355 Aft Cabin milage

T

timjet

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Mar 7, 2010
RO Number
32060
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Does anyone have some good info on the expected fuel mileage of a 355 ACMY.
My diesel powered 355 gets up on plane at about 1800 rpm and does about 13 kts. At 2000 rpm it gets almost 20 kts.
The fuel charts indicate better mileage at 1800 rpm, but from my experience, just adding 200 rpm and getting almost 7 kts more would be far better.

Anybody know??
 
what fuel charts are you looking at?? I dont know if any boat that does well just on plane.
 
From the Cummins fuel charts:

FUEL CONSUMPTION - PROP CURVE
rpm l/hr gal/hr
2800 65.8 17.4
2600 50.6 13.4
2400 40.1 10.6
2200 31.6 8.4
2000 25.4 6.7
1800 19.7 5.2
1600 14.9 3.9
1400 10.7 2.8
1200 7.8 2.1
1000 5.5 1.5
800 3.7 1.0
600 2.6 0.7

It seems that fuel mileage is better at 2000 rpm burning 13.4 gal/hr at 20 kts which comes out to 1.5 MPG compared to 13 kts at 1800 rpm and 10.4 gal/hr which computes to 1.25 MPG.

That would seem to agree with what pdecat said.

Anybody have some actual fuel burn data??

Tim
 
I dont see from those curves how you got the idea that 1800 was the best rpm?
You are using the correct curve and your thinking that more speed per rpm change is on a right track. Try collecting some more data and look for the point where the speed increase per rpm increase slows down. that would be the highest point where going faster uses more fuel than it's worth. Keep in mind that the fuel increase over than prop curve is very non linear so fuel is increasing much more rapidly as rpm increases and best cruise will probably be lower.
You can also plot fuel uses from the curve against speed for better info however the curve is at best an approximation and works only in bow down running and well on plane.
Do you have pyrometers?? My guess would be between 22 and 2400 RPM.
 
Its been a while since Ive run a diesel boat, but 200 RPMS equals out to 7mph once on plane?

Sounds high...
 
I got some real world data. You're right pdecat, 1800 is a terrible RPM, I got only 8.5 kts.
It does look like 2200 is best, I got 18 kts and at 2000 I got 14.5 kts.
Thanks guys
 
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