Bertram31.com General Bulletin Board

Re: shafts and props

Posted By: Rich H
Date: Friday, 11 March 2005, at 12:05 p.m.

In Response To: Re: shafts and props (phil)

Gas engine HP and torque ratings are usually generated at high RPM's, typically 4200 to 4400. Most people never run their gas engines at those RPM's so the effective HP is significantly lower. A 350 HP engine running at 3000 RPM will only be generating about 210 HP.

Diesels on the other hand run near their maximum RPM range and as a result develop much closer to their rated horsepower under normal running conditions. A 300 HP diesel rated at 2900 RPM's will develop 275+ HP at cruise and close to maximum torque.

The torque curve for the diesels allows for much larger props, less slip and more efficiency which is why it is easy to overpower with a diesel and find the stern of the boat lifting and the bow porposing.

You could achieve the same problem if you put big enough gas engines in.

Messages In This Thread

shafts and props
Carl -- Thursday, 10 March 2005, at 10:51 p.m.

Re: shafts and props
Capt Patrick McCrary -- Friday, 11 March 2005, at 1:36 a.m.

Re: shafts and props
phil -- Friday, 11 March 2005, at 7:50 a.m.

Re: shafts and props
craigmac -- Friday, 11 March 2005, at 9:15 a.m.

Re: shafts and props
Rich H -- Friday, 11 March 2005, at 12:05 p.m.

Re: shafts and props
Randy Cootes -- Friday, 11 March 2005, at 12:34 p.m.

Re: shafts and props
carl -- Friday, 11 March 2005, at 12:45 p.m.