It was demonstrably an idiotic thought in the case of my boat''s PO. This is exactly what he had rigged up. The morning I took possesion the engine crankcase was found to be filled to the dipstick hole with water. The reason, later inspection revealed, was that he had done exactly what you propose. Yet every boat is different; it might work with yours. I would strongly suggest you look at a fantastic article on installing wet exhaust systems in sailboats by Jerry Powlas & Dave Gerr, Good Old Boat Magazine, Sept./Oct. 1998 issue. Wet exhausts are a somewhat complex thing to design properly; many things to consider. You can purchase the article on the GOBM web site. It is worth its weight in gold (as are so many articles in that wonderful publication).
A waterlift muffler (I assume this is what you mean when you say "muffler" - note that there are mufflers that simply muffle and do not provide engine protection against backflooding with water.) that will fit your exhaust hose is the Vetus model L40R. (Vetus also sells mufflers that just muffle.)
(no connection with either Vetus or GOBM other than being a satisfied customer)