QSC propping to engine load

[Luke Nelson]

Hi Guys, I am after some input on engine load to propping. I have just swapped out a pair of 3208’s to qsc 540’s. I think I may be close but everyone wants more speed if they can have it.

The props were calculated on the 490 hp curve to keep within the shaft limits for survey( I am using marinex hs22 2.25). I can post the full numbers but at 2400rpm I get 19.5 knots @ 120 LPH and 52% load. At 2600 I get 22 knots and 74%.
The engine hits the limit on the govenor no issues. On one engine I can get 14 knots at 100/100 I figure if I derate the engine( I am avoiding this unless I am forced to do it for survey) to what the prop is I would be around 80% at full load.

The boat is a charter/ work boat 26T metric fully loaded but we never need full power at that load, max likely around 22-23 T ish. The props are new 5 blade Veem Star 25 x 25.5. The way I see it I am not loading the engines and they will
have no issues and last for every.

Thanks Luke

Topic

[Luke Nelson]

Thanks Tony,
It makes sense when you say it like that. The sea water sides are on my list to strip and clean.

thanks Luke

[Tony Athens]

Luke,

Only ONE way to really determine where you are, and IT’s not load %…………..You need to graph your fuel burn against the Cummins fuel curve applicable to your engine……….Also, remember this if nothing else.. You cannot under prop engines like this, you can only over prop them. If you are happy with your vessel speed at RPM”s 300+ off your WOT rpm in your circumstances, then to me you are good to go..

Maybe Corey will finish up the graphs he is working on and post one for your engine that you can fill out. Then graphically “see” what you are doing at various RPM’s..

As to how long they last, on SWAC engines with very complex mixed metal component on the seawater side, you need to take care of these per our protocol, specially the aftercooler.. Your unit could easily be 8-9 yrs old now, so it’s need to gone thru ON THE BENCH..

Tony

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