What's a realistic estimate for the fuel burn rate for a VolvoPenta D2-40F (or similar 40hp engine) pushing a 37' late-model, 15,000 lb sailboat at a steady rate of 2300 rpm, through reasonably calm, saltwater bays?
Our D2-40 uses a little under one gallon/hour at 2200-2400 rpm. That’s in line with Volvo’s published figures, although those need to be taken with a grain of salt because they are for a specific loading, The engine maxs out at about 2 gallons/hour at full power.
Over the 10 years we have had our boat with a D2-40F I've been trackingfuel usage and with hand on heart I can say 1.9 litres per hour.
Based on number of hours run and litres of fuel put back into the tank at the end of the year. So this will be a good average of usage including close quarter manoeuvring, cruising at 1800rpm, reverse setting the anchor at 1500rpm and occasionally higher bursts but never more than 2500rpm.
What's a realistic estimate for the fuel burn rate for a Volvo Penta D2-40F (or similar 40hp engine) pushing a 37' late-model, 15,000 lb sailboat at a steady rate of 2300 rpm, through reasonably calm, saltwater bays?
The numbers in my notebook show about 1/2 gallon (2 litres) per hour. But some of the published estimates I'm seeing show 4x that amount (2 gal/hr).
Somebody's wrong big-time! I'm OK if it's me. (Learning is always good.) Anyone care to share what they think a typical figure might be?
I'd say 1/2 gallon an hour minimum and maybe 5/8 gal an hour. The 44 ft boat in my avatar had a 51 HP engine and my log showed 5/8 gallon an hour average for the life of my ownership.
My cat with two 3GM30 yanmars (26hp?) burned <1/2 gallon each engine.
The 80 hp Mercedes in my quite heavy 47 foot boat burned 1 gal + an hour.
__________________ "I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard
If you’re running at 1800 rpm that’s only about 5HP, your engine is too big
Seriously, no need for hand on heart, that’s exactly what Volvo says it should use at that speed.
1800rpm gives us 6kts cruising speed so why burn any more fuel than we need to? We could have had the 28hp engine but I'd rather run a larger engine at lower revs and be comfortable in the knowledge I have power to spare than run an smaller engine hard and have nothing left over.
Over the 10 years we have had our boat with a D2-40F I've been tracking fuel usage and with hand on heart I can say 1.9 litres per hour.
Based on number of hours run and litres of fuel put back into the tank at the end of the year. So this will be a good average of usage including close quarter manoeuvring, cruising at 1800rpm, reverse setting the anchor at 1500rpm and occasionally higher bursts but never more than 2500rpm.
came pretty close to that (total overall including on idle during anchor-up & -down, warm up, motoring at 1500 in offshore calms never more than 1,5l/h, mostly less)
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1800rpm gives us 6kts cruising speed so why burn any more fuel than we need to? We could have had the 28hp engine but I'd rather run a larger engine at lower revs and be comfortable in the knowledge I have power to spare than run an smaller engine hard and have nothing left over.
second that!
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...not all who wander are lost!
I'll take a larger engine worked less hard any day. That's why I dont like Yanmar engines, they are light weight simply because they are over rated at high rpm to express more HP.
__________________ "I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard
I'll take a larger engine worked less hard any day. That's why I dont like Yanmar engines, they are light weight simply because they are over rated at high rpm to express more HP.
Volvo is no better. The D2-40 is rated at 39.6hp at the crankshaft (38hp at the propeller shaft) but they don't list the rpm for that. The stated range is 2800-3200rpm, so one might assume the test is at 3200rpm. The underlying engine is the Perkins 404D-15 (which is actually a variant of the Shibauru S774L-D), and is rated at 35.5hp at 3000rpm (crankshaft) in their brochure. Shibauru shows that these are net power ratings; continuous power is closer to 32hp@3000rpm. So our 40hp engine is actually 20% less in continuous usage. I suppose that is only a modest bit of puffery.
The amount of fuel a Diesel engine uses is directly proportional to the load on the engine. The engine is designed such that the throttle determines RPM, and fuel is fed to achieve that. A good approximation for Diesel engines is 0.054 gallons per hour per horsepower. So, to find consumption for your engine, you need to find the horsepower EXPENDED at a given speed. You need two curves for horsepower vs RPM, one for the engine and one for the selected propeller driving your boat. The engine curve goes up fairly quickly, peaking at about 3200 RPM or so. The curve for the propeller driving your boat curves the other way, primarily because the water resistance to your hull rises as the square of speed (and much faster as you reach “hull speed”. Boats are generally designed so that the propeller size and pitch are selected so that the two curves meet at the maximum horsepower the engine can deliver. Otherwise, the engine will be overloaded at wide open throttle, or Will not be loaded enough to ever get to its potential. At lower speeds than wide open, the propeller will not be taking as much power as the engine can give. For your engine, assuming the propeller is taking say 38 HP at 3200 RPM, at 1800 RPM it is probably only taking About 10 HP. This would then mean your fuel consumption at 1800 RPM is on the order of 0.5 gal/hr. My boat is similar in size to yours, with a similar size engine (40 HP), but probably takes a bit more HP for a given speed, as my displacement is 18,000 lb. I get an average of 0.6 gal/hr at 1800 rpm (5.7 kt) and about 1.0 gal/hr at 2000 RPM (6.2 kt) both in fairly smooth water. Over the whole range of activities (in/out of harbors, anchoring, moving the boat when the wind doesn’t suffice) I measure 0.55 gal/hr based on fuel required to fill the tank divided by engine hours averaged over a season. This has been consistent over 16 years.
I did a web search and found this very nice article by Dave Gerr at www.gerrmarine.com>Articles>EnginePowerCurves. He found the same number for gal/hr/HP that I mentioned. More rigorous and a better explanation than I gave!
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