theory of the workings of boats engines and propellers.
if this is not the case then i shall just sit and read and wont bother asking anything.


phill

[chris3298]

Phill I guess you have a point there.

[byrdsperformance@tds.net]

Phill'
At one time quicksilver by mercury had a book. I think it was called ALL YOU NEED ABOUT A PROPPLER.
If you can find one of these it's a help.

[ima75man]

if 100 hundred people witness a car wreck, you would have 100 hundred different answer to what happen. lots of people draw outside of the lines, don't mean they wrong, do whatever that works for you.

[Bill Van Steenwyk]

Hey, Bill: If your theory is correct, then why the advent of 3, 4 and 5 bladed race props when TWO (by your theory) would be far better?

Jeff





Jeff:

Did NOT say it was ALWAYS correct about 2 blades, but the main reason outboard powered hydroplanes went to multi-bladed props in the late 60's was for controllability reasons, not speed. You could run less lower unit in the water and still maintain control and speed better in rough water or a turn than with a two blade prop.
Look at Drag boat propellers, that only run in a straight line.


Phillnjack:

Think you are missing the point. Go back and read the FIRST paragraph of my post again. Why do you think that tunnel boats experimented with "water brakes" at one time, consisting of rods that came down into the water from above the planing surface of the boat. The reason is DRAG, in that case to slow the boat quickly before entry to the turn.

Most everybody on this forum likes and enjoys a lively discussion, but I can certainly understand why someone might take offense at being called "thick minded" when they are trying to answer your questions to the best of their ability.
After all, they took the trouble to try to help YOU, with a question YOU asked, in a very civil manner.

My answers to your question are based on 40 years of racing experience, as well as others who have tried to help you. If you do not want to avail yourself of that experience, then don't ask for help. We may be right, we may be wrong, but insulting our answers to your questions does nothing for our willingness to try to further answer them.

[Krazy Karl]

Since I started boat racing I have always pondered the dynamics of the propeller. I can understand the 3 to 6 idea and the loss on the 6 to 9 quadrant, but I never looked at it as drag. I see where that could be a very definite factor and it makes sense as the in coming blade is pushing harder. I always looked at it that the blade going into water is pushing against the whole body of water below the blade thus generating the majority of the force. As the blade goes from 6 to 9, it is trying to and does throw the water above it into the air where there is a lot less resistance, hence the rooster tail and less force generated. This is only my theory and I am not trying to argue with anyone, just throwing out my ideas and add to the discussion. I wish I knew more about propellers but most of what I have read applies more to completely submerged props.
kk

[phillnjack]

Now youve raced boats for 40 years and have the fastest boats that always win every race entered due to
you building ,designing and making the props yourself.
well i dint know that you were such a world authority on the props.
If i had known you were a grand master of science and physics with far too many degree's and doctorates on
the subject of hydrodynamics to mention, then ofcourse i would have to bow to your superior knowledge on the subject.

I thought you were just a boat driver who raced boats for fun.
drag factor on water is and can be a very misleading thing ,many new boats have come along over many
years and are said to be so efficient etc.
We see computer aided technology and the best brains in the world, yet many people still revert back to
older simpler and it would seem better ideas to win races.
prop development has come along way, but also a lot of the latest designs have actualy come from hit and
miss idea's as well.

Now when it comes down to talking about mercury or any maker spending millions etc to get the perfect prop,
then why is it that independant people such as the owner of this site can often make a better prop or am i wrong again?

and if i ask a question and get a silly answer im just supposed to live with it yeah ?




phill

[byrdsperformance@tds.net]

It explain's quite a bit of info
Phill'
At one time quicksilver by mercury had a book. I think it was called ALL YOU NEED ABOUT A PROPPLER.
If you can find one of these it's a help.

[Danny Pigott]

Funny I see Bill Van's name in the APBA Record book but not yours Phil.

[88workcar]

No i would not believe someone trying to tell me that the water within range of a raceboats prop is heavier at the bottom than top.
Anyone thinking this would be realy thick and shouldnt be allowed near machinery.

Now just because someone has something that works perfectly and does what they wanted it to do when they first invented it,dont mean they know how it works scientifically.
That we only have to look at the wright brothers to see what i mean about that.
Although they got mans first flight in a aeroplane to work,it wasnt the way they thought it was that actually got the plane off the ground.


Now then comes the nice long theory by Bill van steenwyk
he wrote
"Now imagine it lowered on the transom so ALL of the blades on the prop are completely submerged in the water at one time. Which location of the prop (depth in the water) do you think will give you the best speed, all other factors remaining the same. "


well to answer this one would look at a torpeedo or submarine.
The only place where the prop is not as efficient is where its attached to the torpeedo or submarine.
If this is just attached through the hub and no skeg or fin to disturb waterflow then the prop is efficient 360 degrees
of its travel..


I can understand that surface props are made a certain way to cut into the water at surface, and probably a lot more going on than just that at that moment.
But once the blade is submerged its trying to pull itself through the water.

It would be exactly the same if it was trying to pull through a solid medium.

With surface i can see the prop is basically doing nothing for 50% of the time if the bullet is level with the water.
And i can see there is going to be a touch of water slippage at the point of the skeg.
But for the prop not to be pulling at the 6 to 9 oclock does not seem right and no reasonable explanation for this.
the water is no different between 6 to 9 than 3 to 6 other than it will have a drop of air with it carried in with it by the blade out the water.now that blade to me is obviosly not working as hard as the one thats lost its air !!!!!!!!!!!!.
so therefore the blade from the 6 to 9 would infact be the one pulling harder if anything !!!

For those that dont like answers being questioned then i suggest you get a life and dont just be sheep.
Yes i am argumentative, and thats my perogative , as i want to find out the true answers to things not just accept anything told by someone else who dont realy know the answer.

without questing things we would never get any improvements in anything at all let alone props.
the Prop shop shop experts are allways comming up with new improved props to give better performance.
so they too must be questioning the effects of blades in the water and how they are realy working.

I thought the whole idea of a forum was to get answers and have debates to find out a lot more on the practical and the theory of the workings of boats engines and propellers.
if this is not the case then i shall just sit and read and wont bother asking anything.


phill

I do agree with this Phil, But thoery does not always work and some things need no explanation, and regaurdless of theory and understanding sometimes experiance prevails. I will stay out from now on, good luck, keep us posted with progress.

[Glenno]

Hi phill,

I have been pondering on the good questions you have raised about surface props etc.

I will try to explain what I have found with surface piercing props through the years I have raced, I have been told I explain thing like crap by my apprentices over the years so bear with me.

1) You need to think of the water not at rest but at speed, yes its the same water but it responds differently at speed.
example: If you fall off a water ski at 25 mph you sink below the surface very fast, even the initial hit leaves a big hole in the water but if you fall off a water ski at 70mph the water is like concrete and you barley scratch the surface till you slow down.

2) Its very true what you are saying about props blades being fully submerged get better thrust (I can't aggree more) but also at speed- having that much gearcase and prop blades in the water is not eficient for creating better speed because of the drag factor. At a decent speed if you are getting enough thrust with only 2/3 or 1/2 the prop blades in the water why would you bury the motor deeper creating more drag, losing rpm and making the motors job harder, then you would have to lower the pitch of the prop blades as there would be more drag (more potential thrust yes very true but you only need so much for a light race boat) you would end up back with the standard factory set up as that is best for thust and every day boating. I have found with a surface piercing prop set up corectly you can run around 40 to 50% bigger pitch and sometimes smaller diamiter works better (on a light boat set up well) than a the factory props that come on the outboard while hitting better rpm than the factory props. I have also found once you get the surface props up to speed they grip very well and on one of my boats I am only getting 2.1% slippage.

3) A snow mobile can drive on water at speed, so can a motor bike car- look on you tube, good examples of water at speed!

I hope this helps,
Glenno

[Fast Fred]

30 feet of depth = one atmosphere of presure, 60 feet deep = two atmospheres, and so on. this is 3rd grade stuff 45 years ago. every bodys a tuff guy sittin at some key board hidin at there desk usein a fake name. i am Fast Fred, hear and ware i'm standin.

[Tim Kurcz]

How about water pickup at the bottom of the skeg? This allows positioning of the gearcase bullet at/above the water, eliminating drag almost entirely without risking loss of cooling water. From that position, all prop theories can be safely tested.

Tim

[Aeroliner]

A pressure of 1 atm can also be stated as:
≡1.013 25 bar ≡ 101325 pascal (Pa) or 1013.25 hectopascal (hPa) ≡ 1013.25 millibars (mbar, also mb) ≡ 760 torr [B] ≈ 760.001 mm-Hg, 0 °C, subject to revision as more precise measurements of mercury’s density become available [B, C] ≈ 29.9213 in-Hg, 0 °C, subject to revision as more precise measurements of mercury’s density become available [C] ≈ 1.033 227 452 799 886 kgf/cm² ≈ 1.033 227 452 799 886 technical atmosphere ≈ 1033.227 452 799 886 cm–H2O, 4 °C [A] ≈ 406.782 461 732 2385 in–H2O, 4 °C [A] ≈ 14.695 948 775 5134 pounds-force per square inch (psi) [D] ≈ 2116.216 623 673 94 pounds-force per square foot (psf)

I beleive that 33.83 ft of fresh water is the corret number.

Alan

[BJuby]

Thanks Alan, I was going to state 30 feet (which I know in passing from my father who dives). I knew 6ft was not 2 atm. You gave the actual calculations, much better, haha.

[phillnjack]

Glenno
i understand exactly what your saying, and yes i understand that surface props can be larger picth due to only being half in etc at speed, that makes good sennse ofcourse.
And yes your right, when i do fall of ski's (very often ai do sink almost straight away.
what i cannot understand is the blade causing drag while its actualy turning and pulling through the water.
From my understanding of surface props and i have only run them on a small scale is that they are made to pierce the water far better than a submerged prop.

Im not being thick or trying to be smug, its just that this all seems to be going completely against
everything ive been told about propellers before.



phill

[Glenno]

Hi Phill,

I dont think your being thick or smug, I ran through all the same questions when I started racing, as the way race boats props run was also against everything I had learned over a life of being around outboards.

Quote: "what i cannot understand is the blade causing drag while its actualy turning and pulling through the water."

I think maybee another word to use would be load instead of drag - deeper gearcase definately drag but prop more load when deeper. So what I reckon is - if your getting enough thrust with only 1/2 prop in, if you were to lower prop into the water more it would load it up more (more potential thrust - bite, if the motor could spin it yes).

The whole idea of surfacing the prop is to unload the motor so it can rev more and spin a greater pitch prop.

On one of my boats with low pick ups the centre of the nose cone is around 5/8 above the water when the boat is at full go and the prop is only 7inch diamiter by 10inch pitch- I will try to upload footage to you tube as you can see full nose cone out and at least 1/2 prop out, still with great bite. When I bought that boat it was doing only 56mph and then I raised the motor 3/4 inch and it felt like it freed the motor and released its shakels and now it reaches 71mph.

If there was a motor that could have the power to turn that 7 x 10 prop fully submerged at the revs I am getting while srface piercing, i dare say it would hit the same top speed, if you ignored the extra gear case in the water drag. But you dont need that much bite, thrust, load on the lite tunnel hull its on. But if you where to put my motor (surface piercing) onto a regular every day fishing boat it would be totaly useles, not enough thrust to get it on the plane.

Any way I warned you I have been told I can't explain things, I will try just the same.
The Glenno

[phillnjack]

glenno, you explain things very well, i do understand what your saying about loading up etc.
it makes a lot more sense than saying drag to me, maybe different language thing, we might all
talk supposedly English but many things are very different.
It took me ages to find that wrist pin is what we call gudgeon pin, ha ha .

Now i know this might sound daft to some, but if the engine is pulling 6,000 rpm (i think its limited to this)
with a 13.25 x19 pitch fully submerged, what sort of pitch and diameter would i need if i go up to surface ?


phill

[Glenno]

Hi Phill,

Now we are talking!
What is make and HP is your outboard? And what sort of boat are you running it on?
6000 is good rpm for fully submerged, sounds like a good start!

After we all find out what HP and make your motor is and hull there will be some great input for you I am sure.

Standard motor examples I or friends have prop surface pierced,
1) 125hp mariner 4 cylinder ended up with a 24pitch 4 blade chopper
2) 150hp merc V6 - Low pick ups ended up with a 28pitch three blade cleaver.
3) 50hp Yam ended up with a 26pitch three blade chopper (very very very light mono hull)
4) 90hp Yam ended up with a 26pitch cleaver and same speed with a 24pitch chopper- different revs
5) 30hp tohatsu ended up with a 19pitch three blade chopper on light tunnel
6) 18hp tohatsu ended up with a 16pitch two blade chopper
and so so many more!

It does come down to trial and error a bit as believe it or not, one prop may work awesome on one boat and crap on another with the same motor.

but let us know make Hp and maybee even a pic of the boat from the side and a transom shot where I can see the under side hull shape.
Have a good one Glenno

[phillnjack]

My boat is not a race boat by any standards,its a bit too heavy as it weighs 500 pounds empty on its own.
The engine is a evinrude 56ci 60hp.with power trim so again is running heavy at around 260 pounds.
The shape when you look at the boat is very similar to boston whaler, but the underneath is very different.
The boat is like a cathedral when stationary ,it is deep v at the front but runs on the v and
2 sponsons untill around 30mph, then when more power is applied it runs on the just the back
3 feet and that is shallow v.
Recently i done some repair to the underneath and made the back pad a flatter about 1 foot wide.
this seems to have made an improvement in the handling of the boat and stop it from trying to
torque steer.
Here is a pic of when these boats were first tested out with a 2 cylinder 50hp back in the
early 1970's, youl see the boat running on about the last 4 feet of hull, this is what it runs at
around 35mph.
The more power you apply the less boat is in the water at the back end.
when i give full power with my 60hp and the nose kept at about the same level as in the pic, only
the last 2 foot of the boat is in the water.

When these boats have a 50hp on them and a average deep v 13ft speedboat is fitted with same
engines props etc, the orkney will out accelerate them but be around 2-3 mph slower top end.
Hope that makes sense.

Anyway here is the pic of the orkney 4 metre, its the original prototype and mine is the same.
Also a pic of one from the back and the underneath of mine during repairs.
the repairs were sanded and done propely in the end but this shows shape of underneath.
.52096
.52092
.52090
.52093
.52094

The deep v centre finnishes at around the point of engine control box, then tapers to shallow V

The transom is exactly 20 inch from top to bottom.
i run with engine equal to 3 holes up at the moment with cave plate about 1 inch above water on full throttle.

This is why i was thinking about low water pick up if i raise the engine bu say 4 inches etc.
like i say its not a race boat but i want to go a bit quicker.


phill..:cool:

[89HST]

You'd be surprised how high those cases will run..



http://i252.photobucket.com/albums/hh15/Transpiria/HPIM0965.jpg

[phillnjack]

Wow yeah that is high compared to mine.
And that runs fine with no extra water pick up ?

if the engine wasnt on a set back and jujst raised would you still go as high without extra water pick up ?
what i mean is, im gonna try and a get thing fabricated to raise my transom instead of having a setback,
Now by staying close to transom would the 4 -5 inch lift still get enough water ?
or is it just best to get the setback with the jack up all in one piece like the one pictured above ?

That engine looks very nice
can i ask what prop your running ?
and what sort of speed you get compared to it being at "normal" height
is the hole shot still not too bad ?

once again that engine looks very nice.


phill

[89HST]

24 raker, holeshot is terrible as these motors have very little low end torque, even with the vent holes in the prop opened way up. I made a plate than bolted to the set back that helped it a great deal for getting out of the hole. Once the motor hit 3k the party started like turning on a light switch. Stock it ran 65-68 mph @ 7000.

I had a 1500 xs on it for awhile but that was a little over the top. Boat and motor are painted to match now, fun rig.

[phillnjack]

you must have a different gear ratio to me. My engine has a 2.42 gear ratio i think !!!!
if my engine did 7,000 rpm with a 24 inch prop with zero slip it would only run 65.7mph
But mine im sure is limited to 6,000 revs, so that prop (if my engine could swing it)would
give 56.34 mph with zero slip !!!!!!

i realy dont have any low end torque problems with this engine, its like power all the way through.
But ofcourse ive not tried to swing a bigger prop than the 19 sst that ive got on there at the moment.

phill...........

[Glenno]

Hi Phill,

Now you will get lots of good input from lots of people I am sure!

remember also with props that if its stamped 24 it may be actually 22,23,24,25 or 26 by some one elses pitch mesure. measuring pitch is very hard. I have bought a 19 pitch in the past that was actually more like a 24 when tested on boat taking the speed revs and gear ratio calcs. I think some of the 75hp stinger motors had a 1.86 to 1 gear ratio but I may be wrong.

When you get that boat of yours set up and wound out you better hold on!!!

I aggree with you in that the motor should be no set back on that hull, It will make it safer and your hull looks like it may want to porpous if set up wrong, My feeling is surface pierce but not to much.

I would get the nose cone on, just use two part filler- forget the low pick ups. and if you can get your hands on some cleaver or chopper props to try in the 22 to 26 pitch range would be a good start. Remember you can always move the props that dont work on your hull out via ebay as I do (trial and error).

Any 60 70 or 75 hp guys please add your info for Phill
Glenno

[phillnjack]

we are so limited in the uk as to props and finding different types etc.
its only on ebay we find anything at all, not many race boat places and they dont seem to sell anything used.

i keep seeing a particular prop on ebay,i missed a good one a few weeks back, and it went for silly money,
the prop was a over hub 12.5 x23 omc stainless and made $80 us dollars.
i could of kicked myself for missing that one, but the michigan is still on there for about $110 buy now.
It says Michigan Part no. SS0523, but i cant find any info at all on the prop so might leave it alone,nobody
else seems to want it and it says brand new still in box but old stock.
when i see the props by ron hill they look so good,proper master pieces of artwork, and that raker on
your 75hp realy look the business.

i am going to try and see if i can get a transom lifter fabricated that only gives me about 2 - 3 inch setback to
try and keep it close.
I dont know what to think about a long setback as never used one at all.
Plus the longer the setback must put more strain on the transom,especially with a lift as well ????



phill

[89HST]

Your boat does'nt need a nose cone, your best max height is probably going to be 2-3 inches up and a 21 inch raker or renegade. The single cable steering and sitting on a plank is going to make it enough of a challange as it is.

[phillnjack]

The engine is only being operated with single cable for now to make sure the motor was going to be ok.
I should be picking up some hydraulic oil this week and then the hydraulic steering system is going on.
The steering ram end is a morse C3000-OB heavy duty and the matching helm to go with it.
I prefer to have hydraulic steering due to more precise steering, plus i like the idea of straight ahead if
i want to let go when going slow etc.
My hydraulic takes about 3 pints of oil to fill, so im buying a gallon of aeroshell 41 from an airport,its the
same stuff just a lot lot cheaper than the teleflext/seastar/baystar fluid just with a red dye for aero use.

I hope to get the hydraulic oil and give the system a test this week then if all is well i will cut the large
hole needed in the consol to take the helm unit.
The morse hydraulic system i have (so ive been told) is rated for upto 300hp.
I think this steering system should be ok for my boat, i hope it is anyway.

52156

52157

Obviously i will be re-spraying the helm unit and ram housing before they go on the boat to
keep the parts from getting attacked by fresh or salt water.


The engine sitting on a plank ???????
Oh no, if i get a jackplate fabricated it will be from stainless and will encompass the transom with
a welded hollow block on top, it will all be made of around 3/8th thick 316 stainless steel.....



phill..

[Jfarrelly]

Where did you get or how'd you make your nosecones/low water pickup

[Ron Hill]

How about water pickup at the bottom of the skeg? This allows positioning of the gearcase bullet at/above the water, eliminating drag almost entirely without risking loss of cooling water. From that position, all prop theories can be safely tested.

Tim

My dad made my brother a gearcase for his "A" Hydro in 1949 and my brother beat 32 "A" Hydros in the Hearst Regatta.

Because gearcases are in my DNA, I have wanted to make a stainless steel gearcase and part of that concept was to have the water pickup in the skeg.

A stainless steel gearcase could be made very thin and the skeg could be larger but thinner...

Maybe, in my next life Tim.

[zul8tr]

Lets pretend the prop has NO FUNCTION as far as propelling the boat thru the water, other than the fact it is there in it's normal location, on the prop shaft, and in the water. In this visualization, propulsion is being achieved in this example by ANY other means you might imagine EXCEPT the propeller. Could be water pump, sail, oars, or any other type power that will move the boat forward through the water EXCEPT that prop on the motor.

Now imagine it raised on the transom so only a part of one blade is in the water at any one time.

Now imagine it lowered on the transom so ALL of the blades on the prop are completely submerged in the water at one time.

Which location of the prop (depth in the water) do you think will give you the best speed, all other factors remaining the same.

Same thing applies when the prop is driven by an engine and that prop is the sole propulsion for the boat. The more blades in the water, the more DRAG. It also may be easier to imagine the prop as a complete disk. The bigger the disk the more drag. If the disk has holes or slots cut into it, drag will be reduced. That is also the reason a jet airplane is faster (among others) is an airplane with a propeller generates much more drag than one without. Add more propellers (think 4-6 engine bombers) and more drag. In addition, the tips of the propeller reach supersonic velocity while the vehicle itself is much below the speed of sound, also leading to propeller inefficiency. That and drag is why a prop jet is slower than a pure jet.

There is much more to it than just this, just as air is much different than water insofar as the way it acts when moving through it with a propeller or any other object,and that is where number of blades, pitch, diameter and other factors enter into the equation. BUT one of the large things to effect a prop (or any other object moving thru air or water) is DRAG. This is also the reason that some still run props with only two blades when racing, although not a lot anymore. If water conditions will permit, a two blade will probably be faster (taking into a lot of other factors) than a multi blade prop, especially when you are running a surfacing type prop, is there is LESS DRAG with 2 blades than 3 or more. This is not always true, depending on handling problems you might encounter in rough water, etc. You can raise a multi blade prop higher out of the water and have the boat have better handling capabilities because of that word again, DRAG. Eventually you get to a point where handling and prop efficiency become more important than drag reduction, especially if you can not control the boat anymore because of lack of directional control which the lower unit/prop combination in the water give you.

Unfortunately there is no magic formula which will allow you to calculate this point. The only formula is testing and good record keeping.

Hope this helps.

Although this thread is a bit stale I figured add'l info wouldn't hurt.

Bill is right about the theory he presents above for the working part of the prop in the water with low air mix doing the thrust work.
Back in my racing/experiment days with 1:1 gears on a Quicki H tower using 2 cylindere Merc with a 2 blade prop I was searching for more speed. To get it I would syncro the prop to the piston position by trying different spline positions of the drive shaft to the crank. What worked the best for more rpm and speed (about 1 mph which is a lot in a race) was to get the prop blade to dive at about the 9 o'clock position (looking forward) with the piston at TDC (not many choices with the limited spline numbers but it can be done). Never played with this using 16:21 gears and 2 blade props & 2 cylinder engines, figured it wouldn't help due to the cyclical nature of blade feed to TDC position. Also indexed the plugs.

[ice_spy]

Again, thread may be a bit old but I'd like to give my stance on the 100 view car crash.
From my understanding on propellers, it is like a screw. The pitch varies the amount of travel, the gear ratio and amount of prop slip (no or less drive) also factor the amount of travel forward in one rotation. Drag is a big factor here, ive never seen an efficient submerged race prop on a race boat for a reason. The other term mentioned is piercing. Surface prop or surface piercing is definitely two names used. When it comes to submerged boat props, most designs are very similar with the exception to allow some cavitation with less slip. This design comes into greater play when two most common surface props are used. Chopper and cleaver design. Each design although both surface type props offer different results. Choppers are known for bow lift and cleavers for stern lift.
As said, i also believe that 1 blade is most efficient in drag as obviously none would be best for drag. You cant run 1 blade for ballance reasons therefore 2 is the next best. Im not goin into conditions and hook up other than obviously race props with more blades like 5 on F1 tunnel is too hook up better and smoother, but like when going from a 3 blade to 4 on a fishing boat, it lowers rpm.
So to go faster, you need more pitch, to run more pitch you need less drag, to have less drag means you have to higher. Too high the amount of drive is lost. The prop design is tested and made to run at this happy medium. No submerged prop has been invented to run at the same effectiveness as surface drive with the same amount of power/ boat set up etc.

[John Schubert T*A*R*T]

Although this thread is a bit stale I figured add'l info wouldn't hurt.

Bill is right about the theory he presents above for the working part of the prop in the water with low air mix doing the thrust work.
Back in my racing/experiment days with 1:1 gears on a Quicki H tower using 2 cylindere Merc with a 2 blade prop I was searching for more speed. To get it I would syncro the prop to the piston position by trying different spline positions of the drive shaft to the crank. What worked the best for more rpm and speed (about 1 mph which is a lot in a race) was to get the prop blade to dive at about the 9 o'clock position (looking forward) with the piston at TDC (not many choices with the limited spline numbers but it can be done). Never played with this using 16:21 gears and 2 blade props & 2 cylinder engines, figured it wouldn't help due to the cyclical nature of blade feed to TDC position. Also indexed the plugs.
My father always did that with my brother & my motors. Not sure it worked but one would think that at the #1 cylinder firing position with the prop just clear of the gear case you would theoretically get a better bite

[Tim Kurcz]

My father always did that with my brother & my motors. Not sure it worked but one would think that at the #1 cylinder firing position with the prop just clear of the gear case you would theoretically get a better bite

61022

[fs5]

Wow dose that pump enough water to keep the motor cool.
Great idea mate!