Gallons per Hour . . .

[wolfenzee]

my engine is rated at 33hp at 3000rpm (max rpm), I found a hp/torque calculator so at 2100rpm, top of the torque curve my engine puts out 22.9hp and pushes the boat at 6.75 knots....not sure about fuel consumption but it is less than 1/2gal/hr

[wolfenzee]

Originally Posted by Panope

If your published torque curve is based on "propeller load" then you have good torque information. If your published torque curve is based on the maximum torque available for each rpm, then we really do not know the torque without more info.

If you believe your torque data to be accurate then you can use this formula.

Horsepower = torque x r.p.m./5252

Steve

max torque at 2100rpm was from Vetus factory specs
2100rpm pushes the boat at hull speed and that is the crusing speed of the engine (about 2/3 max rpm)

[wolfenzee]

knowing the engine used 260 g/KW/h at 2000rpm and the hp at 2100 rpm, I was able to figure the hp at 2100rpm (22.9) and converted that over to KW (17.09) then diesel wieghs 850g/l (7.5lb/gal).....it ends up being a bit less than 1/2 a gal/hr...my head is still spinning

[zeehag]

i find i get 3/4 gph with my brick when bottom is dirty...

[galynd]

I have a Yanmar 3gm30f on a 36 beneteau. At 2000 rpm I used 1/3 gal per hour. At 2800 - 3000 I use 1/2 gal per hour.

[wolfenzee]

That is a higher raving engine than mine, 3000rpm is red lining it, 1000rpm I am doing 4kt, 2000rpm 6.5kt and 2200 stern is squatted down and I am doing 7kt

[bfloyd4445]

Originally Posted by wolfenzee

My engine is rated at 33hp at 3000rpm (max rpm) at 2100rpm, the height of the torque curve. 57.5ft lbs I am doing hull speed....how do you figure hp from torque and rpm?

you cant because they peak at diferent rpm's. You could check with the manufacturer for a set of dyno curves and from that you could calculate hp at any rpm. Best fuel economy is usually at about peak torq rpm. If thats at 2100 for your engine i would say best economy would be at aroung 2000rpm

[wolfenzee]

2000rpm is 6.5 kts, which is what I cruise at (after I discovered the difference between 2200rpm and 2000rpm was only 1/2kt). Though I did run the boat at 2200rpm into 40kt head wind with 15ft+ chop at around 4kt and at almost 2500rpm doing 5kts pulling a 30ft fishing boat. It's nice to have the extra muscle when you need it

[sartorst]

This is what I know about my 33hp 15k lb boat 2 blade prop! 1.6 hours per gallon never changed, I would know before I got to the fuel dock how many gallons I would be putting in,verified over and over by the gurgle in the fuel neck which was handy to stop fuel spills
Note engine rpm 2700 just over the normal (shake rattle and roll) point in diesels
Check it just like you do your car but use time instead of miles

[Hermanns]

Our 75hp Yanmar Diesel runs ~1GPH @ 2000 RPM (6-7kts) and about ~2GPH @ 2500 RPM (8-9kts).

Worth the money in my opinion to take it slower and save the fuel

The sweet spot of efficiency is always best.

[wolfenzee]

the "sweet spot" with my engine is 2000rpm, with my prop that is 6.5kt at .4gph (2200rpm is7kt at 2/3gph...not worth the extra 1/2kt, but extra power can be handy in a pinch)

[David M]

It's not complex at all. Look up the Specific Fuel Consumption for the engine.

[wolfenzee]

Originally Posted by David M

It's not complex at all. Look up the Specific Fuel Consumption for the engine.

It's not hard to find the most efficient rpm...but the most efficiency gph does not necessarily translate into the most efficient mpg...it takes combining the right transmission reduction propeller dia and pitch to match the available torque of the engine.

[Astrid]

If one is really worried about how much fuel is used per hour, why not install a floscan system to monitor fuel usage:

Floscan Instrument Co. Inc.

With exact data in hand, one can then decide what the boat's best economical cruising speed is.

[bfloyd4445]

Originally Posted by Astrid

If one is really worried about how much fuel is used per hour, why not install a floscan system to monitor fuel usage:

Floscan Instrument Co. Inc.

With exact data in hand, one can then decide what the boat's best economical cruising speed is.

pr just not bother and use sail. I mean the world was explored by sail no diesel engines at all