Sorensen long haul center fin

[Jippe]

Plans call 9"×3" center fin but theres nothing about that where it should be, I need advice for that.
If I dont find just that size fin, is it better to use little smaller or bigger?

[champ20B]

Plans call 9"×3" center fin but theres nothing about that where it should be, I need advice for that.
If I dont find just that size fin, is it better to use little smaller or bigger?

Jippe, you can buy extruded "T" aluminum by the foot online or at a nearby metal supplier. You can make your own fin this way easily.
Afterward, you need to polish it and sharpen it from the leading edge along the bottom edge to just where the trailing edge starts. Make sure it is perfectly aligned with the keel (perfectly, as not even 1/32" off).
Now......heres how to place your fin to start for testing. Being that your boat is a center fin traditional roll-up, the way is to locate the point of balance. You must put the motor on the boat, rig it up with all hardware, fill up the gas tank 3/4 full, and get in it with a pipe or mop handle across under the hull like a sea-saw. (It would be good to have it up on a platform or table so the motor can hang down.) What you want to do is to locate the pivot point (pipe or mop handle) forward or aft until the bow and transom are balanced level like having equal weights on a sea-saw. Again, this is with your weight in the boat fully rigged. That would be the approximate ideal spot for your fin. It is a good idea to be where you can move your body forward of the fin location in your boat in case you need to when turning to plant the nose a bit. But that depends on how it handles with your body weight.

You might find that the fin would be about 1/5 to 1/4 the boats length from the trailing end of fin to the trailing end of transom bottom. However it could be a little more still. Many guys on here don't like to share much of this kind of info or just don't really know, as I found out when I asked about fins once. I hope this info will help.
Just be careful not to damage the hull. You might want to make a narrow flat padded board (2 X 4) with a mop handle nailed down along lengthways of its center. Put the hull on the flat board with handle underneath.

[Jippe]

This is good info, thanks. Is it center or maybe offset left?
I have boat almost ready and it is still in my garage on the table.
Painting, varnishing and rigging is not done yet.

[champ20B]

This is good info, thanks. Is it center or maybe offset left?
I have boat almost ready and it is still in my garage on the table.
Painting, varnishing and rigging is not done yet.

Jippe, if you want to get right and left turning capability, it will go center.....however, in the past they would mount the fin left a bit. It would be between the next stringer and center keel I think. Glen-L boat gear also sells fins. They have a high speed shark dorsal style fin that might work well on your C-class runabout. It is a cast unit that may require milling on its mount plate to make sure its 90 degrees. It would need to be polished and sharpened to your liking as well. You can make a regulation type (long rectangular w/rounded corners) using 1/4" thick "T" extruded aluminum as well. Don't worry though about drag. Fins really don't have enough drag to amount to anything as long as it is in line and true. A fin that stays in contact with water though, at speed, is a good fin in my opinion.

[champ20B]

Jippe, I forgot to tell you also, that mounting left is mostly for left turn "closed course racing". It reduces right turn stability....

[Krazy Karl]

On my Long Haul which I didn't build has 2.5" x 7" rounded fin positioned 29.5" from the rear of the planing surface. It is 9.75" from the edge of the left side planing edge and 20" from the right side. This boat is the second Long Haul generation with the 2 angle non-trip chines, a vast improvement over the first version. It is a lot better handling boat than the first which I started with. I would NOT center the fin on one of these boats as they will turn hard to the right when they hook. The counter-rotating prop will add to right hand turns significantly enough to throw you out if you are not expecting it. A
"D" Merc on one these will throw you out on a regular basis if you are not careful.
These are fabulous Marathon boats and handle rough water like a dream. I have run Top 'O twice with my 1st generation with a Yamato and want to go again with my second. By the way Darrell is a good friend who designed these boats based on a Hill boat if I remember correctly.
kk

[champ20B]

DAM, IM GOOD!!! 29.5" forward? That is just what I estimated!!! I said it would be about 1/5 or so the length of the boat forward from the transom!!

But I would place it balanced with the motor and fuel tank location etc your running Jippe. Just find the balance like I recommended to get it right for your particular set up and weight, to get it just right, as far as linear placement goes. Adjustments can be made afterward from testing if necessary (forward/back-center/left).

I really didn't know that such a great (left/right turning) marathon boat would need a left fin. That's a real surprise!!! I saw pictures of these guys in freeze frame after jumping a wave with similar boats, and I swear I saw those fins right in the center of the exposed planning surface. I don't see roll up "C" class though in closed coarse racing, so I never seen a modern "C" boat with a left mounted bottom fin. They were around a long time ago and I seen old pictures of them. All I ever see are side fins now days.

[Jippe]

Point of balance is 29,8 inch from rear :)

Next question is yamato 302 trim angle. With stock adjustment system I cant get it even paraller.. It is negative with max. setting.
What is good angle to start with? Paraller to bottom?

[zul8tr]

Start parallel and pick a height like 1" below bottom for rear center of the prop shaft. Get speed and rpm and note the attitude of the boat: is the bow up or low to the water? If low kick it out a bit, if high kick it in a bit. Note speed and rpm and ride characteristics each setting. Then try higher with level shaft and repeat above. Note water conditions will change things for all settings as well as different props, many combinations so have safe fun.

You also need to decide what your goal is for the boat: top speed, good turning, etc, a compromise will be needed to achieve several outcomes.

[Jippe]

First test drive done. Shaft is paraller and 35mm below.
Boat porpoising very much (bow up and down). When moving my weight to forward it helps little bit but not much.
What causes this? Prop, trim angle, motor height?

Water was dead flat and prop 3 blade dewald cleaver.

[Tim Weber]

You are not maintaining the plane. Either you have a rocker in the bottom or the plane is too short.

The bottom needs to be dead flat for 36" or so before it breaks. If you have a rocker " bump " the boat will react to it. If the plane is to short that can cause it to oscilate.

Tim

[Yellowjacket]

Tim is of course correct, if the bottom isn't flat it will porpoise. In addition you have the engine mounted too low, if the shaft centerline is 35mm below the bottom, it's almost twice as deep as it should be. First thing to do is check the bottom and raise the motor up at least 12mm. You may also want to add some tuck into the setup (which will also drop the motor down more so you will need to raise it up some more after you do that.

[Jippe]

Last 30" is dead flat, then it start to break "v", just like plans show. I found hydroracer.net thread where they mention 1/8-1/4 tuck. I assume that means negative trim but how it is measured? 1/8 from where?

[zul8tr]

A trim tool is usually used that attaches to the prop shaft that has a long straight piece that goes under the bottom. The trim is measured from that straight piece that is parallel to the prop shaft center line. You would measure up from that to the bottom at 2 points separated about a foot apart, the difference in the measurements is the amount of tuck or kickout. Here is a pic of such a tool, it is the one on the left. The other measures the depth of the rear end of the prop shaft center below the bottom.

http://hydroracer.net/forums/filedata/fetch?id=345350

They are very accurate if made right with a good snug fit on the prop shaft and the long piece truly parallel to the prop centerline with the machining. The tool needs to be checked for truly parallel of the long piece to the centerline of the prop shaft. A little bit of slop in the fit on the prop haft and off a bit on not parallel construction will greatly magnify away from the support at the prop shaft especially with the measurement taking farthest from the prop shaft attachment when dealing with 1/16 and 1/8 inch differences that mean a lot on these race boats.

There are other ways to measure the trim if you do not have the tool.

[champ20B]

First test drive done. Shaft is paraller and 35mm below.
Boat porpoising very much (bow up and down). When moving my weight to forward it helps little bit but not much.
What causes this? Prop, trim angle, motor height?

Water was dead flat and prop 3 blade dewald cleaver.

Jippe, hopping is not uncommon with kneeler runabouts at all, as long as it smooths out once you push the throttle open. You might need to go to about 3/4" shaft depth (center shaft end, to surface) once everthing is worked out. I think that's what the rules allow on "C" class Yamato powered runabouts "if I'm not mistaken"....It would be a good idea to double check the stock outboard tech manual on the APBA website about this stuff to get it right. It is important set up info that could help. It is on the sight and you just click and load it to read.

My "B" mod runabout does the same thing until I open it on up...then it shoots on past 65+mph on real quick. I'm running a nice built Yamato 80 with a custom gearfoot of my design. I have mine at 1/2" below with a 2-blade cupped and edged prop that I had done. I'm running neutral (level) lately. I started out deeper and realized that I could get an extra couple or more MPH raising it on up. I followed ZUL8TR's advice on this and a few other tech info a while back, and it helped me out.

When I start off, it cavitates. I just hold it at about 4000 or so RPM, then after a short bit, the RPM drops as the prop grabs and it accelerates hard. The ride involves a bit of galloping until I squeeze the throttle to smooth out and huddle myself down back and low. The ride is so fast, its hard to remember it.

[Jippe]

Thank you all. I try 3/4 shaft depth next.
Do you use some non-stock thrust brackets on yamatos?
I dont have that trim tool.

[Jippe]

20mm below and little bit negative trim. It porpoise less than yesterday but still too much..

4 min. video
http://youtu.be/pGfsdnRPbGI

[champ20B]

20mm below and little bit negative trim. It porpoise less than yesterday but still too much..

4 min. video
http://youtu.be/pGfsdnRPbGI

It looks like its running pretty good to start!....There is another video on tube that has a fellow "Charlie Smith" testing a DSR racer and it hops a bit more than your doing as is now. If you were racing other boats at the time, the water would be a bit more rough, and your hull would be running perfect in that kind of water. As far as tuck, what that means is 1/4" or 1/8" difference in height from the center end of shaft to the center nose of the gear case (where the other shaft end would be). This is in relation to the level keel line. As far as the bottom design, yours is correct. What those rules mean is that the keel has to be level for at least 36" forward till it starts the rake up toward the bow. It could be more if one wants, but no less. The planing surface has to be flat at least 18" forward from transom. It could be more, but not really necessary. When your boat is running at racing speed, it should only be running on around the last foot of pane surface anyway if its doing good. You followed the plans and your hull is just right.

[Yellowjacket]

Looks like you are getting it dialed in. A bit more tuck and you should be fine. You need to also make sure you are running fast enough, the faster you go the more it will smooth out. What prop pitch are you running, how fast and at what RPM's are you turning it? Also, you said you had a clever on it. What rake do you have as this makes a big difference. Most older runabouts didn't use cleavers, they tended to use round ear props, but I don't know what the current thinking is on that. The amount of bow lift that the prop contributes can make big changes so that could be your issue. I think if you get it running fast enough you should be fine but if this prop has too much bow lift it could be the biggest cause of the porpoising. I would talk to the Sorenson folks and see what prop the recommend.

[Jippe]

Yes, almost there :) I just tried two, two blade prop and porpoising was totally gone around 40-50 mph.
I think those should be run deeper than 3/4, because engine was screaming and there was huge water spray behind.
I have one more prop to test, 3 blade ron hill cleaver 6 1/2 @ 11"

First prop was 3 blade dewald cleaver, marked "osy 400 qualifier", I dont pitch or rake..

[Jippe]

Few pictures

[zul8tr]

Your pics do not open, a message comes up that they are invalid.
Tell us what pitch, rpm and speed these props are giving.

[Jippe]

Tiny tach wont work anymore, its stuck to 1850.. so I dont know rpm.
First 2 blade: 6 5/8, 12-14 1/2, second 6 1/2 12-13 5/8, both cupped thats why pitch range.
Speed was only 50-55 mph max. They were slipping and spraying water too much..

With dewald max speed was 58 mph, rpm 5800. I didnt dare to drive faster because it was porpoising so much

[champ20B]

Tiny tach wont work anymore, its stuck to 1850.. so I dont know rpm.
First 2 blade: 6 5/8, 12-14 1/2, second 6 1/2 12-13 5/8, both cupped thats why pitch range.
Speed was only 50-55 mph max. They were slipping and spraying water too much..

With dewald max speed was 58 mph, rpm 5800. I didnt dare to drive faster because it was porpoising so much

You mentioned that you were going to test a Hill cleaver 11" pitch... I have seen the Ron Hill cleavers for Yamato engines. I honestly thought that they look a bit heavy for their size, but that's just me. The kind I'm referring to are the "three blade" with the large solid hub, if that is what you have...

I sure would like to know how it stacks up though against the Dewald if the pitch is about the same. Those Dewalds are nice looking well designed props! I cant wait to read if the Hill cleaver really does the trick!

[zul8tr]

Have you pressed the reset button on the Tiny tach? I have had a freeze on my Tiny tach and a reset fixed it. When they freeze up I suspect the tach is not receiving a clean signal. I have this issue with my point style Y80 but not the 25ss with CD ignition. Maybe the battery is dead in your tiny tach, if it resets the battery is ok? Sometimes you have to press and hold the reset button for 5 to 10 seconds before it will start the reset process.

Is your Tiny tach the old model (1C or 2C) or the new type that allows adjustment for different engine types?

How do you know rpm with the dewald prop if the tach is not working?

What type of device are you using for the engine kick in or out?

[Jippe]

Tiny tach is new commercial model. It freezed yesterday. I didnt know that reset button has to be press that long, i'll try again, thanks!
Engine kick in is measured with level against bottom and meter to anti cavitation plate. Measurement points 27cm apart.
If you ment engine adjustment system, it is original.

Edit: Tiny tach new model has only select button visible but I found reset button under the front face sticker. There was also something like silicone, I dig it out and found reset button. Now it works again.

[Jippe]

Ron hill cleaver 22mm below, 6mm tuck -> 49 mph @ 8200-8400 rpm
It was very hard to get plane.. no porpoising and turns well.

WTB: proper prop :rolleyes:

[Jippe]

Dewald prop back, 22mm below, 6mm tuck. There was little weather change, winds now 2-3 m/s. Now it works well, no porpoising but speed was only 54 mph @ around 8000 rpm. On wetback this prop 63-64 mph @ 6200 rpm.
Actually rpms was 7000-9000, so I assume there was too much slip on prop.

There is one four blade 7 @ 12" round ear prop on ebay, I'm thinking buying it. Would it work?

[zul8tr]

Ron hill cleaver 22mm below, 6mm tuck -> 49 mph @ 8200-8400 rpm
It was very hard to get plane.. no porpoising and turns well.

WTB: proper prop :rolleyes:

Way to may revs, get more pitch on that prop. When you reset the tack did you by chance upset the setting for the engine type and # of sparks per rev?

[Jippe]

Yes, settings are set to correct. I heard it from engine sounds that its slips and revs go up.. also lower speed reading is what it should be.

[zul8tr]

B4 you that 4 blade a prop (I wouldn't for your application) test more with the ones you have. Since they are a far amount less than 7" diameter and your revs are way up there (with excessive slip from your descriptions) I would try deeper (drop 1/2" same tuck at first) and see if that holds better and the revs tame down. You should look for about a steady 7100 rpm and with a 12" pitch that should get you near mid 60's for the 302. A 7 x 12-4 blade might work but probably will be slower than a 3 or 2 blade but it will definitely drop the revs.

[Jippe]

Dewald actually is 7". Few pics, dewald on right.

[champ20B]

Ron hill cleaver 22mm below, 6mm tuck -> 49 mph @ 8200-8400 rpm
It was very hard to get plane.. no porpoising and turns well.

WTB: proper prop :rolleyes:

A pitch of 11"-12" is about what you should have. If this Yamato is running a 1:1 gear ratio or close, then with 11" pitch @ 8200RPM the theoretical speed should be at around 85 mph. With about 90% efficiency it would be about around 75 mph which is unrealistic for a "C" stock runabout anyway.........something is wrong somewhere. You was only at about 40-50% efficiency range. That is not good at all.

The real range you need is 6500-6800 rpm and about 60-63 mph top end. That is what this type of boat should actually run at top end and be good. That is with 11"-12" pitch prop.

If your gearfoot has any modifications to the shape, ect..... then that may be something to examine.

[Jippe]

I have done lot of testing.. I found that best setup is shaft paraller and 18mm below. Now I can control it by moving my weight.
Top speed is only 51-52 mph @ 6400-6500 rpm, dewald prop.
Same engine, same prop on my wetback, speed was 63-64 @ 6200 rpm.
Where is missing speed? :confused:

[John Schubert T*A*R*T]

I have done lot of testing.. I found that best setup is shaft paraller and 18mm below. Now I can control it by moving my weight.
Top speed is only 51-52 mph @ 6400-6500 rpm, dewald prop.
Same engine, same prop on my wetback, speed was 63-64 @ 6200 rpm.
Where is missing speed? :confused:
That's about the maximum speed that you should expect.

[Yellowjacket]

I have done lot of testing.. I found that best setup is shaft paraller and 18mm below. Now I can control it by moving my weight.
Top speed is only 51-52 mph @ 6400-6500 rpm, dewald prop.
Same engine, same prop on my wetback, speed was 63-64 @ 6200 rpm.
Where is missing speed? :confused:

First of all, I'm pretty sure the "Long Haul" is heavier than the "Wetback", and it is a runabout which isn't going to be as fast as a hydro. A hydro basically flies on a cushion of air and your Long Haul doesn't have that advantage.

That said, it shouldn't be 20% slower, but you aren't going to be able to use the same prop on the heavier, higher drag boat. The reason is that by putting the motor and prop on a runabout, you are taking the prop out of it's "sweet spot". For every prop there's a speed and rpm range that provides the best efficiency and best performance. With a heavier boat that has higher drag your boat speed is slower, so now your pitch isn't matched to the slip and boat speed and your prop efficiency is going into the toilet. In all probability you will need a prop with about 10% lower pitch, and you also might need slightly more diameter to reduce the slip. In addition, your Wetback gets a lot of lift from the cushion of air under the boat, and that reduces the drag, but also requires a different prop than the runabout.

Right now you are off of the prop efficiency curve and if you could get more speed out the boat it would go even faster with that prop, because it is slipping a lot and not working efficiently. At the same time you have a prop that isn't really designed for this hull and you can't expect it to work properly. Your current prop has a lot of "bow lift"(as evidenced by the porpoising problem), which means that it's actually digging in the planing surface and causing more drag that a prop that would actually lift the boat.

First of all, I'd put a fairing on the boat to minimize the aerodynamic drag, that's starting to be a factor at these speeds. Secondly I'd make sure the planing surface is prepped with a surface that is matte sanded front to back. If you can get a bit more speed I'd jack up the motor more since that is a big factor in drag.

After that you need to start looking for a prop that is better matched to your boat and is designed for a runabout as opposed to a hydro.

[Jippe]

New prop ron hill cleaver 7x12, shaft 35mm below and paraller. No porpoising at all, 55 mph @ 6000-6100 rpm. Best prop so far..
What kind of type prop works best?

[Yellowjacket]

At 35 mm prop shaft depth, you are still pretty deep. I'd expect that you would pick up speed by raising the prop, but at some point it will start to slip more and that will be a retrograde step. Deeper is worse in that the drag from the gearfoot is increased, so you want to run as shallow as possible. Typically runabouts used a three blade round ear prop, but that was long ago and some folks are having good luck with cleavers. More important is the rake, and diameter. Too much rake will result in too much bow lift and that will cause the porpoising. Not enough diameter and you won't be able to run the prop as shallow and will have more gearfoot drag. The faster you go the less diameter you need. Most runabouts like a little tuck, you might try that too, it may allow you to raise up the motor some.

Props are a very difficult and expensive thing to tune on a boat and that's why you need to tap into the experience base (Ron Hill or the Dewald folks) to have them get you something that is close in the start.

All that said, you are getting closer with each iteration. With the right prop and a higher motor setting, you should be able to get closer to 60 mph but that's probably as much as you can expect from this kind of rig. Also you might talk to the Sorenson folks and see how fast others are running on that boat, they should know that, and they should be able to give you a recommendation on a prop.

This is a difficult process and the learning curve you are on is steep. Since you aren't at local races and don't have the benefit of being able to talk to folks, try lots of props, and get help from experienced folks it's that much harder. You just have to remember the basics and keep at it, and the more you work the faster you will get.

Keep it up, you're on the right track.

[Jippe]

It start to slip at 30mm shaft depth, I got more rpm's but speed was 50-51 mph.
35mm and 2-3mm tuck, 55 mph @ 5900 rpm. 45+ mph no porpoising and it is very fun to drive, it's going like train.
Compared to wetback, I can turn and can go to rough water.
I have burned 200l gas so far :p

[Jippe]

I put dewald prop back and 37mm below, 3mm tuck. 58 mph @ 6300-6400 rpm
It goes faster when prop is deeper.. :eek:

[Jippe]

Same prop, same settings and lot of driving today. Here was windy and quite rough water today. I noticed on rough water that so called prop walk thing, not much just like little warnings.. Boat turn suddenly little bit and rpms rise quickly. I dont know right term in english but I hope you know what I mean. (Skeg rise out of water)
Is that normal behaviour in rough water?

[blackrook]

Dear Sir, I wounder if you have any photos of the Long haul on the building jig that you built . I bought the plans of the Long Haul from Sorensen Woodcraft. I like to get a look at your building jig you built your Long Haul on just reference thanks.

[Jippe]

Here is some building pics (http://www.moottorivene.info/keskustelu/projektit/sorensen-woodcraft-%27long-haul%27-projekti-t8260/0/)

[Yellowjacket]

Man that thing is built like a tank!!!!

With glass on the bottom like that you could have easily reduced the thickness of the bottom sheet by 1/8 of an inch at least.

Curious as to how much it weighs?

With as heavy as that boat probably is, you've done a pretty darn good job in getting it to go as fast as you are right now.

[Jippe]

It weights about 55-60 kg without engine and tank.
Bottom is 9mm okoume (back), front bottom and chines 6mm okoume.

[blackrook]

Thank you very much for your photos of the your building jig of Long Haul they help me very much to understand how to build the jig you are very kind person to help me thanks.

[Jippe]

Back in business with long haul. Still porpoising when I can't get it to speed enough. This setup needs just right weather or it not get enough speed. So, if I get more power, then it maybe goes well anf not porpoising. I bought new chinese pwk 32 carb and made adapter for it to yamato 302. Not tested it yet because my cable wire is hard one wire type and wont fit to new carb. Now I'm wondering is there any gain expected with bigger carb only?

[Jippe]

Is there way to measure prop rake? What kind if props you are using with runabouts?

[zul8tr]

On that prop it has positive rake because it tilts to the rear. Positive rake angle is the rearward tilt off the vertical from the prop shaft hub measured from the blade tip to the hub. To get the degrees of rake you would need to use an angle reading tool. Ron Hill should add his methods to measure. I think that bigger carb will not do much but worth a try. You will need to adjust the fuel mix for the bigger carb.

http://bblades.com/props-101/

example of visual measure of rake

https://www.bing.com/videos/search?q=how+to+measure+prop+rake&view=detail&mid=D34ADBF295F4162CE61ED34ADBF295F4162CE61E&FORM=VIRE

[Fastjeff57]

http://bblades.com/props-101/

Best explanation of Rake I've read to date.

Jeff