Modern 35hp marine diesel engine fuel economy ?

alahol2 said:
For the past several years I have been monitoring fuel usage on my Beta 13HP. It works out at a boringly exact 1Ltr/Hr time after time. My usage pattern is the usual tickover on the mooring, short time motoring (upto 20 mins) to clear water, sail, short motor to berth/anchor, tickover while we tie up/anchor. Only very occasionally do we motor for a couple of hours.
To be on the safe side I always plan on 1.5Lt per hour.
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And using my 20 bhph./gallon that's an average of 4.4 bhp. which sounds right for your quoted useage of a 13 bhp. engine. Using the 1 litre per 10 bhp.h. figure would mean that you'd use on average 10 out of your engine's 13 bhp. which would mean lots of max. revs. to compensate for the periods of idling.
Incidentally it's no problem measuring hourly fuel consumption - you don't need lots of steady motoring over big distances, simply read the engine hour meter and record the fuel added. That will give you the average for your typical useage. The difficulty comes if you want to get involved in specific fuel consumption discussions for which you need an estimate of actual power produced by the engine under various conditions.
 
I am going to stick my oar in now! I think the quoted figure of 1 litre per 10 hp used is completely wrong. It is often quoted, my opinion is that it is nearer to 2 litres per 10 hp used.
Show me figures for a semi displacement hull using a 300hp engine at WOT that only uses 30 litres per hour and I will show my arse in front of the town hall clock!
 
Davy_S said:
I am going to stick my oar in now! I think the quoted figure of 1 litre per 10 hp used is completely wrong. It is often quoted, my opinion is that it is nearer to 2 litres per 10 hp used.
Show me figures for a semi displacement hull using a 300hp engine at WOT that only uses 30 litres per hour and I will show my arse in front of the town hall clock!
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we are quoting displacement craft ;)
 
reeac said:
And using my 20 bhph./gallon that's an average of 4.4 bhp. which sounds right for your quoted useage of a 13 bhp. engine. Using the 1 litre per 10 bhp.h. figure would mean that you'd use on average 10 out of your engine's 13 bhp. which would mean lots of max. revs. to compensate for the periods of idling.
Incidentally it's no problem measuring hourly fuel consumption - you don't need lots of steady motoring over big distances, simply read the engine hour meter and record the fuel added. That will give you the average for your typical useage. The difficulty comes if you want to get involved in specific fuel consumption discussions for which you need an estimate of actual power produced by the engine under various conditions.
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4hp is barely over tickover on that engine. I expect if it is properly propped it cruises at around 2500 when the engine is producing just under 10hp. Time and consumption at tickover is so small it is minimal effect on overall consumption.

You have ignored my data taken over a long period - if your figure was correct I would have run out of fuel half way from Sardinia to Majorca, but I still had plenty left when I got there. Nearly the whole distance was under motor. 2400 on my Volvo is producing around 21hp.
 
I have logged all fuel bought, miles covered, engine hours, etc since 2004, during which period the engine has run for just over 1500 hours travelling from Holland to Greece via the Balearics, Corsica, Sardinia, Sicily and others. Engine hours could include some battery charging, although not for the past five years, some motor sailing, transit of Canal du Midi and other abnormal usage. We normally motor at 2000 - 2300 rpm, Yanmar GM30F with maximum revs of 3600 rpm. Fuel consumption over the period 2004 to end 2010 averages 1.24 litres per hour (1732 litres, 1397 hours) Have yet to transcribe the data for the past two seasons but neither was long, about 100 hours, so figures unlikely to change much.

Reading Latestarter's later post, perhaps I should point out that all of this was with a Bruntons Autoprop, 2-blade.
 
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Davy_S said:
Not so! used hp is being quoted, planning, displacement, semi, is irrelevant,
each engine uses so much fuel for hp Used!

I rest my case:)
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Absolutely NOT irrelevant, if we are talking displacement you need to to be looking at a propeller law exponent of between 2.8 and 3. Please remember PROPELLERS MOVE BOATS NOT ENGINES. Beta site is nice and neat showing a propeller law curve which is sadly meaningless as no exponent is quoted!

Also remember to use output to ISO 8665 using sensible 40 Degree test fuel.

If we are are talking older engines please remember they are PROPER Hp not Metric Hp used today i.e 1 Hp = 0.9863197 Metric Hp. Safest to use honest kW.

However in the old days some Briitish Test standards did not include alternator OR water pump and no marine engines include raw water pump parasitic load in advertised power graph.

Is I said at the outset unless you want to become a total spec sheet anorak do no even bother trying.................Apples oranges pears and a few kiwi fruit.
 
Last week went to St Kilda, and lack of wind meant motoring much more than normal. The trip back (Hirta to Barra) was 77 miles, took 14 hours, used 20 litres. Engine Volvo MD2030 (30hp), boat Rival 32, clean bottom. Cruising revs was 1800rpm.
I've always assumed about 1.2 litres per hour at that rpm and 1.5 l/hr at 2000 rpm. Almost never use more than 2000 rpm, as it only changes the angle of the bow/stern, not the speed (by much).

I don't know what HP output that might have meant.
 
Tranona said:
4hp is barely over tickover on that engine. I expect if it is properly propped it cruises at around 2500 when the engine is producing just under 10hp. Time and consumption at tickover is so small it is minimal effect on overall consumption.

You have ignored my data taken over a long period - if your figure was correct I would have run out of fuel half way from Sardinia to Majorca, but I still had plenty left when I got there. Nearly the whole distance was under motor. 2400 on my Volvo is producing around 21hp.
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How do you know that it's producing 32 bhp? If you're reading that off the engine revs./ bhp. graph then that refers to measurements made at full throttle with the engine braked down to the relevant speed and then the power calculated from engine speed and brake torque. In the boat you will be operating at part throttle - sufficient to get the engine to run at the chosen speed when driving the prop.. Under these conditions you'll need far less power and fuel than in the engine test run mentioned above.
 
Tranona said:
4hp is barely over tickover on that engine. I expect if it is properly propped it cruises at around 2500 when the engine is producing just under 10hp. Time and consumption at tickover is so small it is minimal effect on overall consumption.

You have ignored my data taken over a long period - if your figure was correct I would have run out of fuel half way from Sardinia to Majorca, but I still had plenty left when I got there. Nearly the whole distance was under motor. 2400 on my Volvo is producing around 21hp.
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I haven't ignored your rate of fuel consumption data in terms of litres per hour but I question your quoted engine power output. How do you know that it's producing 21 bhp? Have you read that off a manufacturer's graph of bhp.versus revs? Those data are obtained with an engine at full throttle but braked down to a given speed with the bhp. being calculated from speed and brake torque. That's normally a very different situation from the engine installed in a boat and driving a prop. where you will set the throttle to obtain the desired speed although the two situations will coincide at max.engine revs.
 
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