Boat speed while filling ballast

[z28ke]

I think brokepilot was referring to filling with the engine not running (which I never do because I always select either battery 1 or battery 2 - never both), so coming up this short on the fill makes sense.

[MLA]

The OP's opening statement

I know running above idle helps increase the voltage to the pumps

He may be, but the OP is referring to the difference between idle and above idle, so im keeping with that theme. But just in case, I did include the possible voltage difference between engine off and engine above idle, but I did not do the flow calculation on that scenario though.

I think brokepilot was referring to filling with the engine not running

[gregski]

not sure at what speed the water starts flowing too quickly past the inlets to pump properly.

This isn't a problem. (As long as the intakes are in the water) Actually, moving water has a higher relative pressure which would make the pump more efficient, if anything, but I doubt it'd be in any significant way. The biggest gain is the higher voltage 14V vs. 12V, so long as the engine is turning enough to keep it up, it's all the same (I have to turn >1500rpm to keep the voltage above 13V with 3 pumps running)

[Broke Pilot]

Yea, I misread the op’s post. But, there is a noticeable difference in the pump sound and I’d imagine put out just over idle. At least in my SA. Just at idle I can hear them whine and as soon as you add throttle they jump up too. Is the flow different? Maybe, probly not enough to notice.
Just set your timers for true neutral gear idle and then any amount of water over that is pumped out anyway. No sense in wasting extra gas if you’re sitting.