delaminated 3 skin- repair suggestions

My boat is built of 3 diagonals, apparently the epoxy in the 60's wasn't the amazing goop it is today and there are areas on the hull that are definitely hollow sounding when tapped. I know the difference between stringers, furniture and other solid areas btw. The cure that comes to mind is to place a decent ply plank between the stringers and screw from the outside in and squeeze it up. Lots of screws! Any improvements on this idea?

 

If it is delaminated, the immediate main concern is water intrusion. You should open and dry all those areas. The other concern is structural. Triple diagonal is a monocoque construction. If the laminate fails, the boat will sink.

 

Fifteen years ago I had to do a big repair to a 1960s Bill Garden sloop named RAMPAGE in San Francisco. She was 60 foot ocean racer of 4 diagonal lam construction over bulkheads with stringers that were too far apart. Had many lam fractures in outer 3 lams due to heavy sailing and was going to be scrapped. I used a router, one layer at a time, to surgically cut back the problem areas and lam in new material. Then I put a ply doubler between stringers in a couple of places on the inside where needed and shored it in place while glue kicked, no fasteners. Boat is sailing today and looks new.

 

thanks, I was also thinking of drilling through the stringers from the inside- say 150 centres and fastening with about 1000 bronze screws from the outside. That said the boat is watertight, there is no weeping on the hard suggesting the hull is waterproof. Its just there are hollow patches. Perhaps it was like that from the get go, but still Id like to improve it if I can as I hate nagging doubts.

 

You'd be better to not fasten with metal, motorbike - but you could drill numbers of holes to touch the outside layer, not through it, and inject epoxy glue and then apply pressure, a lot of pressure, from both sides simultaneously while the epoxy cures.