Pretty much the first thing that happened when we bought the boat was that the skipper taking us to our new mooring drove us into a low bridge, ripping the mast out of the deck. Since that slightly terrifying introduction to the world of barge ownership we have never got round to repairing it, partly because it wasn't a very good mast, and was bolted into the 8mm steel plate of the deck, rather than the huge, sturdy, formed-of-40mm-steel-plate, massive pillar clearly designed to be the base of a loading crane/mast. One day we will have a new mast built, and it will be lovely, and the mounting for it will be attached to this pillar, but in the meantime, ever since we've owned the boat there have been 8 little 10mm holes in the front deck where the bolts ripped out. We had plugged them with silicone but over time this had perished and dropped out, and having taken out the ceiling in the bathroom we could see the sunshine through the holes (and occasionally the rain too). It was time to plug the holes properly.
We bought some 10mmm diameter steel bolts
and then when Lorna had set up all her welding gear on the deck
i poked the bolts through from below, and held them in place while she spot welded them (i did this with a piece of wood, i like having skin on my fingers! The wood was smoking impressively while she welded).
She then added more welds to get the bolts securely attached to the deck
before i cut off the bolts as close as possible to the deck and ground them down a little
then we repeated the procedure, welding up any holes that were still there and finally grinding everything smooth
From above it's now a nice, smooth, waterproof, seamless piece of metal
and from below you can see the heads of bolts protruding, shortly to be covered up with insulation. Only took us 2 years!