I have had one through hull
break off in my hand, and I simply drove the attached bung into the hole to plug
During my circumnavigation
, I carried a big fist size gob of pliable wax that plumbers use to seal toilets at the base of the toilet. It's sticky stuff that doesn't stick to fingers, but will stick to the hull when wet. I never used it, but I figured it might come in handy if I lost
a prop shaft with a gaping hole in the stern tube. I could cram the waxy stuff into the hole.
I carried underwater patching compound - also never used it.
One of the reasons I selected a catamaran
to sail around the world was because of collision
bulkheads. Mine have been tested. When my boat was delivered to the USA, the delivery captain
knocked a six inch hole in the bow from striking something in the water
. The collision
bulkhead limited the ingress of water
to only a few liters because the bulkhead is about eight inches back from the bow.
I also have five "watertight compartments" in each hull to isolate a leak from flooding that hull.
Patching a leaking hull in anything but calm conditions has a low probability of success. Most of the time, big leaks
quickly overwhelm you before you can do anything about them.