Wow, I haven't tried to read this whole thread, but I see that you came to the wise conclusion that you are severely underpowered and all the prop tweaking in the world isn't going to change that fact.
prop is probably close and maybe even overpropped. I plugged in you numbers into boatdiesel's prop calculator and used a 13" diameter and it gave me a 7" pitch
as opposed to your current
And why would you want to change from a 2 blade
to a 3 blade
prop? Gerr tells us that 2 blades are more efficient that 3. The only reason people use 3, 4 or 5 blade props is to fit into the prop aperture. If you can fit a 13" prop then stick with a 2 blade
, particularly as it is severely undersquare right now.
And finally back to your original premise- improving efficiency by overpropping. You will never be able to measure the fuel consumption
impact on 10% overpropping. If you had enough power to start with, you might overprop 10% and move from 0.06 gal/hp hr to 0.055 gal/hp hr at the same speed through the water
and running 200 rpm
less (look at the specific fuel consumption
cuirve for the Yanmar). You might save a gallon in 20 hours of motoring. It will take a long, long time to pay for an new prop at that savings.
Overpropping only makes some sense when you have much more horsepower than you need to reach hull speed
and you don't ever want to run at hull speed
. You currently have about half of the hp needed to make hull