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Consumption BMC Sealord 6 cyl, 100Hp, 1983


Anderl
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Can anyone help me with the consumption of my engine?
I have a steel sailboat 12m long. 4m wide with a long keel. The boat is 17 tons.
My BMC Sealord 6 cylinder with 100 HP needs about 10 litres per hour at low speed through the water, which seems a lot to me.
I noticed this because I am temporarily using a 20 litre can as a tank.
Is this normal or what can I check or do about it?
The engine runs very smoothly, is dry and starts on the second.
Thank you for your help,
Andreas

 

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Where does any fuel return pipe run to?

 

Its not unknown for people to run on a temporary tank and get a high fuel consumption because much of the fuel is being returned to the original tank.

 

It will also depend upon what speed "low speed" actually is and the hull design speed but assuming we are talking say 4 knots or less then extrapolating from known consumption inland where the water is not free to pass down the hull I would suggest about 2 to 3 litres an hour wont be far out.

 

The engine size is not that relevant to sub plaining speed consumption but actual speed through the water will be. I think consumption is likely to increase by the  square of the boat speed.

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The engine does seem large: I used to sail quite a lot with a friend on his 38’ (thus similar size), steel ketch, 6’ draught with a full length keel. Admittedly he had a pathological dislike of ever using the engine unless forced to by safety concerns, but it was only a small two cylinder Volvo. What size exactly I’d have to ask him, but it wasn’t big, I can all too clearly remember grinding in the valves on one head while moored fore and aft at anchor off the Isles of Scilly. The head wasn’t big and if the engine was much more than 1.5 litre I’d be surprised.

Checking the fuel return line, and whether or not it has an appropriate propeller fitted could be one way to go?

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37 minutes ago, Tony Brooks said:

Where does any fuel return pipe run to?

 

Its not unknown for people to run on a temporary tank and get a high fuel consumption because much of the fuel is being returned to the original tank.

 

It will also depend upon what speed "low speed" actually is and the hull design speed but assuming we are talking say 4 knots or less then extrapolating from known consumption inland where the water is not free to pass down the hull I would suggest about 2 to 3 litres an hour wont be far out.

 

The engine size is not that relevant to sub plaining speed consumption but actual speed through the water will be. I think consumption is likely to increase by the  square of the boat speed.

You are spot on there Tony. I learned this the hard way in the Bay of Biscay when delivering a 32 ft yacht and couldn't understand why the temporary 20 ltr tank I was using was emptying quite rapidly and the main fuel tank on the boat was filling quite rapidly.  Most of the fuel supplied to the injectors is used for cooling them and then returned to the main tank. When using a temporary tank the injector return pipe must also be fed back to this same tank.

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Thank you for the quick responses.
Tony, I think you are absolutely right. The bad thing is that it was not unknown to me with the return line but I have not thought of it. I was probably mentally already with the crane. Sorry!

But what is certain is that I drove through a calm and had no power or tide. (Mediterranean Sea)
But I noticed that the throttle can not be adjusted well in the minimum range. The 3 blade propeller makes a normal and undamaged impression compared to other ships in the size. Since it is a used exchange engine is even older than my ship (engine year 83, ship 89) and before a 30 hp engine has pushed, I do not think that this size was absolutely necessary but it was probably available and gives security;-)

Well now she stands on land but I can, since I had pumped the tanks empty, let's see what flowed back.

 

 

Best regards from Munich,
Andreas

 

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Many thanks for your feedback.

 

I suspect you took the trouble to feed your reply through Google to get it into English so thanks for that but in order to make suggestions about the low throttle adjustment we ned to better understand what you mean (must be difficult trying to technical stuff in a different  language).  Unless you changed the propeller I suspect the problems relate to propeller size. You have all but tripled  (3 times) the available power.

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