New motor on old boat

[Supersportster]

Hello...

At the end of last summer I switch out my 89 Johnson 90hp for a 98 115Hp Johnson fast strike.

My boat is an 89 Sylvan supersportster. From my research it ways 900lbs plus two batteries and gas and the motor, all in weight around 1400-1500lbs.

The new motor has a 14x 19 aluminum prop, and the boat jumps out of the hole EXCELLENT. I like the hole shot and the mid and top end ride of the engine. The reason for this post is that at wide open throttle with me and one other person I am only at 5100-5200 rpm @ 42mph.

I'm thinking I should be at 5800 rpms with this motor.

My boat store said to switch to a 17 pitch prop? How would this change the hole shot and mid and high end? I am not opposed to going with a stainless steel prop, I just need a better understand of what prop Ishould change too..

Thanks in advance...

 

[steelespike]

Re: New motor on old boat

My unvarified info indicates 6,000 rpm. What is the length of your Supersportster?
Basded on the dry weight I think the 19" would be normal And turn 5500 or more.
This isn't carved in stone because similar aluminum boats speed can vary widely with similar setups. 42 is very respectable at 5200 rpm.Is speed by gps?
Is the antivent plate(just above the prop) even with to about an inch above the bottom?
Measure with a straight edge along the keel.
If you went to a 17 your hole shot would be even better.Probably add 300 to 400 rpm.
Speed about the same.

 

[Supersportster]

Re: New motor on old boat

Steelspike yes the speed is by gps... the gauge on the dash shows more buy a few mph. The boat is 18ft, the canadian ownership says 17'8.

The plate is just above the bottom keel, but I have to measure exactly..

Do you think I should go to a stainless steel 17, or 18?