prop slip calculators and boat speed calculators

[horizonlawn]

I've been doing some playing around with different props and motor heights on my pontoon with a 150 yamaha, i did a boat speed calculator and it seemed way off, based off my speed it said my boat weighed 5200 lbs, and its only a 225 tritoon, i know prop slip plays a role here also, but im only at 8%. do the speed calc. not apply to pontoons or am i missing something, it said at my weight, roughly 3000, prob. on the high side, i should get 52 mph, i know i wont see that, but i'm way off at 37 mph.

 

[MH Hawker]

Re: prop slip calculators and boat speed calculators

Those wont work with a pontoon type of hull those are for a plaining hull a toon is a displacement hull. So its brute power. Even if your running a tri toon with strakes. That works a lot better but in the end its still brute power.

From what I have learned motor height is not as critical on a toon because of the turbulence around the pod deeper is often better because its in cleaner water, yes it may have extra drag but you get a lot less prop slippage, Like tilt and trim, thats more or less usless. Its only nice to have when your idling up into a shallow area but for adjusting how the boat plains out not so much.

In the end you drop the motor deep enough not to slip when trimmed down on turns, and set the WOT rpms with the prop, Then open a cold one lean back and enjoy the ride.

Hope this helps and I am sure those more experances in this will chime in.

 

[Bamaman1]

Re: prop slip calculators and boat speed calculators

You need to set the height of your motor properly or you're wasting your time fooling with props. You didn't say what your boat brand and equipment is. You want the engine to be low enough but not too low that it plows thru the water. My motor is in the 2nd notch--about 3/4" above being flat on the transom.

If you're running a 150 Yamaha on a 3000 lb. boat, 37 mph is not unreasonable. It depends on your rpm's. My tritoon with a Yamaha 150 is running 41 mph with a 15 pitch Reliance prop @ 6000 rpms. The last 200 rpms were slow in coming, however. I previously had a OEM 14 pitch prop, and it was easily over-reving @ 6200 rpm's and 36 mph.

 

[Rancherlee]

Re: prop slip calculators and boat speed calculators

I agree, getting 40+mph out of a 150 on a toon is tough work. Hell, a 3000# mono hull boat won't reach much past 40mph with a 150 on the back. Strakes make a big difference on a tritoon, there are 2 almost identical tritoons by my grandparents house with Suzuki 250's on the back. The one without strakes runs low 40's, the one with strakes will tickle 50mph under ideal conditions. Under skinning helps alot on tritoons also, with the logs so close together water gets force up and catches the crossmembers.

 

[craigmack]

Re: prop slip calculators and boat speed calculators

I'm reading 40 MPH on the speedo @ 5500 RPM but I'll need to GPS it to get the true speed; I figure it's closer to 37/38 MPH. The last time I compared the speedo to GPS it was off by 2... 33 speedo vs 31 GPS (Alpha 4 prop 15" x 16P).