I decided to take the rudder apart and fix it; I'd done something similar with the anchor well cover many years ago. When I started cutting it open it was clear the entire thing was waterlogged, with the internal foam disintegrating. There was also as I recall a split in the fibreglass on one side (I'm writing this in 2022). I decided to remove the entirety of the old foam and replace it, so I cut away a chunk of the starboard side and pulled out the foam in pieces, either by hand or using an auger drill to get into crevices.
I repaired the broken GRP from the inside, and replaced the repaired bottom edge section, adding glass on both inside and outside to strengthen it. Then I glued some pieces of new closed-cell foam in place, and closed up the remaining panels. Then I drilled holes and injected two-part polyurethane foam, letting it expand into the remaining spaces. That involved mixing the foam and quickly putting it in a large syringe body, putting the plunger back in, and squirting it in the holes before it had a chance to expand. The syringe was of course wrecked after this, but it managed to work for many consecutive injections. After that I faired everything over with a sander, and applied coats of Interprotect epoxy waterproofing (as I'd used on the rest of the hull, after a history of "osmosis").
As I recall, a temporary wooden support while gluing up a split in the port side.
There's a long piece of bronze acting as a stiffener astern of the propeller opening.
Closed-cell foam in place, with some two-part already in the lower portion. As I recall, I made GRP sheets to overlap on the inside, glued and held in place with aluminium pop-rivets, so that when the cut panels were replaced it would end up mostly flat, before chamfering and filling the join on the outside. The idea was to do this only in the middle of the rudder. The edges which are under higher stress were built up with multiple layers of glass from the inside in the normal way.
Andrew Daviel, 2018/address>