One of our boat projects was to replace this helm chair. We have the cushions for it, but they need to be reupholstered, and the stainless steel frame is cracked, so time for a new chair.
Stainless steel is very hard to cut, so I used my Dremel and carbide cut off wheels to cut the frame off the bottom plate. This took about 45 minutes.
The new helm seat has four mounting holes on the bottom. They did not line up with any of the holes on the bottom plate, so I needed to layout and drill new ones. Drilling through stainless is very, very difficult. Drill slowly, and use oil to lubricate and cool the bit. You don't want the stainless to heat up too much because it might become "work hardened" which would make it even more difficult. I drilled 1/16" pilot holes, followed by 5/32", followed by 1/4". I could only drill for a short time before I'd have to stop and resharpen the drill. Luckily, I remember how to do this from some time I spent as a toolmaker apprentice. After an hour and a half of drilling and sharpening, it was done.
Happiness is a new helm chair.