Re: Thru Hull Exhaust
samm, I'm not gonna jump on the bandwagon, and say noise, because I'm sure you've figured that out, and it is a subjective thing, some people like it, some don't. I've done it on 2 different boats in the past, one had a 305/228hp, and the other had a 350/260hp. The advantages, I did notice a cooler running engine, never over (140-160*), and more oil pressure, plus I always could see if I was pumping water! and a minor boost in HP, but you're not gonna be able to sneak up on anybody,,,lol,,,and think twice before idling down a canal in the wee small hrs of the morning,,, or otherwise, be considerate. The 305 I didn't bother putting mufflers on, but the 350 definitely needed mufflers, I put on these all rubber mufflers, with slight baffling in them , don't remember the name? but they were great, they mellowed it down like glasspaks. Wait, I think they were Salisbury mufflers?
All I did was take off the hoses on the risers, and marked the transom inside by running a coupla straight lines from the top, bottom, and sides, of the riser elbows, to the transom, (checking, & rechecking the measurements) till I was sure it was good, then took a 1/4" bit, and drilled a hole through the transom at the exact center inside, then took a hole saw (of the proper size to fit your tips into,) about 3", and drilled it thru from the outside, slipped my tips in using 4200 as a sealer, then screwed them down, and went back inside to measure how long a piece of 3" exhaust hose I needed to fill the gap, and using some engine oil, put the hoses on, One important issues is, you must use 2 hose clamps at each end, making it redundant, for what I heard was Coast Guard regulations! The rubber exhaust hose will help quiet it down some.
On some installations, you may need to put 3" high, or higher spacers, under the riser (elbow) before you begin anything,,, I had to do this on one of my boats, don't remember which one?
