J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Anti siphon valuse

Has anybody installed an anti-siphon value in the engine raw water intake to stop the need to close the engine seacock to keep from losing prime while under sail?

You shouldn't need to close the valve. If you loose prime, you probably have an air leak somewhere between the seacock and the suction to the raw water pump. I had a problem that turned out to be an air leak with the gasket at the top of the raw water strainer. I replaced the gasket and haven't had a problem since. Also make sure you have a good air tight seal for each of the hose fittings. You can have a water tight connection, but still have an air leak.

Try an experiment - run ~ 3 foot hose clamped directly on the raw water pump suction to a bucket of water sitting in front of the engine. The raw water pump should take a suction and self prime when the engine is started. If that works, you definitely have an air leak in your setup. If not, you probably need to change out the impeller, and potentially the back plate on the raw water pump.

The hose in the bucket method is how I winterize my engine, through the seawater strainer after cleaning it out. I can tell right away when I haven't sealed the strainer cover gasket properly.

First I would just undo the water strainer top, clean the gasket and then screw it back on. They key is to make sure the nut that is used for the hinge and the wing nut put equal pressure on the base. Often the leak is from OVER tightening the wing nut so the top is not flush. So try re-seat it and screw it in finger tight. This will probably fix your issue.

This just sounds like a raw water pump issue to me as I believe all of the components including the pump are below the water line.