So rather than the traditional foam and vinyl, has anyone tried 4mm marine ply and routing a tongue/groove effect pattern into it? If so, how did you attach it? No more nails?
My boat has 3mm ply linings in most areas. The builder put them in. They are nailed to battens fixed with some kind of adhesive to the grp hull. This adhesive has failed in some places and I have re-secured the loose battens using epoxy. That was before I found out about CT1, which I would probably use in future.
The plywood is simply painted with Dulux kitchen/bathroom emulsion. This lasts a long time and is easily maintained.
Cierzo has (as standard), something like 6mm ply (but poss 8mm*) headlining, routed to give a planked effect, maybe 3mm deep*. Fastened by countersunk screws, variously to ribs or bonded-on pads. Very strong, tough and still looking good after 25 years. The white surface is either spray-painted or lacquered, easy to clean.
* I'd be happy to measure it but won't be aboard until next week.
Our boat is largely lined with ply panels (some painted, some varnished), trimmed with teak battens, and very nice it looks, too.
It works largely because although actually built in GRP, the coachroof is designed square-ish to look like a traditional wooden one, so there are few of the areas of double curvature you would typically find in a more 'modern' looking boat. Double curvature would probably make ply lining rather complicated.
The panels on our boat are fixed in place with teak strips - mouldings which are screwed up into the inner layer of the cored deck. There are also some horizontal fixings (where the cabin sides are not cored), but I'm not clear whather these just screw into the ply, not the coachroof itself (these particular panels are also held in place by the window frames).
One way of fixing screws to the inside of a GRP coachroof would be to glue on 'Big-Foot' or similar nuts.
Even with our simple shaped coachroof, shaping and fitting these mouldings would be a task demanding a lot of patience, time and skill. Our boat was fitted out by a woodwork enthusiast. I think it would have been prohibitively expensive to have it done professionally. (The yard finished sisters of our boat have foam backed vinyl linings.)
The actual headlining on my Hunter is moulded, in good condition and doesn't need faffing with. But the vinyl on the cabin sides etc is all totally kaput. I've replaced some of it bust most is still to go... and given that I'm painting most of the interior to brighten/modernise it I found myself starting to wonder if actually some ply might not be an effective alternative.... so easy to work with... easy to maintain... and I think done right and in moderation tongue and groove effect on a boat can look great... Really easy way of doing sole boards too perhaps. If you aren't bothered about external quality then "marine" ply is pretty cheap too...
Of course whether it would look out of place on an 80s styled production cruiser might be a different question.
We did it last winter. Going to break it up a bit with some vinyl and have teak battens along the edges. Thought about routing and black sikaflexing, but looks good varnished. Attached battens with gorilla glue, a full year now without any signs of lifting. Started in the forepeak as I think in the main cabin it might be a little overwhelming.