Need propeller help (odd testing results)

Hello all and thanks in advance for your assistance.

I have a 1989 Rinker Captiva 206 Bowrider best guess on GVW is 3300#

Engine: 5.7L 4bbl carb guessing HP around 250, Recommended revs at WOT 4200 - 4600 (I think)

Outdrive: Alpha one, gen one I think it has a 1.50 gear ratio (but am not positive)

Came with a three blade MERC 14x21 aluminum prop (great condition)

Tested at typical load: WOT - 4575rpm GPS speed - 49mph

I wanted to get a little better pulling and midrange economy so I did some research and tried out the Piranha four blade 20 pitch propeller.

Tested at typical load: WOT 4100rpm GPS speed 44mph

Seemed to pull just a little better and was certainly faster to plane but due to under reving (and what seemed to be very excessive fuel usage), I sent to get the 18p blades

Tested at typical load: WOT 5100 GPS speed 37mph

Now I am not exacly sure what happened here. Every test was done trimmed out. I tried several times with each propeller very close results each time. What the heck?

More importantly, what now? My thought is to get a solas four blade aluminum 21 pitch. Would this give me better pulling and mid range without under reving? What about just getting a 21p three bladed solas for a backup?

If I went stainless, what should I go with? 3 or four blade? what pitch?

Thanks again for your assistance.

Re: Need propeller help (odd testing results)

the 20 was too much, the 18 not enough..sounds like it is crying out for a 19P. 4 blade...if it was my boat I would put the 21P 3 blade back on and get a set of trim tabs. a 21P 4 blade is going to be way low on RPMs

Re: Need propeller help (odd testing results)

SparkieBoat said:

the 20 was too much, the 18 not enough..sounds like it is crying out for a 19P. 4 blade...if it was my boat I would put the 21P 3 blade back on and get a set of trim tabs. a 21P 4 blade is going to be way low on RPMs

Click to expand...

The 19P four blade may be worth a try. Theoretically, the 20p four blade should have hit the sweet spot by all the numbers I read.... but that didn't quite work out. Could it have been the composite?

I would LOVE to put on trim tabs but unfortunately, my molded in swim deck won't allow it. I talked with Greg at Nauticus and sent him a picture of the back of my boat. There is just no way it can be done (cost effectively). I did put on a hydrofoil (SE Sport 300). That helped the holeshot a good deal. I was hoping to be able to bring down my rpms at tubing and ski speeds for economy. I would like to have a spare propeller on board and was hoping that I could get some other desireable function out of it as well. I will definately keep the 21p. Perhaps it is smart to just buy another one (solas?) and call it good... It's not like it is a dog or anything. It performs well and is a good all purpose prop. However, the other part of me keeps thinking "but maybe it could be better"...

Re: Need propeller help (odd testing results)

I would not get composite, get alum at least..I prefer SS