To my knowledge Joshua Slocum didn't have to deal with delamination!
Seriously, it is repairable. Is your hull cored? Is it a full liner that is just loose? Delamination is when the two skins of a cored hull (or more commonly deck as few hulls are cored) separate from each other. Liners on the other hand are usually placed inside the hull with polyester paste holding them in place - both to stiffen the hull and to provide molded attachment points for interior furnishings. If it is not delamination between skins but just a loose liner it's pretty easy to fix. Epoxy is a much better choice than polyester as it gives a much better bond. It is also not as brittle as polyester when cured. Pictures would help. But if you can access the inside of the liner in as many loose places as possible, preferably where it is in cabinets or wherever it won't be seen later. the trick will be to make access holes to pour in epoxy mixed to a mayonnaise consistency. You want it thick enough to not all run to the bilge but thin enough to get in the access holes and fill the gap between the hull and the liner. When a builder installs a liner it isn't attached everywhere - just in a consistent number of places to remain attached and stiffen the structure. If you can access the top of the liner to pour into the gap between it and the hull that would be best - Just put a small (1/4" or so) wedge in all along the join and pour the thickened epoxy in, let it run down a ways and pull the wedges. Use slow hardener to get a longer working time so the epoxy can cover a larger area before it sets. Hope this helps.
ps What is a Mallard?