vinylester resin repair below waterline?

[sailorjoey]

Good ol' Don Casey does not recommend using poly or vinylester resins for repairs below waterline? My whole hull is vinylester resin so why would he recommend against it? Of course I will be using gel coat to protect the laminate so it is not exposed to water. Also he recommends throwing some fiberglass cloth in between several layers of mat. Why is this necessary? I understand for the finish layer you want to put cloth over it but I don't get why you need to alternate mat to cloth.

[CharlieJ]

Mat in and of itself, contributes little strength bi-directionally. Builds bulk. Cloth in between ties all those random fibers together. Often recommended is two layers mat, a layer cloth, more mat, as needed.

[Godot]

Not being the expert Mr. Casey is, I think that Vinylester would really be fine. It is stronger than polyester, but weaker than epoxy. It is probably in the middle regards to water absorption as well, so theoretically it would be more prone to blisters than epoxy, but less than polyester. I, personally, would always use epoxy; but I've used it forever and am comfortable (although never happy) using it. Epoxy is certainly more versatile, with an almost endless variety of characteristics available depending on the fillers you mix it with. I find it is just easier to have one product. But I can't think of any reason the vinylester would be inherently unsuitable.

But then, I haven't written a dozen books on boat repair.

Oh, and one note...Once you use epoxy I believe you are more or less committed to it. Epoxy will stick to almost anything. I don't think polyester or vinylester will bond properly to epoxy, though.