AD31P fuel consumption

chillee

chillee

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Anyone have a single AD31P in around a 25ft craft. Interested to know what you find your most efficient speed and revs is and what sort of fuel consumption you get.

Just acquired a 25ft Hardy Seawings. New to such a craft and a diesel engine, coming from a 20ft bowrider with a 4.3 mercruiser.
Trying to figure out where the sweet spot is.
Thanks
 
I have a similar size boat with the same engine, on average I get around 4.5 to 5.5mpg cruising around 20knots at 3500rpm which seems to give the best economy. When cruising (which is most of my boating activity) I always set the throttle to 3500rpm subject to sea conditions as the boat feels right at that speed etc.
 
thanks Scubadoo - helps a lot. This is about what I was anticipating, but by my calculations over a trip from Poole to Itchen river and Itchen to Yarmouth I used 92l (Was full when left Poole) and filled up in Yarmouth. So I make that approx 3.2mpg.
I cruised at 3400 rpm. 19 kts on the wheel - considerably less on the GPS
clean bottom
against tide most of the time
Have to say at 3600 rpm she seems to sit up on the water a bit better, and so might be more efficient like that, but coming from a petrol engine before I felt that might be pushing it a bit on the revs for cruising. Is it normal to cruise at a higher percentage of revs on a diesel ?
 
I am also cruise in the same area Solent etc, there could be many factors regarding mpg e.g. boat weight, hull design, props, sea conditions etc.

If 3600rpm feels better then I would try that and see how you get on, it won't harm the engine. The AD31 max rpm is 4100 and the volvo penta manual states "volvo penta recommends a cruising speed approximately 200rpm lower than the maximum rpm at wide open throttle". So basically I wouldn't want to cruise for long periods anything over 3800rpm. Also what props do you have, that will affect performance / speed to plane / top speed, mine has A6. Hope that helps.

Also I should say there are occasions where I have recorded mpg to be around 3.5mpg.
 
Thanks. Not sure on the props. Will have to wait till I have to lift her in the winter. But she runs between 3900 and 4100 at WOT. 25 to 26kts. So whatever they are sounds like they are probably the right ones.
 
Hi there.
Not sure if it’s of any use and may even bore you...but my friend had a similar weighted 2t cruisers 224 with an AD31 150hp turbo diesel. At the same time I had a similar weighted Sealine 218 with 4.3 petrol 205hp. The Sealine would cruise at much lower rpm at 3000rpm and hardly breaking sweat at around 22/23mph gps. The cruisers would be at around 3700rpm and screaming at the same speed....I’m pretty certain using more fuel, but of course the fuel price of red diesel was so much less. Added to this...with the hoods up...you literally couldn’t talk to each other with the noise of it.
I’d imagine with the same engine and your hardy (no doubt a proper and serious boat and much admired...by me at least), it has a semi displacement hull and will perhaps never plane in the sense that the cruisers model above would...hence perhaps struggling all the more ??
Just my thoughts.
 
Thanks Qbhoy some good insight much appreciated.
The Seawings range from Hardy were in fact full planing hulls. Will see if i can figure out how to upload a picture.
 
Our last boat, a Mustang 2800 sports cruiser was fitted with two AD31,s and she would use around 40lph
 
Thanks. Assume that's for the 2 engines. Not each ?

Ran at 3500rpm today. Feels like she is sitting on the water much better. So will try a few runs like that before topping up the fuel and checking again.
 
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