Diesel cruising revs

[msimms]

What revs do you normally run your engines when cruising and what speed does this equate to?

With our twin AD31s 3500 rpm seems to be quite comfortable, about 22 knots but must admit that running at closer to 4000 is more fun. 4000 gives about 28 knots.

Any idea if it's okay to run these Volvo engines just shy of their max rpm for extended periods?

Cheers

Mark

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[DepSol]

about 3-500 revs from top range is ok but I keep my cruising speeds to around 3/3400 rpm on my kad 43

<hr width=100% size=1>Dom

<A target="_blank" HREF=http://www.soltron.co.uk>the website</A>

 

[omega2]

If you can pull specified max revs, run at 200 below all day will do no harm and save you fuel.

<hr width=100% size=1>J HAMER

 

[pissativlypossed]

Volvo advise that the optimum cruising revs on the D6's is 90% of the maximum ie; 3500 x90% = 3150 rpm. At this rpm we are consuming 50 ltrs per hour (per engine) and travelling at 25 knts. the fuel consumption was determined by a laptop during an engine remap so is acurate.

<hr width=100% size=1>"Open Another Bottle"

 

[Boating_Buoys]

Interesting, I've moved from a single petrol to twin diesels recently (and saving a fortune!).

Surely the speed is subject to the size and weight of the boat, but in terms of revs we've currently got a pair of AD31's on a 'borrowed' Sealine S34 and tend to cruise happily at 3,000 very comfortably and economically, whilst maintaining about 20-21 Kts.

When the new boat is delivered; also a Sealine S34 but with KAD 32's what can I expect. ?

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[KevB]

I agree, 200 off max should be ok. Helps if you vary the revs occasionally.

<hr width=100% size=1><A target="_blank" HREF=http://static.photobox.co.uk/public/images/45/99/10714599.s.jpg?ch=97&rr=16:00:39>Nirvana</A>

 

[msimms]

20-21 Knots @ 3000 revs seems a good figure, we're shorter, slimmer and lighter (boat, that is) but would be running around 16-18 knots at those revs. Any idea what props you have? Ours are A7.

Cheers

Mark

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[derekh]

twin kad 32's I cruise at 2800. Wide open they will pull 3900 but I keep having to stop to find my f1 baseball cap. So I seldom use more than 3500 for any length of time.

<hr width=100% size=1>Work ? don't be daft , the suns out.

 

[kimhollamby]

3x/4x series engines are generally rated one hour in twelve flat out only with continuous rating 200rpm less than maximum. So you don't want to bend the throttle right open for anything other than a few sprints and dashes.

You would need to check but I don't think the AD31s are rated as high as 4000rpm...from memory the 150hp version is rated 3900rpm WOT and the 130hp version 3800rpm - sounds like you might be a bit under-propped?

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[msimms]

I can pull over 4100, does under-propped mean I perhaps need larger props?

I have A7s fitted which I believe are the standard fit. I spoke to Steel Developments the other day regarding getting a couple of spare props I have refurbished and was told that if I went to A8s I could expect to lose 500 revs of the top end. Not sure what changes I could expect in the performance with larger props, is it likely that I would still be able to maintain my current maximum speed but at a more relaxed rpm?


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