Need help from Ron Hill!!

[omcstratos]

Ive been testing my 11.25 x 18 Yamaha style cleaver and have had a little difficulty. I don't know how low is too low for this style prop to run but I am having a pretty rough time getting the prop to grab the water. First off, Looking at some of these pictures, I am worried that I am getting some exhaust to come around the thru hub and ventilating in the blades. My past experience with thru hub surfacing props are that they don't slip until the boat is about to break over and plane off. This one seems to slip immediately like an over the hub prop when throttle is added.

Secondly, this may be due to me not spending quite enough time playing around with setup but I don't feel like I have gotten 100% hook up from the prop when on plane. I can be cruising along for a while and back off the throttle and the prop finally bites in. I'll ease back on the throttle and immediately lose bite, and do this back and forth all day.

I've tried this with the prop completely submerged and the cav plate 2.5 in out of the water. I get slip and can't plane off at all with the prop submerged and with it raised it only improves a little.

I know cleavers like running high, but I thought it was odd that I couldn't plane off at all with the prop submerged. Any help???

[Ron Hill]

Sounds like too small of a prop in both pitch and diameter.

What is the horsepower of your motor?

This prop usually planes easy!

[omcstratos]

50hp OMC. I know I thought this prop wouldn't have much problems planneing!

[Ron Hill]

See if you can figure out the gear ratio. Some of those Nitro gearcases can swing 12 1/4 X 20-24.....

This is the 12 1/4 diameter....

[omcstratos]

After running it today my best numbers was 18pitch prop turning at 6200rpm and I only could get 34mph out of it. I don't know what the ratio is but its the small gearcase for the 2cyls

[omcstratos]

apparently the gear ratio for this motor is 2.42

[Ron Hill]

Keep the hub kit, I'll send you a 12 1/4 by 22.

[omcstratos]

Ok. Hmm I'm curious about going up 4 inches in pitch. How many rpm's does that normally drop? You certainly know more than me so I won't doubt your advice!! I'm still learning about surfacing props haha.

[Ron Hill]

Clearly the 11.25 X 18 is too small. When a prop just slips, no way of telling how much an inch or two will effect the RPM's. General rule of thumb is 2" of pitch is 400 RPM's...

[LittleCharger]

Where is the center of the prop shaft relative to the bottom/pad of the boat?

What kinda boat and how much does it weigh?

[Nason]

After running it today my best numbers was 18pitch prop turning at 6200rpm and I only could get 34mph out of it. I don't know what the ratio is but its the small gearcase for the 2cyls

I got the same prop,except it was tried on a 40 Mercury,42 mph was the fastest it would go. Slapped on a 3 blade power tec 10-3/8 x 15p fishing prop 45.2, slapped on a 10-3/8 x 18p mercury chopper 49.3

[zul8tr]

After running it today my best numbers was 18pitch prop turning at 6200rpm and I only could get 34mph out of it. I don't know what the ratio is but its the small gearcase for the 2cyls

For the 18" pitch, 6200 rpm, 2.42 gear ratio, and 34 mph that is about 22% slip which is very excessive especially if a light rig, this indicates probably more pitch needed for your rig. Do you know the total weight of the rig running?

With the 22" Ron is sending if you keep the same rpm(?) and slip in the 8% range the expected speed is about 49 mph.

Although not the last word like testing is I find this reasonable for estimates:

http://continuouswave.com/cgi-bin/propcalc.pl

[Ron Hill]

For the 18" pitch, 6200 rpm, 2.42 gear ratio, and 34 mph that is about 22% slip which is very excessive especially if a light rig, this indicates probably more pitch needed for your rig. Do you know the total weight of the rig running?

With the 22" Ron is sending if you keep the same rpm(?) and slip in the 8% range the expected speed is about 49 mph.

Although not the last word like testing is I find this reasonable for estimates:

http://continuouswave.com/cgi-bin/propcalc.pl

That prop chart is excellent, I just forget about it most of the time.

zul8tr, what peed to you think this boat should go? I can't quite see it. I know you've run a bunch of these boats.

Is this a 2 cylinder 50 or is this the three cylinder? I just don't recall this gearcases water pick ups.

[omcstratos]

Where is the center of the prop shaft relative to the bottom/pad of the boat?

What kinda boat and how much does it weigh?

I have tried everything from the prop submerged (and get slip) to running as high as water pressure will allow (not much better performance). It seems like it runs a little better up high even to plane off. Boat is a 16ft modified vee bottom even though looking at the back it looks more like a flat bottom to me. Its kind of heavy being 350lbs.


That prop chart is excellent, I just forget about it most of the time.

zul8tr, what peed to you think this boat should go? I can't quite see it. I know you've run a bunch of these boats.

Is this a 2 cylinder 50 or is this the three cylinder? I just don't recall this gearcases water pick ups.

Mine is a 2 cylinder 50 and the last of the OMC's made had the plastic water pickups before they became BRP. I wish it was a 3cyl,, I like the sound of them better haha!!

[zul8tr]

That prop chart is excellent, I just forget about it most of the time.

zul8tr, what peed to you think this boat should go? I can't quite see it. I know you've run a bunch of these boats.

Is this a 2 cylinder 50 or is this the three cylinder? I just don't recall this gearcases water pick ups.

Ron

Thanks Ron I always try to post helpfull stuff. It is somewhat hard to say what speed the boat should go because I do not have real good info on his boat. I would like to see the bottom, if there is a pad, a hook or rocker, the total weight when running, etc. But since I can't tell what his rpm's will be with say the 22" prop (you are sending) compared to his posted 6200 rpm with the 18" pitch all that can be done is estimate with the formula I posted, so my present estimate is near 50mph with the 22" if the 6200 can be sustained with low slip (8%). I have used the calculation with a lot of the boats I have run and in the light hydros I get very near the predicted speed with about 4% slip. I usually calc slip for a setup with the formula by running a measured distance and timing the distance covered that gives avg speed then use the formula to get slip. Then slip can be used in other calcs with that prop and rpm. The heavier the hull and depending on the bottom design the more slip that will occur for a planing hull. Props have always been an experiment to get them right. I suspect he will have to lift that 22" pitch baby way up to get the revs. Hope his water pickup is low enough? From tje pics posted of the lower unit I suspect it can be raised at least as high as so the bottom is level with the low horizontal crease on the water pickup slot because water will rise up the case from the bullet nose and get in the slot. Note that when hull weight increases the operation of fully airated props (surface piercing) on vee bottom hulls becomes more difficult to achieve with low slip and to keep the revs up with bite.

Pete

[omcstratos]

Here's some pics of the boat for you zul8tr. the boat is true all the way down but it seems to have a little bit of hook 6in from the transom maybe of 1/8 of an inch. I also have what I think you call an "ice runner" down the middle of the boat, I wonder if it creates any type of a disturbance in front of the prop. I measured along the width of the boat and starting about 3 feet from the transom, the boat becomes a flat bottom with no vee at all. Also my yard stick was the longest straight edge I had and checked it with a laser, it is truly straight. Well here ya go...

5476654767547685476954770

[zul8tr]

Here's some pics of the boat for you zul8tr. the boat is true all the way down but it seems to have a little bit of hook 6in from the transom maybe of 1/8 of an inch. I also have what I think you call an "ice runner" down the middle of the boat, I wonder if it creates any type of a disturbance in front of the prop. I measured along the width of the boat and starting about 3 feet from the transom, the boat becomes a flat bottom with no vee at all. Also my yard stick was the longest straight edge I had and checked it with a laser, it is truly straight. Well here ya go...

5476654767547685476954770

The attachments do not open?

[omcstratos]

Here's the pics, refer to my above post for the text. I've edited this one too much to get the pics right

[Master Oil Racing Team]

That riveted V will cause an air tunnel. I have seen it happen with an SK fin mounted several feet in front of a Merc speedmaster lower unit. The front of the SK fin was sharp, but the backside was totally flat. 90 degree flat. So that let an air slip develop. The faster we went the further back the air hole slipped until at 70 mph the air hole connected with the water intake holes. This speed higher than what you are experiencing, but that open holed "V" runner in front of your prop will disturb the water. It might not make any difference, but you could mix up some good epoxy....shove it up into that vee, and hammer it closed from both sides. Make the trailing edge come back together. We solved our problem by grinding the back side of the SK fin so it was sharp also. That made the water close back in behind the fin. That fin was not made for what we were doing, but after experimentation it made all the difference, and that's what testing is all about.

[zul8tr]

Good tips from Master Oil Racing Team, do them. The hull is a flat bottom with runners on the bottom that definately will affect speed and water feed to the prop and were placed there to stiffen the bottom, usually they put those on the inside but maybe they wanted extra protection on the bottom for beaching, etc? Plus the hook is just enough to push the bow down at speed and removing it would help. These small alum jon boats do not really have speed designed into them so you definately have a challange to get to 50 with that engine. Because this hull has very little aero lift and some very small amount of air compression under the hull to help lift all your speed gains will be related to reducing water drag which is far greater (about 780 times more that air drag if density is the only varible changes). You can reduce some water drag with a higher engine height if you can keep the prop pushing, but hull drag is another matter that will come about by lifting the bow so the hook removal will help here and getting rid of depressions and bumps in the last 4 to 5 feet of the bottom. Hook can be removed with epoxy thickened with cabisil (fumated silica) and leveled on to the correctly prepped alum bottom. But before doing this do the Master Oil items then fool with the next prop Ron is sending then clean up the hook and bottom irregularities still be prepared to fool with other props.

[Ron Hill]

My dad had a Rocholt Runabout, and he played with bottoms at his cottage at Lake Elsinore. By the time I was old enough to walk, I was told flat bottoms, sharp trailing corners were very important. Earl Bentz wrote a book about Performance improvements, it could have been written by my dad.

This aluminum boat's bottom actually caused me to have a "Nightmare" last night!

[omcstratos]

This aluminum boat's bottom actually caused me to have a "Nightmare" last night!

Its not that bad is it!?

[Master Oil Racing Team]

I got to thinking about my advice, and thought....that is probably the hole to drain the boat. And I said to epoxy it up and hammer the ends closed. I was thinking of higher speeds for the boat and not the drainage. There seems to be maybe a drainage hole to the starboard, but it's hard to tell. I noticed though in the pictures that there had been a lot of extra riveting in the bottom ahead of the transom. If the V is not needed, then I would suggest as I did before, fill it in and hammer it shut.

[Gene East]

Its not that bad is it!?

Perhaps not for a john boat intended for fishing, but for a racing application, YES IT IS!

Your straightedge clearly shows a hook of about .100 inch. When I was actively involved, Pro-division racers strived for totally FLAT (.000 to.010 inch hook or rocker) with sharp edges at the transom.
BTW: A highly polished finish did NOT seem to be an advantage as long as the sanding was done fore and aft. Never cross ways!

We achieved this flat bottom when I was racing by hand sanding with a glass foam insulation block commonly called a "stink block" because of the sulfur smell emitted while sanding with them. I was too hard headed to wear gloves while sanding so during the racing season, I never had fingerprints. Probably would have made more money cracking safes than racing boats.

In addition, it was not uncommon to haul flat bottom boats upside down or on the side.

Achieving a totally flat bottom on a welded and riveted boat is nearly impossible.

I agree with Wayne on reshaping the hollow runner down the middle of the bottom and since it is my understanding that you are a drag racer and turning probably isn't a big deal, you may want to consider shortening the length of this runner just a bit to allow the water to re-merge even earlier. However, bear in mind this runner also stiffens the bottom and you already have a hook.

If you do trim the runner back, DON'T GET CARRIED AWAY!

Good luck!

[Ron Hill]

Perhaps not for a john boat intended for fishing, but for a racing application, YES IT IS!

Your straightedge clearly shows a hook of about .100 inch. When I was actively involved, Pro-division racers strived for totally FLAT (.000 to.010 inch hook or rocker) with sharp edges at the transom.
BTW: A highly polished finish did NOT seem to be an advantage as long as the sanding was done fore and aft. Never cross ways!

We achieved this flat bottom when I was racing by hand sanding with a glass foam insulation block commonly called a "stink block" because of the sulfur smell emitted while sanding with them. I was too hard headed to wear gloves while sanding so during the racing season, I never had fingerprints. Probably would have made more money cracking safes than racing boats.

In addition, it was not uncommon to haul flat bottom boats upside down or on the side.

Achieving a totally flat bottom on a welded and riveted boat is nearly impossible.

I agree with Wayne on reshaping the hollow runner down the middle of the bottom and since it is my understanding that you are a drag racer and turning probably isn't a big deal, you may want to consider shortening the length of this runner just a bit to allow the water to re-merge even earlier. However, bear in mind this runner also stiffens the bottom and you already have a hook.

If you do trim the runner back, DON'T GET CARRIED AWAY!

Good luck!

If you search for John Peeters on Facebook, you'll see how a six straight Nationals Champion is OSY 400 flattens a bottom.

John's mother is my cousin.....His dad learned bottom flattening years ago!

My dad would keep my boat upside down, within 30 minutes of race time, and hit it with a "Stink Block" just before the race. As we found, coming from California where the are is dry, racing in humid climates caused our transoms to swell, and a 1/16 cold and would cost you a Nationals.

.125 inch lip (hook) in the last 1/8 of the bottom, will keep a boat from planing. I once told a guy how t glass his bottom with masking tape. He pulled the tape without sanding the bottom, the "LIP" where to masking tape was, kept the boat from planing,

[Fastjeff57]

...".125 inch lip (hook) in the last 1/8 of the bottom, will keep a boat from planing. I once told a guy how t glass his bottom with masking tape. He pulled the tape without sanding the bottom, the "LIP" where to masking tape was, kept the boat from planing, "

Due to prop cavitation?

Jeff

[omcstratos]

I have a little improvement from my last prop test. I finally broke through into the 40s. The 12.5 x 22 with the extra inch of diameter seems to really respond better. Holeshot has dramatically improved and so has "grip" in the water. The previous prop felt like it had excessive slip.

Max rpms are 4800, 2.42 gear ratio, 22in pitch, and 40 mph. This calculates to 3.2% slip according to the calculator Zul8tr uses. Hard to believe it is that low. I think maybe a 20" might work better maybe?? I'd like to run 5500 to 6000 not to lug it.

It is just a fishing/hunting boat so I will be happy if max speed is in the mid 40's. (much better improvement than 28mph with the original 13pitch aluminum when It was first given to me)
Oh, I also raised the motor up a lot higher with the better grip. Found my max height before water press drops off.

Next step,,, flatten out the bottom with the epoxy and try out a 12.5 x 20 I suppose..

[Ron Hill]

I don't have any 20's, right now....but I probably should make some. Keep us in the loop....

[omcstratos]

I may try a transom pickup and get the bullet of the gearcase up out of the water more. I don't want to put a nose cone lwp on and create more drag if I can't run at a high enough elevation.

[fs5]

hi mate,see if you can get a good prop guy to cut a bit of diameter out of it and trim some off the blades.
sounds like a 12inch d prop would suit you better.maybe even a 11.5?

[omcstratos]

hi mate,see if you can get a good prop guy to cut a bit of diameter out of it and trim some off the blades.
sounds like a 12inch d prop would suit you better.maybe even a 11.5?

I think I need the extra diameter, the 11.25 I tried before didn't work as well

[omcstratos]

If you search for John Peeters on Facebook, you'll see how a six straight Nationals Champion is OSY 400 flattens a bottom.

John's mother is my cousin.....His dad learned bottom flattening years ago!

My dad would keep my boat upside down, within 30 minutes of race time, and hit it with a "Stink Block" just before the race. As we found, coming from California where the are is dry, racing in humid climates caused our transoms to swell, and a 1/16 cold and would cost you a Nationals.

.125 inch lip (hook) in the last 1/8 of the bottom, will keep a boat from planing. I once told a guy how t glass his bottom with masking tape. He pulled the tape without sanding the bottom, the "LIP" where to masking tape was, kept the boat from planing,


...".125 inch lip (hook) in the last 1/8 of the bottom, will keep a boat from planing. I once told a guy how t glass his bottom with masking tape. He pulled the tape without sanding the bottom, the "LIP" where to masking tape was, kept the boat from planing, "

Due to prop cavitation?

Jeff

Is it due to cavitation??

[HGipson]

I've got the BRP Etec 60 2 cyl on a semi/flat bottom aluminum War Eagle all welded boat. Cav plate is sitting around 1/2" or so above the bottom. I got my hands on a 13.5 X 23 old OMC drag over hub prop that belongs to one of my buddies. Ran 43 mph the other day. I want to try one of Ron's 12.5 X 22 semi cleavers over hub or thru. and see how it does. Gear ratio is 2.67 which is horrible but I don't think anything else can be done to it...yet. Here's a pic of setup5486654867

[Riverrat001]

I've got the BRP Etec 60 2 cyl on a semi/flat bottom aluminum War Eagle all welded boat. Cav plate is sitting around 1/2" or so above the bottom. I got my hands on a 13.5 X 23 old OMC drag over hub prop that belongs to one of my buddies. Ran 43 mph the other day. I want to try one of Ron's 12.5 X 22 semi cleavers over hub or thru. and see how it does. Gear ratio is 2.67 which is horrible but I don't think anything else can be done to it...yet. Here's a pic of setup5486654867

I have a 12 1/2 x23 over the hub ron hill prop I'll sell you for $300

[HGipson]

I have a 12 1/2 x23 over the hub ron hill prop I'll sell you for $300

Do you have any pictures of the prop?

[Riverrat001]

Do you have any pictures of the prop?
I can email you some or text them to you. I also have a 12x23 merc cleaver for $500

[Riverrat001]

Do you have any pictures of the prop?

I tried to send you some pics to the # you sent but that # won't work