The US Coast Guard issued a policy letter concerning sea strainers constructed of nonmetallic materials for use on small passenger vessels.
Sea strainers containing nonmetallic components have been installed on small passenger vessels for several decades without incident. However, the regulations were amended to require vital piping systems to be made of a ferrous material on board ”new” small passenger vessels.
Marine inspectors continue to discover nonmetallic sea strainers on ”new” small passenger vessels. These strainers are typically found in raw water cooling systems but may also be installed within other systems. The notion that they represent a potential ”weak link” in a piping system due to the possibility of failure from mechanical or fire damage, which would result in the loss of the affected vital system and potentially result in uncontrollable flooding, simply hasn’t materialized for small passenger vessels. In fact, vessel operators have emphasized that these types of strainers have been successfully used for many years without the occurrence of significant mechanical failures, even when vessels had major fires.
To that end, a search of the MISLE database confirms a lack of historical casualty incidents related to these types of installed strainers. Furthermore, there are benefits to the use of nonmetallic or acrylic sea strainers; they provide improved safety by serving as a sight glass to check for adequate cooling water flow which in turn help prevent main engine overheating and propulsion casualties while underway.
Read the USCG’s policy letter in full: USCG-Policy-Letter-on-nonmetallic-sea-strainers-2016_02