I am lazy. I just girdle the trunk once with the chain saw 1 inch deep. When I want to make sure it dies, I girdle twice about 2 inches apart & use a crowbar to split out the wood & bark in between the 2 cuts. I have never tried it from a boat.
From a boat, keep it quick & simple: girdle once about 1 inch deep. Depending on the tree, it may take a year to die completely.
