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Siphons, anti-siphons & wet exhausts
"JAXAshby" wrote in message ... snip nonsense where jaxie tries to look intelligent, but fails Here comes the potential for trouble. First, when the pump stops there is in fact a siphoning effect (because while the top of the u-shape is above the water line, the outlet is below). Under these conditions (should the exhaust installer fail in his job, AND the boat designer put the engine very low in the boat) there is a need to "break siphon" by installing an anti-siphon valve. Note that this **requires** the anti-siphon valve to be above the waterline under all potential boat heeling positions. I have stated many times that all heel angles and loading condition must be considred. You keep claiming that engines are not installed bleow the waterline, but this is clearly not the case. The engine is below the waterline on almost all sailboats. You should check them out sometime. Second, anti-siphon valves fail due to crud in the water. They always do eventually. The solution for this is regular preventive maintenance. Yes, this is a problem - boats require maintenance. However, this is not too much of a problem with a modern setup. The siphon break can simply be a vent hole with a tube that drains overboard, or into a cockpit drain. As long as water flows out the tube, the siphon break is not clogged. On my boat, the siphon break flow is visible from the helm and is a good way to tell that all is well. Here's the installation manual for the Vetus: http://www.vetus.nl/pdf/03M0405_0499.htm (There is another solution to avoid anti-siphon crudding up but I have never seen it but once.) Not surprising that you've never seen it and don't want to tell us about it. In other words, an engine with its water injection point of its wet exhaust below the water line You mean the majority of sailboats. is in danger of at some point filling the exhaust system with salt water with the engine shut off. A competent surveyor would fail a boat with such an installation. Nonsense. In fact, the 41 foot center cockpit I mentioned was exhaustively surveyed by a gentleman considered the best surveyor of older boats on the East Coast. (I won't mention his name because jaxie would just use it as an excuse to demean his good name.) Actually, any surveyor would fail a boat that doesn't have a siphon break when its needed. If there was no way in hell the water injection point could be moved higher (due to stupidity or deliberate choice by the boat designer) then the insurance company could decline coverage or increase its premiums to cover the greater potential for boat loss. So why is it that the ABYC never mentions this problem? They clearly recognize the issue, since they require a a siphon break in this situation. The are a number of other areas where they say "This should be avoided ..." but they don't in this case. Sooner or later the wet exhaust is going to flood unless the boat owner is deligent about keeping the anti-siphon clean Or installs a proper vent, like the Vetus. AND is damned lucky nothing flukey happens between maintenance events. Like being run down by you? The solution is to mount the water injection outlet **at least** six inches above any potential water line. That would work, but unfortunately most sailboats are designed so that it is not possible. Remember, the ABYC stardard says the issue exists if the exhaust manifold, not just the injection point, is below the water line. Since the manifold is about 8 inches from the prop shaft, its pretty hard to satisfy this without having an extreme down angle and an 8 foot shaft! It is in the installation instruction that come with a water injection elbow. RTFM, guys. RTFM What manual is that, jaxie? Not the Yanmar installation guide - I posted that and it says to use an siphon break. Not the ABYC guidelines - I posted that and it says to use an siphon break. Do you have a secret manual you'd like to share with us? |