Originally Posted by sanibel sailor
I have a water lift muffler. Water can still be forced past it under certain circumstances.
I take a loop of the flexible exhaust hose as high as possible inside the locker the exhaust runs through and down to the transom exit. I made a copper flapper (with a plastic hinge on a short piece of PVC tube) angled 45* on the outside so gravity closes it. Similar to the flappers you see on truck vertical exhausts.
I have found that seacocks, cast fittings and valves create unnecessary back pressure restrictions to the exhaust flow. Especially it's a restriction when some people extend them by sticking a piece of plastic tubing inside the cast fitting. Then a 1,1/2" dia can become 1" dia or less and we can all do the math on the crossectional area reduction. Some forget that the cooling
water is also occupying the pipe and its crossectional area along with the gasses.
One thing diesels really need is a free flowing exhaust.
My transom fitting is fabricated from 1,1/2" dia SS thin gauge tubing (18 / 20 g) and a circular flat plate for a flange with a matching transom angle. It's 17 years old with no signs of corrosion
I've extended it with a short length of exhaust tubing on the outside with the flapper on the end. That is flexible and goes under the boarding platform and won't damage a dinghy
One reason for the flapper is to prevent damp air blowing through the engine in the unlikely event of water in the water lock evaporating when not in use as now.
That's my way if it helps.