Sorensen long haul center fin

**zul8tr** · 07-12-2014

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** · 07-12-2014

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

**champ20B** · 07-12-2014

Originally Posted by 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

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** · 07-20-2014

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?

**John Schubert T*A*R*T** · 07-20-2014

Originally Posted by 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?

That's about the maximum speed that you should expect.

**Yellowjacket** · 07-20-2014

Originally Posted by 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?

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** · 07-25-2014

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** · 07-25-2014

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** · 07-26-2014

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