Prop for 14.5" CC w/ 40 hp.

[NascarNHIS]

My question is what prop size and material prop should I use. I just bought this boat and motor. It planes at 15 mph and tops at 30 mph with trim full down, and planes from 20 mph up to 35 mph with trim adjusted. My goal is to lower planning speed, top end is not important. I plan on adding a SE Sport 200 Hydrofoil that I have; I want to make sure I have the correct prop before I add anything

I have a 14.5? Center console (71? beam) V bottom, with a 40 HP outboard.
Model 1975 VIP industries, Seasquirt, Center Console, V hull
Model 1996 ELPTO Tracker/Mercury 40 hp. 4 cyl. 2 stroke
Engine ? 2:1 gear ratio, max rpm 5000-5500
(rpm is from the book I do not have a tachometer to verifiy actual)

Boat weight 525# (dry).
Engine weight 192#
gas, and gear 150-
Passengers 410#.
total 1277 lbs.

Existing prop is
11? (I think 9 ? pitch but no sure, I just measured it) 3 blade
Engine is mounted as low as it can go on he transom and puts he cavitations plate exactly on line with the base of the keel

I have looked for an online prop calculator but all the links I have tried will no run om my computer.

Thanks in advance for any advice.

 

[hwsiii]

Re: Prop for 14.5" CC w/ 40 hp.

Nascar you need to buy a Tiny Tach to check your RPM, they are only about $ 40. You certainly dont have a 10" pitch prop it could only do about 24 MPH, it would require a 15" Pitch to reach 35 MPH, but I am questioning that speed, It is not by GPS is it, but by a speedometer. We could use the RPM to verify what RPM you are actually turning and to figure your prop slip as well.

H

 

[steelespike]

Re: Prop for 14.5" CC w/ 40 hp.

It would appear from your speed that your setup is pretty close.
Is the speed by gps?
If you have no problem with ventilation(cavitation) you may be able to raise the motor a little for a slight improvement in speed and hole shot.
Without your present rpm its difficult to make any prop decision.
A tinytach is reasonable and easy to install.
Foils can be very effective but can create problems.Imagine dragging it through the water. Hard to imagine it imprioving overall performance.I feel something like smart tabs is a better choice.
A 4 blade will improve hole shot and low end performance at a slight
decreas in top end.
The Turning Point Hustler props have close to stainless performance.
And from reports here generally produce an overall improvement.
Also may allow further increase in motor height.

 

[NascarNHIS]

Re: Prop for 14.5" CC w/ 40 hp.

The speeds are by GPS.
I see that i do need actual RPM, and I will get a tach and see what I have.
Thank you for your comments.