I/O prop question

[Wingedwheel]

I've got a '96 SeaRay Signature 190 with a 4.3L and alpha one outdrive. I'm currently running a 14 1/2x 19p SS. I took her out today and did a couple of tests. I installed my spare, which is the same prop in aluminum. Running at WOT with 3 people in the boat I was turning 5000rpm's and about 40mph. I switched back to the SS and ran around 5500 rpm and 44 mph. My question is does this sound normal? Also, what would I gain by dropping to a 17P to pull skiers? Thanks in advance guys....

 

[steelespike]

Re: I/O prop question

Its normal for props to perform differently especially going from al to ss.
Results can vary unexpectadly.
rpm can vary as well as speed.certain ss might be lower rpm and viceversa.
My info indicates your max rpm rating is 4,800 So your way over with you ss prop.
With that setup I would expect you might be over.You should avoid this.
Your hole shot should be good but its possible the ss prop may not do well with hole shot dependong on its design.A 23" prop should put you closer to 50mph.
and get your rpm close to that required.It likely won't do as well for sking.
A 19" 4 blade should work well for skiers.You still may have to watch your rpm.

 

[Wingedwheel]

Re: I/O prop question

Thanks Steelspike. I'll look into a 4 blade. The SS I have is a 3. I just wondered if a 17p would lower the rpm's because I know it would decrease the speed, correct? The factory recommends the one I have, but I understand its a general use.

 

[tgell001]

Re: I/O prop question

It would have the opposite effect, it would raise the RPM's and lower the speed. Think of the prop as the rear end gear on a car. You raise the mechanical advantage (lower pitch/higher gear ratio) you get more torque (launch) but the consequence is a reduced top end. Youre probably designed to run a 21p prop and you'll be in the high 40's in top speed. Personally i went from a 3 blade 21p to a 20p 4 blade and only lost ~3mph and gave myself a huge advantage out of the hole. I'm a big fan of 4 blades after I purchased one. Not only did it do what i wanted for wakeboarding w/o loseing all my top end but it also made my low speed idle smoother because 4 blade props are more balanced. Good luck with your search, honestly go to the prop shop and ask the people working there. You'd be suprised how much experience they have with boat specific applications.