kweetoo, the mess is what ime trying to avoid should I ever need to use one, I've seen the destruction with powder on engines and wiring looms , also when they have fallen from bad mountings or left loose in truck cabs, when we tilt the cab they near destroy the interior with the clean up job being almost impossible. so it looks like dry water will be a better choice, just need to get down to the boat and see what sizes to fit and where to put them.
was thinking 3 ltr in saloon, and 1ltr in each of the berths and deck locker.