I have to ask. Why drop the mast? Capsize the boat and then either walk it under the bridge or sit on the bottom hull and paddle if it is too deep to walk. There is a race around an island in the UK every year and they do exactly that to go under the bridge linking the island to the mainland (which being the UK is also an island, but I digress

This seems so obvious I must be missing some key information there. Why do they have to remove the whole mast?

[Later edit: Video clips showing how it's done]