Bukh DV 24 fuel question

Little Dorrit

Little Dorrit

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Does anyone know roughly what fuel consumption to expect at about 2200 rpm with these engines? I don't have a tachometer but assume at cruising speed about 4.5kts (for a V 27) would be about 2400 rpm with a maximum rpm of 3200. Online research has suggested anywhere between 1.2 litres and 3.3 litres per hour. Any advice practical experience would be good.
 
I don't know but would guess, 2 to 2.5 litres per hour.

Interpolating between figures given in the manual, the DV24 can deliver up to 17hp @ 2,200 revs. At that load you would probably get about 4 lph, but in practice you wouldn't be using anything like that amount of power except in very adverse conditions (and the 'throttle' will only deliver what fuel is required to keep the revs up to the level you set)
 
My V27 has the earlier DV20 and I cruise at about 2,200 rpm on a passage but about 1900/2000 normally. My fuel consumption is around 1.5 to 1.8 litres per hour.

Regards
David MH
 
Well under 2l an hour. You should get a better speed than 4.5 knots at 2400 rpm. You should get 5.5 knots at least and 6.5+ at 3200. So you are either not cruising at 2400 or your prop is wrong.

Diesel fuel consumption is essentially directly proportional to the power you are drawing from the engine and there is little difference between different brands of engines. Your propeller should allow you to reach hull speed at close to maximum rpm and cruise using revs in the range 60-70% of maximum.
 
Tranona said:
Well under 2l an hour. You should get a better speed than 4.5 knots at 2400 rpm. You should get 5.5 knots at least and 6.5+ at 3200. So you are either not cruising at 2400 or your prop is wrong.

Diesel fuel consumption is essentially directly proportional to the power you are drawing from the engine and there is little difference between different brands of engines. Your propeller should allow you to reach hull speed at close to maximum rpm and cruise using revs in the range 60-70% of maximum.
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Unfortunately I think you are right although it's not the prop but the type of prop and set up. As it's a feathering prop I'm not going to get close to theoretical hull speed although I do think it is not set up correctly. I'm not expecting to get 6.5 knots but anything close to it would be good. I have the set up instruction so will dismantle and check when next out of the water. Thanks for the reply.
 
We have a DV20 (1982) which uses between 1.7 and 2l per hour on a deep fin Sadler 32. For a 27 ft boat probably a bit less.

PS it also depends on how much crud is currently attached to the base of the boat.
 
paella said:
Unfortunately I think you are right although it's not the prop but the type of prop and set up. As it's a feathering prop I'm not going to get close to theoretical hull speed although I do think it is not set up correctly. I'm not expecting to get 6.5 knots but anything close to it would be good. I have the set up instruction so will dismantle and check when next out of the water. Thanks for the reply.
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If it a good prop it is irrelevant that it is feathering. It is the diameter and pitch essentially that determine the speed you get. I have had both feathering and folding props and in all cases they have been at least equal to or better than fixed equivalents.

You have enough power from your engine to easily achieve 6.5 knots with your boat if the prop is correct. Ask the maker of the prop to calculate the correct pitch if it has adjustable pitch, and how to set that pitch.
 
Tranona said:
If it a good prop it is irrelevant that it is feathering. It is the diameter and pitch essentially that determine the speed you get. I have had both feathering and folding props and in all cases they have been at least equal to or better than fixed equivalents.

You have enough power from your engine to easily achieve 6.5 knots with your boat if the prop is correct. Ask the maker of the prop to calculate the correct pitch if it has adjustable pitch, and how to set that pitch.
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I think that not all the Jury is not going to agree that folding and feathering are as good as fixed bladed props. The shape of most folding and feathering blades are usually flat (mine are) although I know there are some that are not. But to achieve maximum efficiency when folded or feathered it certainly helps if the blades are flat. Most fixed blades are not flat and I assume are more efficient. I take your general point however that my prop is underperforming and as I have the instructions for fitting including pitch angle I can attempt to remidy.
 
paella said:
I think that not all the Jury is not going to agree that folding and feathering are as good as fixed bladed props. The shape of most folding and feathering blades are usually flat (mine are) although I know there are some that are not. But to achieve maximum efficiency when folded or feathered it certainly helps if the blades are flat. Most fixed blades are not flat and I assume are more efficient. I take your general point however that my prop is underperforming and as I have the instructions for fitting including pitch angle I can attempt to remidy.
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I think your assumptions are not right. Don't know what make prop you have but I would be surprised if it gives inferior performance to a fixed prop if it is sized correctly - which may not be the same size as the appropriate fixed blade. The only caveat here is that some 2 blade folders, particularly the cheap ones and sold as "racing" may well not perform as well. However, from your description you don't have one of those.
 
After 7 - 8 hours of good motoring 2000+ rpm cruising 6 knots I usually use 2 gallons Bukh 24. Dip the tank after each run well impressed with fuel consumption. I do have a big prop mind.
 
I find that I get about 2L/h from the Bukh 24 in my Sadler 29, but the biggest variable for me is when I dive in and clean the prop, turns it back into a prop instead of a whisk.
 
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