fuel consumption MD1

It will be pretty much exactly 0.3 litres per kWHr used. That's been the figure for engines from 6HP to 60MW for some years.

But how many HP are you actually using? That's more difficult, but I will calculate for you if you like (I have worked out a fairly involved program to do it). It's a strong function of speed, a lesser function of LWL, wetted area, displacement and hull form (I'd also want to know the prop pitch, diameter, number of blades and gearbox reduction ratio).

The one piece of irrelavent information is the engine make and model btw!
 
The MD1 I had in a heavy long-keeled sailing yacht was fitted with a 4 gallon tank: one day I ran out of fuel, at which point I realised that it had been several years since I'd put any diesel in..... It was only used in general to get in and out of harbour, plus occasional calms.
 
Next thing I need to know is how big my tank is on a mirror offshore.
Thanks for the replies - it seems there is a consensus at 0.6-0.7l/hr
JDC thanks for your reply, I understand that it depends on many factors but was just after an approximate figure at typical cruising revs. Presumably modern engines are more efficient and use less fuel.
 
ghostlymoron said:
Next thing I need to know is how big my tank is on a mirror offshore.
Thanks for the replies - it seems there is a consensus at 0.6-0.7l/hr
JDC thanks for your reply, I understand that it depends on many factors but was just after an approximate figure at typical cruising revs. Presumably modern engines are more efficient and use less fuel.
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ask Dylan Winter of KTL fame
 
ghostlymoron said:
It appears to 10gal (45l)
http://www.keepturningleft.co.uk/wp-content/uploads/Mirror-Offshore-sales-brochure-12.jpg
That's about 70hrs motoring (nearly 3 days).
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I always assume that you get 20bhp.hours per gallon. If you're getting 70 hours from 10 gallons then you're only generating 2.8 bhp whereas I'd predict that you'd need more like 6 bhp. In order to make decent progress. You're also assuming that you can use the whole tank-full which risks sucking in air and maybe sludge.
 
ghostlymoron said:
...I understand that it depends on many factors but was just after an approximate figure at typical cruising revs. Presumably modern engines are more efficient and use less fuel.
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The thing it most depends on is the speed you go: at 1200 rpm I go 4.5 kts and have 1000 miles range, whereas at 2200 rpm I go 7 knots but have less than 500 miles range: the consumption per hour is 4x as much!

Compared to this, the greater efficiency of modern engines is a pretty minor factor (and see http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption, the table shows that one of the best diesel engines ever dates from 1931!)
 
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jdc said:
The thing it most depends on is the speed you go: at 1200 rpm I go 4.5 kts and have 1000 miles range, whereas at 2200 rpm I go 7 knots but have less than 500 miles range: the consumption per hour is 4x as much!

Compared to this, the greater efficiency of modern engines is a pretty minor factor (and see http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption, the table shows that one of the best diesel engines ever dates from 1931!)
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1 ltr per her per Hp used as in post #2
@ 1200 RPM you might only be using 1/2 the Hp ( or less) as at 2200RPM
 
One of the biggest factors in fuel consumption is how clean are the bottom of the boat as well as the prop... as most of us have probably found out.
 
toad said:
When I had a 24ft Snapdragon with a MD1 I used to use between 1/4 and 1/2 litre an hour at cruising speed.
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+1. My Westerly 25 did the same. Take it slow and it just keeps on going with little fuel Motorsailing was the same efficiency but faster
 
macd said:
Probably substantially less than half. It would be nothing to do with the power the engine can produce at 1200rpm, but the power needed to turn the prop at those revs (and a commensurate use of fuel).
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That's quite correct: what I was trying to emphasise to the OP was that there is no such thing as 'typical' cruising revs - 200 rpm can make quite a difference. This paper http://www.awelina.co.uk/hull_drag/fuel_consumption.pdf is slightly out of date as I've since added the effect of waves and extended the analysis to other boats but mine, but it has some I hope interesting graphs showing how the HP used and so consumption varies with boat speed.
 
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I understand well enough that consumption increases with speed/revs/power. Its the same with any vehicle/vessel. Typical cruising speed is not the same for every boat/Sailer but it's likely that similar combinations will travel at similar speed and consumption. It can only be an approx figure and that is all I want and have received.
 
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