Inside or Outside repair patch on mast
We have a question about whether to install an internal or external patch when repairing galvanic corrosion on the mast at gooseneck and spreaders. We’ve read the threads on this issue and notice that photos of mast repairs show aluminum patches welded on the outside of the mast. At KKMI here in Richmond, CA (Swan certified boatyard) the metal worker has suggested the option of an internal plate inside the mast (inserted inside through control lines through top and bottom of mast, cemented and bolted in place). The advantage of the inside plate is that the gooseneck is able to attach in its original position. Option B is to attach the support plate on the outside of the mast at the gooseneck. This would involve changing the shape of the gooseneck fitting to fit the shape of the new surface. Is there an opinion about whether it is better for the plate to be inside our outside of the mast?
Note: The corrosion is not extreme: the plate is only recommended because our plans are for long distance ocean cruising.

Apologies for not signing the above post.
Kim and Mark, Swan 41/059

Dear Kim and Mark
My preference would be to put the plate on the inside, will be less visible than an outside one. Assume the plate will not extend to the forward edge, where the mast cables form an obstacle.
Structurally an inside reinforcement needs to be slightly thicker than the mast wall, at least 0.8 mm (1/32") more would be fine here.
There is only one yacht named Anthea in the member list - easily verified.
Kind regards
Lars

Dear Lars,
Thank you so much for your prompt and helpful reply. The yard has proposed using a section from an old Swan 41 or 44 mast. That section may not be thicker than our mast, so we'll communicate with the yard the importance of ensuring that the aluminum patch is at least .8mm thicker than our mast wall.
With much appreciation,
Kim and Mark, Swan 41/059