Cummins QSB 380 Operating Loads

[searaydeal]

Cummins MerCruiser doesn't normally post operating loads, but they do post "cruise rpm" for their engines. See the link below:
http://www.cmdmarine.com/engines/ratings.html

Your engines are considered HO ratings, so you would run 300 rpm below the WOT rating.

 

[osd9]

From the link above.....

Rated Speed (rpm)
Cruise Speed (reduction from rated speed, rpm)

Less than 2800 rpm
200 rpm

.......I guess 90-95% of throttle is recommended for cruise by Cummins.....I stand corrected...

 

[Four Suns]

From the link above.....

Rated Speed (rpm)
Cruise Speed (reduction from rated speed, rpm)

Less than 2800 rpm
200 rpm

.......I guess 90-95% of throttle is recommended for cruise by Cummins.....I stand corrected...

They make it pretty clear, at least in my Cummins Captain's Briefing material as well as the manuals that "cruise" is 80% load... So... however the hell the electronic load meter calculates that is beyond me... but I know for a fact that the 80% number gives different RPMs depending on how the boat is loaded. If I have full fuel, full water, a jet ski on the rear, 2000 pounds of cokes and beer, 1000 pounds of shoes, 500 pounds of dog food and am on the ocean side, I can tell you that 80% load is down around 1950 RPMs and not 2100... So one has to be aware of that...

I'm not sure how Cummins sets the upper throttle limit. I doubt it's the "screaming about to destruct top end" but I don't really know... I do know when I show 80% load at 1950 RPMs, I can still get to 2300 RPMs so I'm not really sure that 2300 WOT for a Cummins QSM-11 is set the same as CAT does it...

 

[elreyos]

I don't have my engine manuals in front of me. I could be wrong, but I believe I calculated recommendations to be something like 8mins out of every hour of operation at WOT as acceptable. Running a 600hp 8L diesel at Wot is scary. Even though the engines sound like they love it thats a lot of reciprocating mass being tossed around.

 

[ImpulseIII]

By the way wot on my 40' is 3000 rpm's and the cummins mechanic said I should hit that plus another 1000 rpm's or something is wrong. I also had my props computer ballanced and checked and it made a big difference in how smooth the boat runs. Also at 2500 rpm's my speed is 22.5 to 23.5 mph depending on total fuel, water and people on board.

Are you saying that 3000 is WOT but you should be able to add 1000 to that? That would mean your engines can spin up to 4000 RPM. Is that right?

 

[tobnpr]

I think he meant 100, not 1000...

 

[Rocket]

So... however the hell the electronic load meter calculates that is beyond me... but I know for a fact that the 80% number gives different RPMs depending on how the boat is loaded. ...

That is a good point - How do they calculate load?