420/44 DB Owners Club

My Rpm’s stayed the same.

 

What speed are you running before and after sorry my wot maybe 2730 rpm’s at 30.3 SOG

 

2730 is high, if memory is correct 32
Her is the chart from Seaboard marine https://www.sbmar.com/articles/proper-propping-specs-of-the-cummins-marine-qsc-8-3-500-hp-engine/

 

This is the correct rpm range for the Cummins QSC
See chart https://www.sbmar.com/articles/proper-propping-specs-of-the-cummins-marine-qsc-8-3-500-hp-engine/

 

So maybe they need some cup?

 

One more thing, when I had my props redone from 24x27 M-cup props to 24x27 Light cup props I went from planing cruise of 2275-2280rpm and now I need to hit 2300rpm before it planes.
Here are a few screen shots of before and after the prop work.
The 2289rpm is with M-cup props at 25.7mph and the 2307rpm is with the new Light cup props and 23.1mph
Note: I do MPH not knots

 

My other set of props the boat was faster.
Do you run here at 2300 rpm on a all day cruise?

 

Yes hours at a time.

 

If WOT is 2665rpm with old props then you are in the optimum range for longevity of you QSC motors, 2730 is too high although it is less load on the motors which is good too but your loss of speed is more
https://www.sbmar.com/articles/proper-propping-specs-of-the-cummins-marine-qsc-8-3-500-hp-engine/

 

I just talked to a prop guy and he said I need alittle cup. If I can get her on the hard I am going to change my props out , back to my original ones and have my new ones cupped alittle.

 

If you carry full water and full fuel along with all the other little spares etc the factory 24x27 M-cup is just a bit to much on mine and went to the light cupping. Info should be stamped on your props.

 

The props I took off r m cup. Not sure what I put on it, but this was on the box

 

I wonder if those have no cupping since nothing is stated on the box

 

If you look at the charts from sea board marine Tony Athens talks about the more critical part of proper propping.
Fuel burn at different rpms

 

That’s what I am thinking, no cup. I gonna swap them back out with my originals that got redone.

 

I seem to trip the GFI in the forward head whenever I switch between shore or gen power. Hopping it’s just a bad gfi outlet. Anything else I should check?

 

GFCI receptacles do not last forever. The surge, as small as it is when you flip the switch could be enough to trip it.

Super easy to change out the GFCI as a test. Do not forget to turn off the breaker!!!

Let us know if you find a cause.

 

Does anyone know if there any rules or cautions with the keys in the ‘ON’ position?

Just wondering if they have a time limit if left in ON when engines not running.

 

I wonder the same thing. I think it just powers up the helm items.

Curious, what does your accessory DC switch control on your STBD side?

Cheers!

 

Not sure they matter other than the fact you can accidentally start from helm. Not likely but it could happen…heck I’ve accidentally laid on the horn. My rule is at anchor I leave the keys on in case I need to get out of dodge in a hurry. At the dock they are off.