Volvo MD31A

[Guest]

Anyone know what the operating RPM - max and cruising - are in a typical, say 42 foot, yacht with this engine. Even better any ideas on where the spec. might be found on the web - the Volvo web site doesn't seem to feature older models.

 

[pvb]

Max power at about 3500rpm (nm)

 

[Guest]

Re: Max power at about 3500rpm (nm)

and what would you guess was a reasonable, economical, cruising r.p.m.?

 

[boatone]

Volvo spec for this engine seems to be 62hp @3500rpm.
Assuming (I presume) you have a displacement boat the maximum speed you can expect to achieve is roughly 1.4 X square root of waterline length. eg WL 36 feet max speed around 1.4 X 6 = 8.4 knots. How does this stack up with your actual logged speed at varying revs? Although somewaht higher horse power than my Mercedes OM636 diesel was (42hp) I suspect economic revs are probably similar at around 1500 - 2000. Dont know what that gives you as speed but believe what you will learn from real observation infinitely better than any claimed performance figures. Certainly absolutely no point in thrashing the revs over those needed to achieve hull speed.
HTH

boatone@boatsonthethames.co.uk

 

[johnt]

or more simply : you should expect about 6.5k (cruise)at around 2000/2200 rpm

 

[pvb]

Can\'t you tell??

Every boat seems to have a naturally comfortable cruising revs. You'll surely find that a particular engine speed feels right. I'd guess that it will be somewhere between 2000 and 2500 rpm. The most comfortable speed involves complex combinations of vibration, harmonic frequencies, etc. Ignore considerations of economy - within a few hundred revs either way the economy will be virtually the same.