Thanks!
If you are just out for max speed with no load other than yourself in that small boat, max pitch/min diameter without loading down the max RPMs is the thing, but you can end up with too much pitch and it will start loading the motor down. Best to get a tach and check RPM with the prop you have first. Best to run near or slightly above manufacturer’s max rated RPM for max speed. I have a 1976 35 HP Johnson (essentially the same motor up have) on a lightweight, 1957 12′ Crestliner Commodore12, decked aluminum runabout that I drive sitting at a steering wheel in front. I tried a 15 inch pitch and had to back off to a lower one because it performed bad when I had a passenger or two along; and even when alone in it, with the lower pitch prop, I liked the way it did acceleration recovery after it slowed some (or I slowed it some) when taking a quick, tight corner – it was slightly slower on top end, but a lot more fun to drive.
For max speed, (you probably already know this), Shim the motor up higher on the transom using paint stir sticks under the transom clamps until you get so high that the prop starts to lose it’s grip in medium waves, then take out one stirstick – you can usually gain 1 to 3 MPH that way – I check speed on my boats with a portable GPS unit. The lower the motor sits in the water, the more the lower unit behaves like a big club being dragged through the water. AS you do this, adjust the trim pin angle as high as possible without it bouncing at wide open throttle – this will lift the boat up for least drag of boat surface in the water, but too high, it can bounce and it will cavitate on tight corners – I like to live with a bit of cavitation on corners as long as it’s not bouncing on the straightaway. Remember that the less boat in the water makes it harder to handle,so be sure you learn the boats limits in various waves at various speeds. I grew up doing everything you shouldn’t in a boat back inthe late 1950s/early 1960s, and I don’t recommend these setups unless a person is willing to take things easy until you learn the limits of your configuration – these things can flip.
On your model motor, you will not find a super selection of available props, as it is not a popular racing motor. A 2-blade prop will also be faster than a 3 blade, but good luck finding one! Maybe Michigan makes one.
Have fun!
Dave
Below is my son and daughter in that boat with my dog who loves boats:
