Just be careful not to wear a camel back when you're racing as you will probably end up with some a**hole protesting you! Perhaps it makes a difference to the very very top sailors but the difference is so slight that you would gain/loose much more by having the sails slightly out of trim or by steering a couple of degrees off line than by the extra 1kg on you're back rather than on the tramp. Not a rule that I agree with.
They're a great idea for recreational sailing though.
I'm just curious about this, because I thought water bags, camelbacks, etc. were made illegal for safety reasons -- too many racing dinghy sailors were injuring their backs in their zeal to reduce heel. I haven't seen any rule making it illegal to fill your trapeze harness or a backpack with helium to make you lighter.
