Cutwater 30 cruising engine RPM

[Robertsn12]

Hello all - I don't know if this has been discussed elsewhere on the site, but we have a new Cutwater 30 S and beyond rule of thumb of max RPM less 10% for new high speed deisels such as the Volvo D6 435 on our boat, wondering what others cruise at (speed, fuel burn, engine RPM). Thanks for your feedback,

 

[davidr]

We have a CB30. Often our cruise speed is dictated by our cruise partners...our boat is faster. But, if we are just motoring along, we use 2000 rpm...that gives about 9 knots ar 5.5 Gph. She seems very happy at 2500 rpm, 14 knots at about 9 gph.

 

[Robertsn12]

Thanks David. We are anticipating a longer cruise with some days of 60 miles or more. When we are just loafing along, we run at about 1250 rpm (6 knots and 1 gph), but when we are in a hurry we run up to 3200 rpm, 16 gph at around 22 -24 knots. Just wondering if anyone else runs for extended periods at that engine rpm on the Volvo d6 435? The folks that did the engine cert after we took delivery told us we should try to run the engine at high speed for at least 20 minutes at the end of each day to keep it running clean noting that these new high speed deisels don't like to run slow.

 

[davidr]

If I recall, at the Roche Harbor rendezvous last September, the Volvo factory guys said it was fine to run at 90% WOT all day. It was a great session. Had not realized that the d6 was the first Volvo engine designed from the start to be a marine application.

 

[Shano]

We tend to run our CW30S at 75% load which depending on wind and current is usually around 2800 RPM and 19 to 21 knots and depending again on the current, wind, and seastate about 1.25 nm/gal to 1.35 nm/gal (at 20 knots 16 gph to 14.8 gph). We will run our boat for hours at 75 to 80% and if we are in a rush go to 90% load. Frequently the seastate dictates what load/speed we run at. We will frequently cruise at displacement speed (about 7 knots) during lunch or sightseeing and get up to 4.5 nm/gal. I will adjust the rpm to the efficiency so that I can to get the max nm/gal. If we are cruisng at low loads for long then we will usually run up to higher loads (75 to 80%) for a while. Your Volvo panel can be set to show all sorts of indicators like % load and the Garmin MFD can be set so that you can see nm/gal or mpg and vessel range whichever you prefer. Of course I like it the best when we are running with the current downriver on an ebb and then I can get up to 1.6 nm/gal at 28 to 30 knots!
Enjoy your new boat!

 

[Robertsn12]

Thanks all

 

[Connerkip]

Running between 8 knots and 12 knots is just pushing water. I avaoid these speeds for sure.

 

[bill46]

We have a R-31CB.
Agree with Connerkip 8-12 is just a waste of fuel.

We either cruise 7-8 mph trawler speed at 1800 rpm 3 mpg or fast 14-16 mph at 3000 rpm 1.5 mpg.
Adding Bennett fins to trim tabs, repainting bottom and new prop gained a mph or two and maybe 10% better fuel economy at high speed.
The boat wants to get more efficient the faster it goes, but I do not want to go over 90% RPM.
I wonder how it would run with D6 435hp like cutwater has?