So I’m starting on the biggest and hardest of the old through-hulls. All others have been removed. I decided to cut this one in eight pieces instead of four so that I can break off each part with a hammer and chisel as with the smaller through-hulls. This one is in very good shape, though. Nevertheless I will feel better when it has been replaced. Why?
1. It has no backing plate!
2. It has no seacock flange!
3. It has no valve attached!
It is at the waterline, and it is the biggest hole in the entire hull, therefore it is important to make sure nothing goes wrong here!
I will know that EVERYTHING that passes through the hull (where it can end up under the water when the yacht is heeling) is NEW and made in the ABSOLUTELY BEST WAY POSSIBLE.
You could say that I don’t need to destroy this nice through-hull to fix points 1 and 3. The thing is that even if I skip point 2, the easiest way to remove the through-hull in order to install a backing plate is to cut it up into pieces. Unscrewing through-hulls can be close to impossible, crawling around in thight spaces trying to make huge spanners fit around the nuts and not get caught on things inside the yacht. And then the through-hull can still just rotate along with the torque, if you can get it to move at all against all resistance that sikaflex and other things cause.
I also found when working on it that the hose from the engine exhaust has rusted (the steel inside the rubber walls) and the rubber walls are getting brittle and dry. So it will be a good opportunity to replace everything.

This picture shows what I have done with the tiger saw – cutting inside as well as outside. But due to the length of the blade and the thickness of the saw I can not cut parallell to the hull, and therefore quite a few mm of material is left uncut along the outer sides. I will get back to these grooves with my fein saw.

After curring with the fein saw and hacking away with hammer and screwdriver and a chisel I could remove the pieces one by one. Much harder work than for the other through-hulls. Unfortunately I made some small scratches (<1mm deep) in the gelcoat. One job generates the next task….
First I thought that the inner ring was a wooden or fibre glass backing plate oddly set on the outside of the hull. But it was in fact just more bronze material that would take time to cut. All in all this is a high-quality through-hull that I am replacing. It did not show signs of deterioration.