I've been following this post with interest because, as Jerry said earlier, the E32-3 has the same setup (none of which I understood until reading this post).
I agree with Cory's thought that,
“I am still a little confused though why they "vented" the antisiphon line to a fitting that is sometimes below the waterline when the boats in motion. But at rest it would obviously do its job….”
Most of these systems are new to me but it seems like this anti-siphon loop would have to be viewed in two different ways, depending on whether the engine is running or not running.
With the engine running: (it seems…..)
- (1) there is no need for the anti-siphon function of the loop. The engine is putting out enough exhaust gas pressure to force both air and water up a 1.5” (or greater) exhaust pipe. The danger of water “entering” the exhaust pipe (let alone, progressing further, via siphoning, into the engine) with the engine running should be a non-issue.
- (2) the danger of exhaust fumes entering the anti-siphon line at the tee (and thus, venting at the line's exit point) seems remote. A steady stream of water should be flowing through the raw water line (that the anti-siphon line tees into), on it’s way to the mixing elbow. If a steady stream of water is not running through the line, you have bigger problems and a pending overheat, and you won’t have the exhaust fumes for long….
- (3) the possibility of water entering the anti-siphon line at the “tee” seems pretty likely. This would occur if there is corrosion or blockage past where the raw water line hits the injection elbow. A flow restriction at the injection elbow might force water into the anti-siphon loop. This possibility may be one of the reasons why Ericson plumbed the anti-siphon vent back to the exhaust pipe at the thru-hull: it may have to vent air, water, or both.
With the engine stopped: (it seems…..)
- (4) now there IS a need for an exhaust-line anti-siphon loop (if your engine is below the waterline). The head-scratcher here is that with the engine stopped, say when sailed and heeling, it's possible that both the exhaust line and the anti-siphon vent (which share a thru-hull) are submerged……and you have no anti-siphon protection in precisely the situation when you need it.
- (5) obviously, there is no danger of exhaust entering, or engine raw-water leaving, the anti-siphon loop with the engine not running.
So………..If the above are true, then ideally, the anti-siphon loop should be vented to the atmosphere in a location that is
A) above the waterline when sailing (#4 above), and
B) suitable for the drainage of both air and water (#3 above)
This gives me the thought that high up on the transom might be the ideal place for an anti-siphon vent. On my boat, the fuel tank vent is on the port-side upper transom.
Maybe the starboard side would be the ideal place to vent the exhaust anti-siphon loop.