what expected fuel consumption

My Volvo 50 hp 4 cyclinder 2 litre diesel uses 2.5 lit /hr at 2k revs, delivering into an S leg with fixed 3 blade prop. Above 2k revs the consumption rises exponentially - I have seen 11 lit/hr at the max 3k revs in literature, but never proven it!

PWG
 
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Any idea how much fuel per hour with a 54hp Yanmar on a 43' boat?

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I think it all depends on hull shape, weight etc but this might help as we used the Yanmar figures which are 2.5 ltr/hour for estimation and were miles out.
Although we are a Catamaran and have twin 54hp Yanmars on the trip from Cape Town all our motoring was done on one engine at 2000 to 2200 rpm. We weigh around 15t fully loaded and are 46ft long but obviously 2 narrow hulls with mini keels rather than 1 slightly more beamy. We averaged between 3.5 and 4.0 ltr/hr depending on currents and waves. One engine will push us along at 6 knots in a flat sea.
 
Based on a specific fuel consumption of 170gm per hp-hr your consumption will be, when delivering the following powers...

10 hp 1.5 litres per hour
20 hp 3.1 litres per hour
30 hp 4.6 litres per hour
40 hp 6.0 litres per hour
50 hp 7.7 litres per hour

Works out very well for me up to 100 hp. I tend to cruise with about 25 hp (just under 25% of my engine's max output and comfortably in the operating range) and I am a 42' Nauticat.
 
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Based on a specific fuel consumption of 170gm per hp-hr your consumption will be, when delivering the following powers...

10 hp 1.5 litres per hour
20 hp 3.1 litres per hour
30 hp 4.6 litres per hour
40 hp 6.0 litres per hour
50 hp 7.7 litres per hour

Works out very well for me up to 100 hp. I tend to cruise with about 25 hp (just under 25% of my engine's max output and comfortably in the operating range) and I am a 42' Nauticat.

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I found that fuel consumption for steaming into a strong head wind could almost double fuel consumtion for the same revs in calm weather. On my old Victory 40 with 75HP Perkins, it used around a gallon an hour at 7 knots flat sea, and around 2 GPH into a F7. The extra consumption (Solent to Camaret) caught me with my pants down, as we ran out of fuel in one tank just as we were entering harbour - a quick switch to tank 2, bleed, and 3 minutes later running!
 
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Based on a specific fuel consumption of 170gm per hp-hr your consumption will be, when delivering the following powers...

10 hp 1.5 litres per hour
20 hp 3.1 litres per hour
30 hp 4.6 litres per hour
40 hp 6.0 litres per hour
50 hp 7.7 litres per hour



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I cannot understand your figures. Even if one accepts your consumption of 170 grammes per Hp/Hr (I would have thought that 270-280 would be more like it), drawing 20 hp from an engine over a period of 1 hour would consume 20 x 170 = 3400 grammes. If it were using water, this would be 3.4 litres - but diesel is lighter than water... no?
 
Yes, I did make a mistake, thanks for pointing it out. I multiplied by the specific gravity when I should have divided. So 170g per hp-hr is 170g / 0.90 = 188.9 cl per hp-hr. So the 10 hp figure should increase to 1.9 litres per hour, and the others pro-rata of course.

hp litres per hour
10 1.9
20 3.8
30 5.7
40 7.6
50 9.4

The figure of 170 gm per horsepower-hour is the standard Yanmar figure published in their engine tables. You will find comparable figures in Wiki and elsewhere. That is shaft output, of course, which is also what you engine is rated at. A 54hp engine has a max rated shaft output of 54 hp. What that means in terms of power delivered (as thrust) to the vessel is an entirely different matter, of course.

Do note that your terminology is wrong. It is not hp/hr it is hp-hr. A very different thing, though it looks as though you used the number as hp-hr.

Sorry for the arithmetic mistake - I have been working with the wrong figures for a couple of years and not noticed -- 20% or so is not a big deal when it comes to estimates in the real world but the table does give us an indication of usage and range.

I shall try to modify my earlier post if the system will let me edit it. Thanks again /forums/images/graemlins/smile.gif
 
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I found that fuel consumption for steaming into a strong head wind could almost double fuel consumption for the same revs in calm weather.

[/ QUOTE ]Yes, that's normal and it's because the engine is run by a governor, not a throttle. Your throttle lever is more of a 'set propellor revolutions' control than a throttle. So if you are bashing into a sea, have a fouled prop, or unusual hull resistance due to dirt or being overladen, you will find your fuel consumption will rise hugely -- i.e. the engine needs to develop more power to keep the prop running at those revs -- and with an engine in good condition (i.e. little tendency to smoke or overheat) you might not even notice until your fuel starts to go at an alarming rate. I have often thought of fitting a fuel flow meter for that reason alone....last May I motored from Almerimar to Mar Menor (no wind /forums/images/graemlins/frown.gif ) and was getting through fuel very fast. When I dived in Mar Menor I found a rope round the prop. Had I known earlier, I could have anchored in several places to clear it but my engine does not smoke or overheat, so I didn't notice.
 
No problem, Lemain; I was not criticising you.

I meant it as 'grammes per horsepower hour' when what I had in mind was 'grammes per kiloWatt hour' which, in the case of my Lombardini LDW903M, is given as 272 grammes at 2400 rpm and 5.5 kgm on the MN curve.

What is important for people to realise is that the rate at which fuel is consumed by a diesel engine depends on the work that it is actually doing, and not on the engine revs or the speed of the boat through the water. Accurate, meaningful, measurements of this can only be achieved through the use of a dynamometer. Failure to be aware of this factor can easily lead to nasty surprises, usually when least desired.
 
Yes, but depending on the sort of passages you make, it is worth keeping in mind your endurance at low power as well. In extremis, you might want to ride a storm using the engine to keep bow to windward when you'd only need 20 hp or less. It is worth having a note of your range and endurance at full power (flight), fast rated cruise, slow cruise and maximum endurance. That's where those tables come into their own. It's not likely to be an issue in the Solent but it might be crossing Biscay, for example. I could easily motor non-stop from Southampton to Gibraltar without fuelling at maximum endurance.
 
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It's not likely to be an issue in the Solent but it might be crossing Biscay, for example. I could easily motor non-stop from Southampton to Gibraltar without fuelling at maximum endurance.

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Good point, Lemain. One would, however, be very optimistic - not to say foolhardy, IMHO - to expect a similar performance when doing the same trip back from Gibraltar to Southampton because the prevailing wind and water conditions are likely to be significantly different (adverse).

On a general note, I always advise, where possible, to fit a day-tank and to keep an accurate fuel log that includes conditions. This helps to build a reasonably accurate picture of what consumption to expect, given a particular scenario. Unfortunately, some people feel that the day-tank option is an unnecessary luxury or, at best, a nuisance.
 
We have a lot to learn - we are in the nw of cumbria so our local area is the Irish sea north of the IoM. Hopefully this year we will get to Wales and Ireland on the shake down cruise but it is handy to know some braod figures to go on.
Don't want to give myself and swmbo any home made issues through being a numpty and not asking questions - hope the forum doesn't mind too much
 
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Don't want to give myself and swmbo any home made issues through being a numpty and not asking questions - hope the forum doesn't mind too much

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But that is precisely is why the forum exists! Why should anyone mind?

None of us know all that there is to know about everything - although some of us do give that impression. /forums/images/graemlins/wink.gif Only a fool would not ask about things of which he is unsure. The fact that you ask indicates that you take the safety of your boat, of yourself and of your crew very seriously.

There is a wealth of experience in this forum and one would be silly not to tap into it. Of course, you will sometimes get conflicting advice; we all have our pet solutions that have worked for us - but not necessarily so for others. As time goes by one learns to adapt the advice / opinions given to suit the situation at hand or to disregard it if it does not apply.

Enjoy your new boat and may you always have fair winds!
 
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