Exhaust Pipe Seals

You have to loosen the two hose clamps on the inside first before the flange will come off. Sometimes you can have someone pull on the flange gently to create a gap so that you can apply the caulk without loosing the clamps.

Is the caulk applied to the inside between a flange and the inside of the hull or on the outside under the chrome flange? And yep, the chrome trim pieces seem thin and they do have a lip.

What type of caulk is best? Hardening? Non-hardening?

Jim,
Hhmmm. Never seen the 3/16" nylon ring before. I wonder if it was originally cut too large as if a Chrysler or Holman Moody engine was going in which used the larger pipes. Mine were a rather tight fit and caulked. As for caulk, 3M 5200 is the standard and found at just about any marine store. It never gets completely hard and is good for underwater use. The stainless or copper thru-hull pipe was glassed in on the inside of the hull on many of the older ones. CC cut grooves in the pipe to help the glass adhere to it. I just recently removed them from the old orange 67 Nautique when I replaced the 2-1/4" pipes with 3" thru-hulls for use with a larger engine. So, you may be able to take a block of wood and bang it from the outside. But if you have no plans or need to remove the pipe and only want to remove the hose, then you probably will have to remove the tank. Not a big deal. Since I was replacing the thru-hull fitting, I smacked on it with your suggested method to no avail whatsoever. It just dug a round hole in the wood. I ended up cutting them off as flush as possible with a Sawzall, and then using the hole saw to cut around them. Pain. They were glassed in very well. I did a similar replacement on my 69 Mustang and they weren't glassed in. Only had to break or tear the caulk joint. If you're replacing the exhaust hose anyway, it may be worth it to go with the 3" stainless pipe and maybe not need the 3/16" spacer, and if you think it sounded good before, the bigger pipes will only add to it. Also, if you have an industrial pipe company close by, you can actually buy the 2-7/8" thin wall copper pipe for less money than the rubber exhaust hose, esp if you're talking about reinforced hose. This is for the straight section under the floor. CC used this method in many boats, as did Century and Chris Craft.          

Reid/Jim,

Great post and one of the item's on my list when I get home.

Good Luck,

Another new term. What is bedding compound?

Bedding compound is sold by Interlux paints #214. It is used to install(bed) cleats, hardware & thru-hull fittings. 3M 5200 is an excellent product but remember "5200 is forever. If you need to remove fitting in the future 5200 is tough to remove. Bedding those screws come from my experience repairing boats when some one installs a fitting, ei pitot tubes, transducers, etc... and uses a fastner that is too long. The fastner then leaks water around the threads into the hull. Also bedding screws seal water from getting into wood backing causing rot problems.