Cruising Revs

[David of Essex]

I've a single Volvo 260hp D4. 3200rpm is quoted as cruising revs. If running for 4-6 hours would you recommend running at a reduced revs for a limited time or is it OK to run for that length of time at cruise revs

David

 

[hlb]

Whats full revs.

 

[David of Essex]

Think its 3600rpm

 

[hlb]

3400 should be ok then. But if they say 3200, go for that.

 

[Tranona]

Seems a bit high at just under 90% maximum (3600). However, look at the power curves for the continuous rating which will give you a good guide.

 

[Solitaire]

[ QUOTE ]
Whats full revs.

[/ QUOTE ]

3,500

 

[Divemaster1]

[ QUOTE ]
Seems a bit high at just under 90% maximum (3600). However, look at the power curves ..........

[/ QUOTE ]

Looking at the "off shelf" power curves (not for given boat), you'll draw out about 200 hp out of the engine at 3200 RPM (out of 260 available)... This is at about 76% of max load, so should not be excessive..... of course the less you draw out, the less wear and tear ... and as such longer life ... in theory that is...

 

[hlb]

200 revs less than WOT was always the standard cruising speed, much less and you go off the power curve, so use more juice.

 

[Kawasaki]

3200 is ok.
Sea conditions will determine what revs you can cruise at most of the time anyway.

If conditions allow, run at 3200.

At that revs Your vessel will travel along at 16/18 kts?

So that is about 50 miles ish

Good distance for a day for anybody ish.

Or 25 miles out and similar back.
Then its time for cocktails anyway, ish.

Mine is a Large Glenwhatsaname



/forums/images/graemlins/smirk.gif

 

[AdeOlly]

Yep agree with that. I worked out consumption from speed and fuel burn curves a couple of years back, and I get 10% better fuel consumption at the recommended cruise rpm of 3,600 ( about 90% WOT) than at 3,400, and better by about 20% than at 3,200. This obviously may not be the case for other setups though... /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

 

[hlb]

Yep, I've tried going slower. it dont work. WOT less 200 works. Else it's about 6 knots, that works to.

 

[jonboy1]

I have a pair of D4 - 260 hp. According to volvo, peak power/torque is at 2500 rpm. So this should be the ideal cruise setting. At these revs I get 22 - 25 knots.

 

[DAKA]

Theoretically I agree jonboy but in practice it does not work like this.
I agree with others that wot less 10%-15% is most economic for most boats that plane.

I will attempt to explain

I guess you have a light sports boat with twin 260hp.
Your hull will be well out the water at your max torque .
Most boats are no so over powered and it takes a great deal of power just to get them on the plane.
Once on the plane it only takes a few extra revs to gain a lot of speed.

In the old days most skippers said max revs less 200rpm but that was in the days when engines reved to 2000-2500rpm, now engines rev to 3900 and 200 off top may be a little high, I rev to 3950 and cruise @ 3350, I am on the plane @ 2900 but it costs a lot more in fuel to stay at that speed, the extra 450 revs gives an extra 7 knots, thats about 40% extra miles covered every hour.

As to Davids question Volvo that revs to 3600 should be best @ 3200, if out running seastate or trying to make a cil then 3400 for an occasional 150 nm dash shouldnt cause a problem