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cisco said..Ramona said..cisco said..
Siphon breaker loops and vents are really only relevant when the engine is mostly below the water line but even then not totally necessary.
Anti siphon vents have a habit of salting up and sticking open or shut.
Even if the exhaust outlet is below the water line a water trap fitted just after the mixing elbow should eliminate any back flushing to the engine without the need for high loops just before the exit from the hull.
I'm with you there cisco. I still can't get around the idea that the cylinder head is below the waterline in a Tophat. Siphons are just something else to go wrong. If the cylinder head is above the waterline and the waterlock muffler is below as well I fail to see how water can enter the cylinder head after shut down.
Yes, I think Vetus and others make quite a bit of money out of selling items that are not really needed.
Gee, give me a few beers and a white board and I could easily put together a scenario where an open raw water inlet seacock and a worn raw water pump impeller (which allowed a small amount of bypass) could result in water siphoning into the exhaust/raw water mixing if the attachment point for the mixer was below the level of the water outside the boat (when heeled as well)
I'll be keeping my anti-siphoning device (which incidentally is located just prior to the exhaust/raw water mixer) installed. I also only ever have my raw water inlet open when the engine is running and shut it when the engine is turned off. But to be sure, to be sure Murphy won't get his way, the anti-Siphon is staying.
And my exhaust hose will be staying where it is looped up behind the cockpit seats. The last thing I would ever want is the exhaust hose chock a block full of salt water back to the exhaust water-lock and trying to make it way back to my engine in a rough sea. Why temp fate.
That's the good thing about having your own boat, can can set it up how you want. How my boat is set up makes sense to me and also the previous owners.