If I calcuated right, one gallon of water weighs 8.35 pounds, so to get 100 pounds of flotation you need 12 gallons. One liter would weigh 3 pounds or so. How much flotation is needed? I put sealed bulkheads in my Tred Avon, and tested it by filling the cockpits completely (hard enough in itself) and sitting on the stern, with my son sitting on the bow. It passed admirably!

> If you want cheap, temporary floatation, you can't do much better than
> empty 1 gallon milk jugs with the screw on tops. I just cram as many as I
> can fit into the front and rear, thread through the handles with some
> light rope as you go so they can't all get away, then brace across the
> hull with a fitted scrap of stick or two to hold them in place. For light
> duty paddling, I'd be satisfied with that.