fredcb
New Member
Does any one know whether 1 gallon an hour for a Volvo Penta MD21A is reasonable?
At 6.5 knots it seems thirsty to me.
At 6.5 knots it seems thirsty to me.
Diesel engine fuel consumption
- Thread starter fredcb
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tazzle
Well-Known Member
I was always taught a rule of thumb that for normally aspirated diesels 10hp = 1 ltr/hr at peak torque. If the MD21A is 70hp that would make 7ltr/hr - so doesn't seem so far off. Or am I out on this?
fredcb
New Member
Thats useful, thankk you.
Steve_N
Well-Known Member
There was quite a long thread (which got quite hot under the collar..) on diesel consumption a few weeks back - you might want to search for that.
We have an MD21B which is basically the same engine I think. We can just scrape by on 2.5 l/hr at a gentle 1600 revs, rising to 3+ l/hr at our max of 2200rpm. 2200rpm gives us hull speed so we don't use any more power than that.
If you're not similarly over-engined and use max power/revs then you will burn a lot more fuel than that..
We have an MD21B which is basically the same engine I think. We can just scrape by on 2.5 l/hr at a gentle 1600 revs, rising to 3+ l/hr at our max of 2200rpm. 2200rpm gives us hull speed so we don't use any more power than that.
If you're not similarly over-engined and use max power/revs then you will burn a lot more fuel than that..
No Regrets
Well-Known Member
Our 7.2 metre Rio (Fitted with a 2.5 litre Volvo D3) will achieve 0.7 gallons /hr at Thames speeds.
Nice. very nice.... /forums/images/graemlins/grin.gif
Nice. very nice.... /forums/images/graemlins/grin.gif
A
Anonymous
Guest
I assume you are talking about Imperial gallons? Some of the rules of thumb have, I suspect, come over the pond without modification.
My Yanmar manual shows that at its most efficient (around half power) the fuel consumption is approx. 0.15 litres per horsepower hour. Economy falls very slightly either side of that but the overall efficiency in terms of driving the boat is much more efficient at slower speeds, of course. Mine is a 110hp engine but the figures are comparable for most modern engines, I understand.
Anyway, if you are burning 4.5 litres per hour (1 Imp gallon) then unless your engine is very inefficient for some reason then the shaft horsepower should be about 4.5/0.15 = 30 hp. Does that seem about right? If not, you might be losing some in your gearbox (does that get hot), your stern gland (hot?), your cutlass bearing (noise and judder?) a dirty bottom? high alternator load (80A is 1.5 hp).
If you still can't make sense of this, revisit how you are measuring the consumption.
My Yanmar manual shows that at its most efficient (around half power) the fuel consumption is approx. 0.15 litres per horsepower hour. Economy falls very slightly either side of that but the overall efficiency in terms of driving the boat is much more efficient at slower speeds, of course. Mine is a 110hp engine but the figures are comparable for most modern engines, I understand.
Anyway, if you are burning 4.5 litres per hour (1 Imp gallon) then unless your engine is very inefficient for some reason then the shaft horsepower should be about 4.5/0.15 = 30 hp. Does that seem about right? If not, you might be losing some in your gearbox (does that get hot), your stern gland (hot?), your cutlass bearing (noise and judder?) a dirty bottom? high alternator load (80A is 1.5 hp).
If you still can't make sense of this, revisit how you are measuring the consumption.
G
Guest
Guest
"Anyway, if you are burning 4.5 litres per hour (1 Imp gallon) then unless your engine is very inefficient for some reason then the shaft horsepower should be about 4.5/0.15 = 30 hp. " ....................
Blimey !! My 42HP 4-107 doesn't burn that unless I give it full welly !! Over a 18 hr passage across baltic - I burnt 30 ltrs at 1/3rd throttle .... 4.5kts.
Blimey !! My 42HP 4-107 doesn't burn that unless I give it full welly !! Over a 18 hr passage across baltic - I burnt 30 ltrs at 1/3rd throttle .... 4.5kts.
oldsaltoz
Well-Known Member
Twin 2003's in a 42 foot cat, 7 knots = 1.5 to 1.7 litres per hour per engine depending on sea conditions. port engine uses a tad more than starboard due to larger alternator (80 amp hour).
Avagoodweekend......
Avagoodweekend......
A
Anonymous
Guest
Well, if it was taking 4.5 litres per hour then the shaft hp would have been about 30 hp unless it was smoking terribly? "Full welly" isn't easy to determine on a marine diesel as the 'throttle' connects to a speed governor and the actual power depends on how much fuel is needed to maintain a certain shaft speed rather than a direct indication of power itself.
The fuel used on a passage is so dependent on boat type, hull condition, prop, prop condition, wind and sea that comparisons between even the same type of boat are hard to make.
The fuel used on a passage is so dependent on boat type, hull condition, prop, prop condition, wind and sea that comparisons between even the same type of boat are hard to make.
essexboy
Well-Known Member
How many RPM , at that speed ?
