Join Date: Feb 2010
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Modern sailboats almost always have the head outlet below the static waterline. But, this is more for aesthetic reasons than anything else. It also allows the discharge hose to drain regardless of the heel of the vessel (within reason); which is why greywater outlets are also usually below the static waterline. Ships usually have the outlet well above the waterline, for safety reasons; if a valve and/or hose fails the boat isn't likely to sink.
If I had my druthers, I would locate all outlet thru-hulls above the waterline and put a little "spout" on the outside to keep the hull clean. Just use the holding tank in port and give the thru-hull a rinse with wash-down pump when needed. However, I realize that this scheme might not be practical with all sailboats, particularly smaller ones. (and I'm too lazy to move mine from their manufacturer-installed locations)
The location of the outlet in your pic might as well be below the waterline. It isn't really high enough to protect the boat. However, if you treat it as if it is below the static waterline (i.e., make sure it has a proper valve/seacock, that you keep closed when not in use) it shouldn't be a problem.