[Jakeellington]

I have a 8hp High Thrust on a 15'4 Riverhawk classic. I know high thrust means the motor is geared different. The motor was the kicker on a 23 sea hunt. The prop on it now look sto have a very low pitch.....what prop should I get fo best performance with the boat and motor??

 

[Brett]

13:38 gear ratio on your outboard, standard is 13:27.
Hi-thrust designed to push a hull at displacement speeds.

 

[Jakeellington]

Is there not a Prop that can help with this or am I just screwed...I thought I knew alot about boats, am I going to have to sell this motor or change the lower unit?

 

[Brett]

Let's see here...

5500 rpm is middle of max rpm range for the 8 hp...13 x 5500 / 27 = 2648 13 x 5500 / 38 = 1881
so for the 13:27 the prop turns 2648 rpm
on the 13:38 the prop turns 1881 rpm
so a 9 inch pitch blade on the normal motor has a theoretical travel distance 1986 feet per minute.
To equal that the hi-thrust would need a 12-1/2" pitch prop.

 

[Frank_Sebastian]

This is what I think and only an untested guesstimate.

If it is a Yamaha, you may be able to get a prop that will be good enough. I use a 9.9 Yamaha Hi-Thrust on a bait skiff and it will plane a 16' boat that weighs 400#. I bought the aluminum prop from Solas. It was about $75 4 of 5 years ago.

For a more ideal set up for higher speeds you would likely be better off to trade engines. I am not familiar with the boat you mentioned. If it is like the Gheenoe classic you aren't going to get much more out of that engine with a faster prop. If is is more the size and weight of a hisider then you may benifit from a different prop and especially from a standard thrust lower unit.

Please post back and let us know the outcome of your situation once it is resolved.

Best regards,
Frank_S