David,
Having gone through this, here is my experience.
I bought a pipe wrench to remove the valves and thru-hull nuts. You can borrow the wrench if you like. I haven't used it since. I got all the valves off the thru-hulls except under the sink. There was no way that I could get the pipe under the sink without completely dismantling the boat cabinetry. When I applied wrench to engine cooling valve, it snapped right off along with the nut. I was able to knock the thru-hull out. It turned out to be the easiest one to remove.
So, of the five thru-hulls, I had one completely removed, one with the valve stuck on it, and three with nuts. The nuts came off two of them easily (sorry I don't recall which ones.) The nut on the third wasn't going to move not matter how hard I beat on it with that wrench. I believe it was one of the toilet ones.
I used the wood blocking with nut and bolt method to pull the two thru-hulls out of the hull where the nuts were removed. The old thru-hulls were installed with some pretty tough adhesive. There was quite a bit of gel coat cracking and splintering, around the hole, during the removal process. It was not a fun moment. Almost cracked a tooth from gritting them so hard.
This left the thru-hull/nut/valve under the sink and one other thru-hull/nut. It was about this time that the grinder method was bought up. I was able to beg/borrow an angle grinder from a friend. The theory was to cut the mushroom head off the outside and knock the thru-hull inside the boat. So I first tackled the sink thru-hull/nut/valve combo. Grinding was not as bad as I had imagined. It was done fairly quickly. I started to wish I had done this with all of them. However, the thru-hull/valve proved impervious to theory. No matter how hard I strained, grunted, cursed, and hammered, it would not come out. Since the valve was still stuck on it, I couldn't use the block/nut/bolt method on either side. So biting the bullet, I pulled my arms out of joint (not really
, and VERY CAREFULLY inserted the angle grinder under the sink. I was able to cut the valve off without severing any digits. I did not find that there was enough room under the sink to use the block/bolt/nut method on the inside. So I used the grinder on the nut. It was not fun and I ended up cutting into the fiber glass a small bit due to not keeping the grinder disk level with the hull under the sink (do mostly to not being able to see inside, very well, with my arms in the way). I was able to use the block/bolt/nut to remove the remaining piece from the outside. However, I had to make a trip to the hardware store to find a washer that was just slightly smaller than the outside diameter of the thru-hull, in order to pull it out.
The last one was easier. I ground of the outside head, then used the block/bolt/nut on the inside to remove it.
Lessons Learned: No matter what method you use, if the thru-hull don't want to come out, it will be a pain in the privates. If I was going to do it again, I think I would start with the grind method. If you are lucky, the adhesive will be weak enough that you can pull (or poke) the whole mess, thru-hull/nut/valve, from inside. Then do valve removal, on the ones that won't budge, and use block/bolt/nut to extract from inside, if feasible. Otherwise, try to remove the nut and pull outside.
Chris
V-2933 Renee
Chesapeake Bay, USA
