The wise men are apparently all on tour. But they left me keeping the teapot charged, so whilst they are away the mouse is going to play….
Sounds like good progress is being made on Mary/
Lots of questions in your post (hope the WM don’t come back before I get to the end).
Not sure if you have seen it but excellent advice on Davey’s website here. And they may be a good source of your fastenings.
Some opinions, rather than facts, follow.
Iron rots wood, zinc does not: not strictly true, but the bolt takes up more space as it rusts which can lead to wood damage which promotes more rust which damages more wood which …… The zinc prevents the rust which protects the wood. Stainless bolts are an option but need care to prevent the wood around them getting wet – with no no access to the air they can rust as fast as mild steel (A4 / 316 grade is better than A2 in wet areas.
These need replacing with galvanised or stainless screws, correct? Yes, I would go stainless, well bedded.
But the lower holes I believe the best solution is to line the holes with resin, basically fill them and drill them out again? If the holes are damaged to the point of allowing the new bolts to move around then filling and re-drilling is an option. Not just resin, but resin plus thickener (colloidal silica, micro-balloons, sawdust ….)
You could also increase bolt diameter and drill to that if you are having the fittings re-galvanised when you drill a larger hole.
Goop. This is used to fill the air void and avoid decay? And prevent leaks! The bolt should be a tight sliding fit in the hole. I would bed the fitting and bolts in a good quality butyl rubber bedding sealant. These remain flexible forever. They are available in builders merchants quite cheaply but it is worth paying a bit more for quality stuff like this one. They are messy but clean up easily with white spirit at any time after fitting. Butyl rubber does not prevent the removal of fittings although some force is required. Certainly do use an adhesive sealant like any of the Sikaflexes or CT1 and definitely not anything with silicon. I would not be happy that any grease would provide a lasting seal.
Maybe paint the fittings separately. If you can re-galvanising is far and away the best option for fittings. It is charged by the kg and will have a minimum weight of 50kg or 100kg – way more than you need. But find a fabricator who often sends stuff for galvanising (e.g. trailer manufacturer?) and they might include your pieces. Simple painting of the fittings will not give the protection of galvanising, even with the so-called ‘cold galvanising’ paints. You could possibly get them blasted and epoxy-sprayed / powder coated by a paint shop?
Should I use a tar-paper or similar between the fitting and the hull? Not necessary if using the butyl rubber sealant.
Off to sweep the floor