As to choice of drills. Rick beat me to the comment that an auger is too heavy to swim with, unless we are speaking of a bow drill, mostly wood and sinue, with a small mettle tip on the drill, easy to use in the water, if you find a nice nitch under the transom wedge yerself in under the rudder, drill between the planks likely butted back then, nice straight lead to drill into to, I like the reefing Iron idea as well, easier to swim with, however, the caulking would not likely be easy to get at with swelled planks, maybe you'd get some but don't forget oakum is being forced in by the presure of the water as the planks swell, better drill between the planks, and my vote is for a bow drill, Cheers, stay dry, Larry