Pontoon Prop

[NeuGuy]

I have a 22' Tritoon with a 4.3 MPI Alpha One. The Alpha currently has a 15.25" x 15P stock Prop on it. I would like to upgrade but like alot of people in this forum do not know alot about props and what would be best for my set-up. I would hate to spend, my wife would hate it more, a lot of money on trying out new props to see which one would work best. Does anyone have any suggestions as to what would be a good upgrade? I'd like to get some mroe top end out of it...I do about 35mph trimmed on a smooth lake. I would really like to get another 3-5 mph if possible with the right trim and prop. Any suggestions?

 

[roscoe]

Re: Pontoon Prop

Welcome to iboats neuguy.<br />Key to the decision is your wide open throttle rpm, with a light load, and a heavy load on board, and what is the maximum recommended rpm for your motor.<br /><br />It just may be that you are at max speed/performance for your motor and "hull" design.<br /><br />What will 3-5mph do for you, and how much time and money do you want to spend to get it?

 

[NeuGuy]

Re: Pontoon Prop

Thanks for the welcome,<br />3-5 will get me to keep up with the Jones's of course...just kidding. I'm just trying to run as efficiently as possible and as quickly as possible. I settled for the pontoon with my wife, in two years I want a 26' mid-cabin with a "big dog" in the back...something that does about 70+. But for now...I'm new to boating and just want to make sure she's giving me all she can (my boat that is).<br /><br />I went to RBBI Prop calculator...and this is what I got. Using max recommended rpm for my engine of 4800 rpm with a light load..I get 35 mph trimmed, getting about 4750-4800 according to my tach. If I went to a 17p SS prop I would get an extra 4.7 mph out it. <br /><br />So more higher pitch = lower RPM but higher amounts of water being pushed? With that, then I propbably wouldn't get all of the 4.7 mph out of a 17p prop but I would get let's say about 3 mph?<br /><br />Am I even close...I would hate to spend 3 bills on a nice prop but have NO performance increase. I know I should go to a SS prop because they are better...but should I spend the money when my alum. stock prop is doing just fine or would get the same performance?<br /><br />Thanks again!!!

 

[NeuGuy]

Re: Pontoon Prop

One more thing while I'm on the subject of a pontoon prop.... <br />I've been reading alot of threads in this forum and have contemplated buying a 4 blade SS rather than a 3 blade, because of the amount of people we would have on our boat on a normal weekend (5-7 people). The threads lead me to better control of heavier loads and beter hole-shot with those loads. <br /><br />I mean my boat is 3110# dry...gas, people and stuff let's bump that up to about 5000#s or better. Any thoughts?<br /><br />Also, Does the diameter of the prop matter that much? I have a 15.25" x 15p right now...if I was to go 14.5 x 15p x 4 blades...what would that do?

 

[NeuGuy]

Re: Pontoon Prop

It's been awhile since I've posted on this particular thread...but still have a few questions about my prop.<br /><br />I ran into a sand bar this past weekend at the river and really dorked my aluminum prop up. so, an upgrade or at least a new prop is inevitable within the next few weeks. I was looking into replacing my 15.25 x 15p alum. with a same size SS prop. My problem is, I can't find one that has the exact dimensions...I either have to step up to a 15.75 x 15 or something around a 14.5 x 15 or 16p. Any thoughts on what would be a good replacement?<br /><br />Before my I dorked my prop...WOT was right on at 4800...although I did notice alot of loss in performance when I turned I beleive it was cavitating, but not sure I know exactly what cavitation is...I beleive it is when the prop is getting too much air and not biting enough water.

 

[Silvertip]

Re: Pontoon Prop

You said your original prop provided WOT at 4750-4800 RPM which is what the recommended WOT RPM is for that engine. A 17P prop "theoretically" (according to a prop calculator) would give you 4.7 MPH (your numbers not mine). What you fail to take into consideration is that you lose about 200 RPM for each inch of pitch increase. So now you drop RPM to 4400 and speed stays the same. There is no free lunch. The 15P prop was originally installed because that's the prop that places the engine RPM where it needs to be. The resulting speed is what you get. Prop calculators are great, but you need to understand what they are telling you. Prop design can indeed provide some benefit but you need to work a deal with a marina or prop shop to try some to find the one you like. I seriously doubt you will ever get 4 - 5 MPH with prop changes. You are pushing a barn door through the water.

 

[NeuGuy]

Re: Pontoon Prop

Upinsmoke,<br />I understand all of that now...but thanks for the reclarification. What I really need to know now is....if I have a 15.25 x 15P alum and want or need to replace it, I would like to go SS....question: what size should I replace it with? I have read that a SS prop of the same size will drop my RPM by about 200 or so, same as an increase of 1" in pitch...so should I drop down to a 14 or maybe even 13P prop? Also, I've noticed not many SS props in a 15.25 diameter...would it hurt to drop to a 14-1/2"?