[PUP] Overpropping

[Ron Rogers]

I own a 1985 Willard 40 with a Perkins 6.354 whose manual states that it 
should be propped so that it can achieve WOT at 2800rpm. Willard equipped it 
with a 28x18 three-bladed prop. Underway, max rpms was 2550 rpm on an 
adjusted tach. The engine seemed to labor and the engine room was always 
very hot, but the engine ran at normal temperatures, although it came up to 
temperature very quickly.

I changed the pitch twice determining, finally, that 28x17 allowed 2800 rpm 
and I could cruise at 2200 rpm instead of the previous1800 rpm. There is now 
less noise and heat. However, top speed has dropped from 8.6 knots to 8 
knots. I don't care because cruise has been 7 to 7.5 knots and I intend to 
experiment at lower speeds to find the most fuel efficient compromise.

Ron Rogers

----- Original Message ----- 
From: "Patrick Gerety" <alohaboat@yahoo.com>
|
| Willard Marine was founded by Bill Tighe (now
| deceased) back in the 1950's.  Bill was a big fan of
| over-propping.  All the Willard 30's, 36's, and 40's
| produced in the 60's, 70's and 80's were over-propped.
| However diesel marine engines were a bit different
| then and evidently the makers  encouraged
| over-propping to some extent.
|
| I don't encourage over-propping with the marine
| engines that are available today.  The conventional
| wisdom and recommendation of diesel makers today is
| that the engine should achieve maximum rated RPM's at
| WOT under load.