repower 23 cc inboard

riprunner · #26 01-28-2011, 10:40 AM

Quote:

Diesel hp and gas hp ratings are not measured the same, diesel hp is rated at the shaft, thus, the hp rating isnt the same bro...

Huh?... HP is HP. HP is the same Diesel or Gas.

Horsepower = Engine Torque (Foot Lbs) x Engine Speed (RPM) then divide by 5252. That is how HP is measured. The TORQUE (ablility to rotate mass)of an engine is a huge component of the POWER of the engine.

Gas engines make their high HP DUE TO RPM.
Diesel engines make there HP DUE TO TORQUE.

Hence, a 180 HP Diesel provides the same Performance as an approx 250 HP gas engine does at low RPM aka Taking off and getting on a plane, but may not have the same great top end MPH performance.

Thus am I correct that the higher torque of the diesel enables it to turn a higher pitch prop, thus greater travel distance/revolution, thus higher speed for the diesel for the same RPM?

Yes, you are correct. But with, say, only 2800-3000 rpms from a diesel, (depending on the motor) the top speed is affected.

That is true that top speed could be affected, but who cares. Let's face it, these boats are not even close to being fast especially in today's standards. The most important thing for an inboard Seacraft is a solid economic cruise speed. Nothing will do this better than a diesel.

I would love to be able to cruise at 24-25 knots, but with a 350 gas motor, it will never happen on my boat.