The exhaust muffler shown in the photo appears to be made from stainless steel, and therein lays the problem, particularly if your boat remains idle for longish periods of time. While stainless steel is a lovely material that does an excellent job in most situations, it is not foolproof. It’s Achilles heel is when it contains salt water that lays stagnant for a longish period of time. When that happens the stainless steel will corrode and let you down. Much better in my opinion to use a plastic muffler, just don’t let it get too hot !