How much HP = How much speed?

[samblane]

I'm looking into re-powering my 1977 Harris-Kayot Commander 28' boat. It's actually a 24 ft. deck on 27 ft (tip-to-tail) 19" pontoons. It currently has a 35hp evinrude with a 10.5" 11 pitch prop. Max speed was measured at 13.9 mph w/GPS handheld.<br /> Main question: What is the highest max speed with a new high HP motor? Unfortunately I don't know the max HP rating of this boat. Do any of you? Assuming it is 90HP (I don't know if that's realistic or not) what do you think the max speed would be with a 90hp motor?<br />Thanks,<br />Sean<br />samblanet2003@yahoo.com

 

[bayman]

Re: How much HP = How much speed?

I don't know the max hp for this boat. If it isn't on the hull where the outboard attaches then it might be difficult to find that out. For safety and insurance purposes you won't want to exceed the max hp.<br /><br />The easiest way to estimate the speed is to see what other similar pontoon boats will do (same weight, same hull shape, etc..) with a certain amount of hp. You can calculate all of the speeds but looking at available data is much easier.

 

[trog100]

Re: How much HP = How much speed?

i could be well wrong here but i assume pontoon boats are supposed to go at displacement speeds and are not intended to actually plane.. <br /><br />with a displacement boat trying to exceed its economical displacemnt speed just wastes gas.. which (i think) is the reason your boat comes with the size engine it does..<br /><br />u might find that doubling your power only gets u another 2 mph and doubles the gas usage.. my 20 ft planing boat probably takes less than 5 hp to do 5 mph.. but something like 60 hp to do 10 mph.. your question aint that easy to answer.. <br /><br />trog100

 

[AJ168]

Re: How much HP = How much speed?

You're pretty lucky getting a 28 ft boat to do 14 mph with a 30 on it. My aluminum 18 ft center console will barely do 13 mph with a 30 hp. <br /><br />I don't really think that pontoon boats are meant to be fast. You're better off staying with the 30, especially with the way that gas prices are today.

 

[Dunaruna]

Re: How much HP = How much speed?

Modern toon boats do plane, but that's with a 220hp I/O spinning a monster prop.<br /><br />Older toons are simply not designed for high speed.