Fuel Consumption

[Sootydog]

I'm beginning  to doubt my fuel calculations. I don't want to let the tank get too low and I'm struggling to find someone willing to supply me with diesel. Can any one confirm the fuel consumption ( litres per hour) of a Volvo d1-30 running at between 1400 to 2000 rpm on average, fitted to a 39 cruiser.  I make it between 1.3 and 1.5 litres per hour but I'm now wondering if I have got this right.

Many thanks in advance.

[Symphony]

That range of hourly consumption is correct for a D1 30 - although you are running at below optimum revs which should be 2200+/-200rpm which will give you a cruising speed in the range 5-5.5 knots. Check that you can achieve a minimum of 3000 rpm at full power with w clean bottom and in flat water. If you are achieving over 5 knots at under 2000 rpm this suggests overpropping.

The D1 30 is rather small for for a 39 at over 8 tonnes and I would expect to use more rpm to achieve a decent cruising speed

[Sootydog]

Thanks for the reply Symphony. I will check on the speed per revs later this week but I hardly ever feel the need to run at 2000 rpm.  If it helps, flat out ( to clean some soot) is about 7.5 knots from memory  It's an ex charter boat so I wonder if it has been deliberately over propped to reduce the revs or would this mean unnecessary strain on the engine

[Symphony]

It may well be overpropped - the test is can you get above 3000rpm (out of the full 3200). To pass the Volvo commissioning test it must achieve this. My D1 30 is propped to give 3100 in a much lighter B33). 7.5 knots is a bit less than should be achievable in a 39.

It is a myth that reducing revs by overpropping reduces strain on the engine - in fact rather the opposite as taken to extremes it overloads the engine and causes premature wear. Engines should run continuously at around 70% maximum revs under load - that is about 2200rpm for this engine, and from time to time given short runs at full power.

[Sootydog]

Symphony,
Checked out the revs today. I think the boat may be ever so slightly over propped but I think nothing to worry about ( 5.5 ish kts @ 2000 rpm )