engine height & prop

[B.D]

I have a Smokercraft deep V which I recently purchased. 100 HP merc. The guy I bought it from said he raised the engine so he had less cavitaion problems. After reading some of the posts I decided to see where my motor height was from the bottom of the V, to the cavitation plate, he has it mounted as far up as it will go.

Cavitation plate 2" above bottom of boat, shouldn't it be closer to 1" below or above the bottom?
How does this high height affect performance? Should I lower it?

Also the motor came with a S.S prop 13 X 17 seems to work well but never got a change to check rpm's as tach was not working. Top speed on my gps was about 36 mph.
I put on the extra prop he had 13 X 19, experienced a lot of cavitation, poor hole shot and top speed of 30 mph. Also the tach is now fixed and my top rpms where only 3800. I was lead to believe that the higher the pitch the more speed and less power.

Over all what's the deal, low rpm's because of high transom height? Just stick with the S.S which preformed well and a fairly good speed and what about the motor height?

 

[jmburock]

Re: engine height & prop

Your RPM at WOT should be around 5200 +/- 200. I would consider going down to a 13 x 15pitch to get your RPMs up. Sounds like the 13 x19pitch is useless for this boat. It would help if we knew what year your motor is.

 

[diaric]

Re: engine height & prop

its best to ask these issues in the prop forum. when they are trying to get the best out of a setup, they will usually try to raise the motor till they get cavitation problems. as they raise it, they will usually gain rpm and speed. but the setup may not work for another prop.putting on the 19 pitch, is like throwing an overdrive gear on your motor. but since its a boat it has too start in that big gear and sure it could go faster but your engine does't have the power to get there, it just bogs out.