The main sliding hatch over the companionway receives quite a beating over the years, what with UV, heat, rain and general wear. Eventually the outer ply(s) can start to crack up as the varnish gives up the ghost. The capture piece which fits under the coaming rail to hold the hatch on has been known to rot- after all, rain can run down the hatch sides and run underneath. And I know (from bitter experience) that the rail itself can be broken by a stray shroud as a lowered mast is raised.
The piece of side-to-side coaming which stops the hatch from sliding too far forward or back is fixed by several screws. It may also be held on by previous applications of adhesives or mastic, in which case Persuasion will be required. Once removed, the hatch can be slid off.
A temporary hatch can be fabricated to keep the weather out if the repair work is done outside.
After removing all old varnish, any damage can be filled with a wood filler. If the finish is too unsightly, consider ‘over-plating’ with a sheet of 5mm or 6mm marine ply- Robbins in Bristol can supply very high quality ply (Robbins Elite) at these thicknesses with 5 plys and in 1/4 sheets. This can be epoxied onto the original top surface and nailed (or screwed) down along the top outer edges.
When the coaming piece is reinstalled, make a seal with the small upstanding water stop on the deck and at the ends of the piece; using too much sealant on too many surfaces will make future disassembly very hard.
Finally, a rub of candle wax on the coaming rails will help the hatch to slide easily.
Thanks to Nick Ardley for these pictures from F24 ‘Whimbrel’.