Although not fitted with a Volvo or a 54, Cream puff is fitted with a Vetus Waterlock muffler. Even if you do not have the Vetus model, the setup for the water-lock is probably very similar. The muffler is fitted with a drain screw. Undoing this screw while underway would absolutely eliminated any chance of water back-flowing into the engine. If you opt to do this, it might be advisable to attach a hose pointed toward the bilge. And, of course, do not run the engine with the water-lock drain open.
So, for those of you not wanting to run the engine at all while underway on long passages, this is an alternate option.
With best regards,
Sailing Vessel - Cream Puff - SM2K - #275
Currently cruising - Vista Mar, Panama