This is the main seawater strainer, which feeds the engine and the sea chest . The top of the strainer is above the waterline and can be cleaned out without shutting off the thru-hull.
Initially I was going feed the engine cooling water from the sea chest but after hearing of various issues (thanks Patrick) I chickened out and took a "T" off the main intake directly to the engine. A valve after the "T will allow me to isolate the sea chest in the event of a leak in any of its hoses, therefore permitting the engine to remain operational.
