You have to go about this somewhat scientifically, with heavy emphasis on SOMEWHAT..
ALL work requires horsepower.. You are working with a given amount of horsepower, let's say 40.Throwing water up into the air is work. Pushing a boat forward is work.
If you are working with 40hp, how many will you use to push the boat forward and how many to carry the bow, how many to throw water in the air? The more you use to carry the bow, the less you have left to push the boat forward. If you can make raising the bow a function of the propeller, it uses less horsepower from the motor.
Rake=bow lift
The best possible speed you will push any boat is with the outboard trimmed up 3 degrees positive. And yes, there is a tool to measure the trim angle at WOT, I have one.
Most 40hp motors, 2 or 4 stroke, 2 or 20 cylinders, will push the average aluminum boat about 34 mph. That is average.
First you need a tach. Without a tach, it is all a guess. That motor, if stock, will make the most horsepower and torque right at 6000 rpm. The port mapping in that motor does not lend itself to high rpm.
You are throwing so much spray because your motor is so high on the transom. If you want to run your outboard that high, you need a large diameter prop. The PowerTech SRD is a 11.5" diameter prop, most others are 10.25" diameter. The SRD has 20 degrees of rake, which gives ample bow lift.
My guess is that the prop you have now has cup added, that's why you can run it so high.. Cup holds water on the blades longer. The longer you hold water on the blade, the less efficient the propeller. That works great for running the engine high, but not so much for speed.
If you could give me more specific data, such as WOT rpm, prop pitch, gear ratio, I can tell you how much slip you have. The secret to going as fast as that engine will push that boat is to get the slip to a manageable number.
IF you can turn a 13 pitch prop 6000rpm with 8% slip, you should run right at 37mph and still have a good hole shot. Once you determine which prop design works best on your rig, then you need to play with different pitches to determine the best compromise for YOU between hole shot and top end. There is no magic prop that does both well.
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