Quote Originally Posted by chris3298 View Post
Made two runs to the river today, First run I had the new Tohatsu tach hooked up and now realize this I'm checking the rpms with the motor raised just one bolt hole and my rpm's were about 5300. Second run I then went back home raised the motor to the third hole and was able to then get a solid 5400 rpm's maybe a spec more, Cooling was fine I kept looking back to make sure and it was good. Did notice two little cool rooster tails shooting upwards off the cavitation plate.

I really didn't notice any drop in speed going up to the third hole although didn't have my gps with me. I did notice looking back though there wasn't as much as a wake like before when I was only up on the second hole. Didn't hear any sounds like the prop was cavitating or anything.

I think I can go up to maybe the last hole but will really have to watch and see if it ends up sucking air and loosing water pressure, thought about putting a piece of tape at the top to holes even though there not open just to make sure it doesn't suck any kinda air.

I realize now a Jack plate is probably better at this stage I could probably run a little higher then on the last bolt hold and still be having good cooling and hopefully more speed

What you guys think? try a jack plate now? or go up to the last hole?

The motor needs to run at 5850 is what the manufacture says I was told it may even run a little higher that around 6100 is probably when the rev limiter will kick in.

prop used is 11x14.1 almost like i need to go down in the number which don't want to I want to go faster.
If your tach is accurate first go up higher w/o jack plate (less costly approach) and note the rpm results bring the GPS so speed is measured , w/o that results are not complete.

If still below the rpm target you need to go to less pitch. Less pitch does not necessarily mean less speed because the rpm is increasing.

based in your numbers if rpm is 5400 then your est speed with no slip
= 5400 x 14/(1.85 x1056) = 38.7 mph
if you had GPS speed slip can be calculated

Example if pitch is reduced to 13 and rpm can get to 6100 with jacking and trim (just an example) then;

estimated no slip speed = 6100 x 13/(1.85 x 1056) = 40.6 mph, up a bit

Note these are made up numbers but you get the idea.

Test and take notes on gps speed and rpm so we have a solid point of reference to calc slip and other.

There might be some benefit to reduce the diameter and keep the pitch but if the hull is heavy this will go against you to plane especially if water skiing is to be done. For pure straight line speed runs the smallest diameter and largest pitch that will plane the boat, reach the rpm and max speed target is what you want. However the boat may not turn worth a crap, so you have to decide what you want. There is only so much you can extract from the boat and motor for the hp and weight that you have.