Getting more RPM's out of my outboard?

Mark Vanderhoof

Mark Vanderhoof

Active member
hey guys, i have a 50hp tohatsu tiller on my 16' starcraft. with 2 guys and gear i have sufficient power but with 3 guys its underpowered. tough to get on plane in all but flat conditions. my boat is a big and wide 16 footer and its pretty heavy for its size but it seems like my motor is capable of doing more. a friend has a similar but lighter 16 footer with a 48 evinrude and he planes of with 4 guys. i dont think im getting enough rpms out of the motor. i plan on talking to my mechanic about this but im wondering what course of action i should take to try and improve motor performance? i have 2 other props to try as well. thanks for any tips. best, mark
 
You really want to make sure that your operating within the motor's specified WOT (wide open throttle) rpm range.
Therefore, choose a prop with a low-enough pitch, that even when heavily loaded, you're at the low end of the range. Too high of pitch puts considerable strain on the engine, and often doesn't allow you to achieve the full power capability of the motor.
I'm a bit nerdy with engines, so I installed a tach for my 40hp. I just don't like not being able to see rpm.

View attachment tach.JPG
 
I am no expert but I do read the DHBP eveyday.
Sounds like you need two things: a Tach to make sure you are running in the right RPM range and a different pitch prop. Maybe a local shop will let you test a couple out?
 
A slightly lower pitch prop will help it get on plane. Once you find the best prop, I would send it out to a prop shop to have it cupped. They cup the trailing edge so it grabs more water at top end for higher speeds.
 
I used to have a 17' xpress with a 40 yamaha. What a dog! This boat would not get on plane with 4 people in the summer. I reduced the pitch on the prop, and maximized the diameter of the prop. I went from a 14 pitch to a 11 if memory serves. I seem to remember that the diameter went from a 9.5" to 10.5" or 11". I also seem to remember that for each numerical pitch decrease, your rpms increase by about 200...it has been a while. The larger diameter prop offsets the rpm increase on the top end so you are not redlining. I am not 100% on this, but is best as I can remember. And that 17' xpress with the 40 yamaha would plane out in no time fully loaded with 3 guys, dog, decoys and gear with the new prop. Hope it helps.
 
like others said a tach first, then a smaller pitch bigger diameter prop. If a heavy load is common I would get a prop that puts you 4 or 500 rpm over max rpm and then have a prop shop add cup to the prop until the rpm's are where they should be, this will get you the best bang for the buck without re-powering
 
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