SS or Aluminum prop?

[SnookHunter]

I have a 16' 2005 Lowe Sea Nymph, with a 2005 Yamaha 25hp 4 stroke. I currently have a Michigan Wheel 9 7/8x 10 1/2. I put a jack plate on the boat because the motor was mounted to low and water would spray up the back all over the motor. I mounted the motor so that the AV plate was even with the bottom of the boat. The jackplate has 5 inches of setback. Well the boat was porpoising like crazy at any trim setting requardless of where I put most of the weight. So I installed a set of doel-fins. That took care of the problem. But the doel-fins were running under the water a little bit. I have now move the motor up roughly 1.5 inches from the bottom of the boat. Now my fins run on top of the water. My problem now is with the motor 1.5 inches higher and the boat load full the wot rpms are 6310 and 6370 with a light load. With the av plate even with the bottom of the boat the wot rpms maxed at 6170 with a light load and 6100 with a full load. Speeds also went from 25mph to 26.5. The rpms were read with a tiny tach and gps verified the speed. My question is can anyone reccomend the correct size prop to put me in the proper range? Would aluminum be ok and net me any performance? Or is SS the way to go performance wise? Thanks in advance

 

[troypolla]

Re: SS or Aluminum prop?

If you go up in pitch your rpm will go down I think its about 100 rpm for every inch of pitch increase.

 

[SnookHunter]

Re: SS or Aluminum prop?

Thanks for the reply. Would a Solas 10 1/2x 11 SS prop help me out any or should I go bigger?

 

[Crownie2]

Re: SS or Aluminum prop?

Are the max rated RPM's 6,000?

If so, I think you may be better off with a 13" pitch.

Bob

 

[SnookHunter]

Re: SS or Aluminum prop?

Thanks Bob for the reply. Yes the max rated rpms are 6000. Would SS offer better performance than aluminum?

 

[Crownie2]

Re: SS or Aluminum prop?

Yes, I'm sure it would but all things are relative.
The increase in diameter would help you also, IMO.

Bob