Prop calculator at:
https://www.vicprop.com/displacement_size.php
May not have any correlation to what is actually installed on your boat. It is simply a starting point. If you can hit max rpm youre in the ball park already.
Thanks for all the input.
I just measured the props and they are 20". The pitch seems to be stamped on the shaft of the prop.
I don't know if these are the original props. I can hit 2850 rpm but the most speed I have gotten is 13 knots. Getting a little vibration on the starboard side. Cutless is in good shape.
I am having the starboard Cat 3116 rebuilt. while the boat is pulled I want address any issues that require the boat to be out of the water.
Diameter is a relatively fixed value. The clearance of the Propellor (distance between prop blade tip to hull)should be 15% - 20% of diameter. (Ideally 20% or more).
Once you have the diameter, the Pitch is calculated, by and large, as a result of Max RPM. Theoretically, if you can exceed the max rpm, your underpropped (pitch needs to be increased). IF you cannot reach max rpm, you are overpropped (pitch needs to be decreased).
This is a loose rule of thumb to which there are many opinions. Tuning is somewhat of a dark art IMHO.