Scrubbing, sanding
Short visit to boatyard tonight, just 3 hours during which I cleaned starboard-side ceiling planks. Procedure as before: first comes removal of oil blobs and old varnish with Bahco blade, followed by orbital sander with 60 and 240 grid paper.
I considered leaving these planks after just scrubbing, to retain patina but the colour became unequal and still too dark. The purpose of this job is not only to refresh them but also to get more light in the cabin hence keeping old stain on otherwise red mahogany contradicts this point.
I took all planks home, to oil them during the week - it is too cold and too wet to do that on the boat.