Correct prop size for a 1964 Evinrude Lark 40hp

[SRosaJr]

I've got a question....I own a 17 foot Arrowglass Tri-hull with an 1964 Evinrude 40hp (2 stroke/2 cylinder)electric shift outboard, could anyone get me close to a correct prop size/pitch to use on this type boat? The boat won't get up on plane it kinda plows through the water...SLOWLY.. about 15-20 mph (I get passed by everything!!) and uses an incredible amount of fuel. The motor runs great(doesn't miss a beat) so I hate to get rid of it, maybe I'm expecting too much from this particular motor and need to purchase a larger one or does everything sound right and "it is what it is" .<br /><br />Thanks ~ Sal

 

[JB]

Re: Correct prop size for a 1964 Evinrude Lark 40hp

That boat should be on plane at 15-20mph, SAL. Is that a guess or a measurement?<br /><br />Do you have a tachometer? What is it reading when the engine is wide open?<br /><br />What prop do you have on it now?<br /><br />I suspect that your problem is in engine trim and/or boat balance (bow heavy).<br /><br />Get more of the weight aft. If you don't have power trim set your engine trim so that the engine is tilted slightly out from the "AV plate parallel with the bottom", and be sure that the AV plate is even with or only an inch or so above the bottom.<br /><br />If you have power trim, start her out with the engine trimmed all the way in, then trim her out as she rises up on "the step".<br /><br />Let us know what you find.

 

[SRosaJr]

Re: Correct prop size for a 1964 Evinrude Lark 40hp

Thanks for the reply JB will try the trim thing....it has a bar that you can move the motor in or out with a series of holes. I think it is level with the hull right now. As far as a tach, being a magnito ignition I have not found a tach to measure the RPM....the MPH comes from the speedo in the boat (which may not be very accurate) I just don't remeber my dad's boat using as much fuel as mine and felt faster but I was a kid and really didn't pay much attention to it. He had a Thunderbird Tri-hull with a 45 horse Chrysler. Gonna try her out this weekend.....I'll let you know what happens.<br /><br />Thanks ~ Sal

 

[SeaMasterZ@aol.com]

Re: Correct prop size for a 1964 Evinrude Lark 40hp

hey Sal, Cherry Hill here ... try a TinyTach.com for a tach,