If you decide to go to 16* from the PYI recommended 18*, you will be on the
safer side. Just be careful not to exceed recommended Max continuous RPM.
You will not damage the engine by overloading i.e. making the engine “lug”.
You will get less power (12%) from the prop and less speed into head winds and seas.
A good yardstick for comparing relative power from several props and/or prop settings
is as follows: diameter squared times pitch. This is proportional to the
volume of water moved in one revolution. I.E. the size of the block of Jell-O carved
out by one revolution ! :>)
In your example, 4096 versus 4608 yielding .88888, hence my figure of 12% less power
at 16* pitch.
Generally, I prefer to classify props by their actual pitch in inches of advance rather that
pitch as measured in degrees by the calculation above works as long as one is consistent
in the values used for each prop. As you may have gathered from other info on props, diameter
carries more weight than pitch. Maximum diameter useful on any given shaft setup is
determined by blade tip clearance. Dave Gerr’s book on prop selection emphasizes this.
I thought your comments about the Maxi Prop quite interesting as we were considering what to do with ours. We have an Auto Prop, original model which we are generally pleased with except when in reverse. We are considering a change to a Vari Prop. I would be interested in your thoughts on both props and general comments on prop selection for the Nonsuch.
I stayed with the 16 degrees as that was what the previous owner used and the boat performed well under power during the sea trial, reaching full RPM without smoking.
On my pervious boat, a Freedom 45, I had problems with the PYI recommended setting as it did not allow the engine to reach full RPMs. So I know that lab calculations do not always work in the field.
“Big Easy” is finally back in the water. Mast gets stepped tomorrow.