Pirhana Props = No way!!

[Speedtek]

Here's the deal. I've had a 19' 1988 Bayliner cuddy with a Force 125 hp engine. There's been a number of problems with it, but no matter what I did, I could not get past 3500 RPM. The boat had a Piranha 3 blade 13-1/4" x 17" pitch pushing it, there was nothing wrong with the prop, the blades were all in good condition ect..

Anyway, after tweaking carbs, checking the timing for the 100th time, checking compression... everything you need to do to make sure the boat is functioning right.... nothing would change the 3500 rpm limit.

I remembered that the boat came with another prop, and aluminum 13x17, but it was nicked up. I filed down the nicks and put it on the boat just for the hell of it.

WOW - I gained 1100 RPM from it!!! The boat was cruising at around 40-45 MPH at about 4600 RPM. It's like a totally new boat.

SO anybody that may be having problems and has one of these props BEWARE - It may be good if you have a low power motor pushing a little fishing boat, but no matter what they say, it will not push a bigger boat right!

The bad part is now I have this extra plastic prop, and I cant even use it as an anchor since its too light. Oh well, live and learn right??

 

[hwsiii]

Re: Pirhana Props = No way!!

Speed, there is something wrong with the assumptions you made about the Piranaha prop, don't get me wrong I wouldn't buy one either because I have a flats boat and I would be breaking blades all the time. But what you are saying is that the piranaha was holding your RPM down, not letting them reach full potential as the aluminum prop is doing. If anything a composition prop should let the RPM turn more than an aluminum prop because of prop deformation in the composite material. There is of course the difference in the diameter between the two props, but it certainly won't make up even close to the 1,100 RPM difference you show between the two. I don't know what is going on but in my opinion either the piranaha is not a 17" pitch, the blade surface area for each prop is dramatically different, or one of the blades in the piranaha is in backwards if that is possible.

H

 

[Speedtek]

Re: Pirhana Props = No way!!

I totally understand your hesitance to believe it. I took it to a local shop and they said the prop was what was holding my speed down. I said "Pfft!" to that thinking I knew better.

I'm positive of the props size and that the installation was right. I've actually read in other posts that people say there's a loss in performance, but again, I did not want to believe it.

But, first hand experience - Piranha prop = 3500 rpm, Aluminum prop - 4600 rpm. Why the difference? I have no clue, could be flex and deformation, but it is what it is.

 

[hwsiii]

Re: Pirhana Props = No way!!

I am not questioning your veracity at all. But theoretically if the prop flexes that means you would have less pitch and thus the RPM should increase and not decrease, at least in my mind. 1,100 RPM is not a loss in performance, it is a DISASTER. LOL
I will just have to chalk this one up to unexplainable in my mind. But I am glad you had another prop and can use your boat.

H