I would do around 6 of these jobs a year, this gp is around 20 years old.It had got some staining of the deck by moisture from being left outside in winter.
First i removed all the fittings.
I pressure washed the boat inside and out to remove any salt, then enclosed it in a polythene tent with an industrial dehumidifier. 24 hrs a day for a week. This sucked all the water out from below the varnish, getting rid of the dark marks. The alternative would have been to strip varnish locally from the stained areas and sand,revarnish…problem with this is every area thus sanded would come up a much darker colour,owing to the sun having bleached the wood over the years.
There were some ares where the varnish had lifted from the wood and they had to be stripped back and revarnished,but they were quite small,and should fade back down in a while.
i recoated all the bare wood with 6 coats of 2k varnish,sanded down the interior and deck,transom etc and first masked off the deck and sprayed 2 coats of 2k varnish,then masked the interior and sprayed the deck and transom,2 coats 2k varnish also.
Next job was to sand down and repaint the floor of the boat with grey paint including coarse grit.