Loss of Power in Rough Seas

[Bullish]

Perhaps not a "problem" but a question anyhow. When I am running in a head sea or quarter sea the boat may come off the top of a wave and the Volvo Diesels automatically knock down until she is back in the water and they pick back up to speed. I am not launching the boat and don't run her so hard that the boat pounds. I suspect that the engines are designed to pull back when the props sense they are out of the water...or maybe this happens when the boat senses that the salt water intake is above the water line. Anyhow, the boat holds together fine in these seas and she doesn't hit hard so it is disappointing that I must slow down (off of plane) to avoid this pulling back of the engines. Does this happen to anyone else? Can you tell me what triggers it and is there anyway to change it?

[backman]

Which engines?

My old KAMD 42's would rev right to 4200 when the prop's came out of the water.

The D4's rev perhap 100 RPM's then hold there until the prop's pick up water agaiin at which point they drop back to the proper setting. There is no loss of power however; its a very smooth transition.

[Split Decision]

This is how the commonrail engines work. The computer only gives enough fuel to maintain the set RPM. When the props come out of the water there is no load and the fuel is shut down then starts again when the load comes back. My cummins work the same way. Did you notice that when you climb the back of a wave the RPMs do not change.

Nothing to worry about.

[Bullish]

Thanks guys. To answer your question Backman, they are 2002 KAMD 44's. I didn't think I was doing any harm to the boat but it is still an inconvenience since it takes 5 or 6 seconds to get back to my cruising speed. Once the props are back in the water, the compressors kick back on to help her back up on plane.

Thanks again for your replys.

[backman]

ah; the 44's

EDC controls on top of mechanical compressors. That explains the lag.

W/ the D4 common rails and Tom's Cummins common rails its all computer controlled and you just stay at a steady speed/RPM.

The D4's also have a turbo that kicks in at 1400 RPM and removes that whole KAMD compressor -> turbo interaction which always had a couple second lag.