I only ever used a single layer of 2 inch 6 oz tape inside and out. I don't think a double layer on the inside would make any difference in regard to strength, provided the fillets are adequate.

The outside corners are where any wear might occur, but that goes for cloth as well.

I omitted to mention previously that I did always saturate the rest of the boat with epoxy before varnishing. I never had any water penetration problems. In those days I had not yet discovered the heat gun, and I imagine a quick blast with the heat gun on the first coat would really get that plywood well and truly sealed, at the risk of adding a few extra ounces in weight.

I have become a fan of 4 oz S-glass over the last three builds, and as Nick says, it doesn't add a huge amount of extra weight. I would imagine around an extra three lbs in cloth and resin perhaps.

The main big benefit of just taping for me these days, would be a fairly significant saving in S-glass, which is not cheap over here, and a bit of a saving, not much though, in epoxy.

In the early days I built my own because I could do it cheap, and I had no money. A completed boat used to cost me around £70 to£80, and I was not much concerned with finish or cosmetics. I don't know how many boats I have left in me, I will be 60 next year, and now quality and finish have more significance for me, so I don't really count the cost. Even the very best materials are substantially cheaper than six or eight months of evenings in the pub. That is what I tell my wife, anyway.

Et.