Prop question and Help

[Raw Seas]

I had a 1997 26ft. Striper walk around with a 225 Johnson ocean pro on a bracket using a 15 1/2 X 15 aluminum prop.
seemed well suited.
Recently upgraded to a 300hp ETEC with an SS Apollo 14 1/4 X 19. Numbers appear to be correct for new motor and prop, WOT 5700rpm, top speed 32 mph, but....................

Boat handles differently especially backing up, mush less control now
Smaller motor got up and kept on plane at 3700rpm., now I must maintain 4300rpm's to stay up on plane.
Also getting cavitation while accelerating, rpm's bouncing up and down on the way to that sweet spot.

so my question is would I benefit from getting a prop that more closely resembles the original prop.
Thanks

 

[jimmbo]

This Apollo prop, 3 or 4 blade?
Comparing Rpms between the 2 engines is rather pointless, as they likely have different gear Ratios and the props are different pitches.
It's on a bracket
AL props are inexpensive, you could try one.

 

[dingbat]

You lost a lot in the diameter change. Guessing a 15.5 x 17 would get you back in the ball park.

Found an interesting discussion on propping your boat with an F300 but will not allow a link....

Mercury Revolution 4

40 kts. at 5700 rpm
33kts at 4400 rpm - cruise

 

[Maped]

When you say cavitation and seeing the rpm bounce are you sure that you aren't breaking the water surface with the prop and ventilating? Have you verified your motor height since installing the new one?

 

[dingbat]

I had a 1997 26ft. Striper walk around with a 225 Johnson ocean pro on a bracket using a 15 1/2 X 15 aluminum prop.
seemed well suited.
Recently upgraded to a 300hp ETEC with an SS Apollo 14 1/4 X 19. Numbers appear to be correct for new motor and prop, WOT 5700rpm, top speed 32 mph, but....................

Boat handles differently especially backing up, mush less control now
Smaller motor got up and kept on plane at 3700rpm., now I must maintain 4300rpm's to stay up on plane.
Also getting cavitation while accelerating, rpm's bouncing up and down on the way to that sweet spot.

so my question is would I benefit from getting a prop that more closely resembles the original prop.
Thanks

your way under propped. 5700 @. 32 mph is 30% slip

 

[QBhoy]

Probably shouldn’t compare two different engines for prop sizes. Be different ratios likely.
Witth this there also maybe a chance your new engine isn’t set up right for height ? Is it ?

 

[Raw Seas]

TY all
taking it out next week to clean bottom, recheck height and try a new wheel