Regarding the original question: I understand you consider putting a 2nd layer of mesh on the inside? Is that with concrete/cement?
If so, I would say: don't do that:
- it would be very difficult or impossible for the 2nd coat/layer to adhere to the hull
- the weight gain on a 54 ft boat, ie 15 mt long, 2 metres high, 10 mm thick, x2 for each side, equals approx 0.6 M2 of cement which will weigh around 1500 kg. And some of the weight will be above the waterline.
If you were to use epoxy with glass fillers/matting etc. That will/could work, although it generally is thought that these two materials have different expansion quotients.
I have put epoxy on of deck
of my ferro boat 15 years ago, not a problem whatsoever, the thickness varied between 4 and 20 mm, thus hiding the unevenness and wavy deck
I have used epoxy on other ferro boasts for repair, and every repair remained 100% attached and intact over the years.
Although I never prepared the concrete with acid prior to epoxy application, it seems a good idea though.
However if there is rust and therefore expansion of the steel
in the hull or deck, NOTHING will work in my opinion.