Having replaced the CV Midget on A49 with the larger engine, I followed the original Midget exhaust line through the aft cabin using fabricated S/S injection exhaust stubs feeding into high temperature exhaust hoses, hence into a Y junction and thence into a deep Silent Flow silencer and a pipe, carrying, or at least attempting to carry, both exhaust gas and water, passing along the aft cabin sole to a goose neck on the transom outlet.
When the engine was run no water emerged at the transom. No doubt, I assume, because the push of the exhaust was insufficient to carry the water the full distance ,and past the obstacles, to the transom and so it is flooding the system
The cunning of the original twin wall pipe system, which separates water and gas by injecting water into the narrow space between the tube walls, so the water merely cools without losing its velocity, is now apparent.
I am conscious that the low siting of the flat-twin engine design places the exhaust valves close to any retreating exhaust water or advancing sea, if the exhaust outlet were resited closer to the engine to permit the exhaust to carry the cooling water more readily
I would be very grateful for any advice.
Other work goes well; the new keel pins and alloy rudder, afterthe rebuilding of the keel support system, have
allowed me to join the ranks of the swingers. I don’t dare fit the new cabin sole before sorting the bigger engine, given the marginal accesibility.
David
I would not move the exhaust skin fitting if that was what you meant. Wherever you put it apart from the transon it is likely to flood.
I had a wet exhaust system when I had a petrol engine on Calista and it worked well, so I dont think that it is actually the gas flow which is the problem in itself. You mention having a goosneck at the transom end – which of course you should have – but I think that this is just acting as a wier holding water back and allowing it to run back into the engine.
Of course you have not mentioned whether it is filling when the engine is running – I would expect the exhaust flow to take the water with it and not flood the engine while the engine is running. When the engine stops of course the water which will always be upstream of the “wier” will run back towards the engine unless there is a raised “n” bend at the engine end BEFORE the water gets injected it will always run into the engine.
So I think that the solution is to fit a raised injection bend at the engine end, and that may mean 2 injection bends one for each cylender. This must raise the dry exhaust higher than the static waterline before bending over and having water injected into it.
While I am sure you are correct in stating that the dry, water jacketed, exhaust originally fitted kept the gas velocity up, I think that it was more importantly allowing the dry exhaust to be run low down, avoiding the need for a raised bend near the engine. The water was only injected at the transom goose neck.
If you are unable to find room for the raised bends at the engine end you may have to revert to a system copying that originally fitted!
Trevor