So I hit a bit of a snag with the plot. One of the characters is stuck on an island, it's not that there's no boat, but he's alone and the islanders are hostile. I need to find a reason he cannot just escape, like is it believable that the island is too far from shore? Even though it can be discerned in the distance? Perhaps there are some dangerous ocean currents that takes you out at sea and makes it difficult to navigate alone? I don't know anything about sailing so if anyone have any expertise in the area... The character is a seasoned sailor, btw.
I'd say the danger of braving the waters has to weighed against the danger of coexisting with the hostile natives. Which one is more likely to increase the character's lifespan?
Why not have the islanders prevent him from escaping, like what happened to John Renton. You'd be surprised what a small craft is capable of...
The boat has a hole in it and the water is full of sharks. Or there's a giant-ass whirlpool in between him and land. Or a giant-ass sea monster. Or maybe the weather is simply too bad.
Why does there need to be a working boat? I’ve been sailing, and I was in the Navy. Not exactly a seasoned sailor. - MC
If the island is surrounded by coral reefs there'd likely be strong currents. And corals are sharp (take it from one who knows...), so that'd be a good enough reason not to go anywhere near the reefs.
Stephen Crane's short story "The Open Boat" would give you very strong basic reasoning as to why it would be a problem. Breaking into the shore tide past the cresting waters is intensely difficult, especially with a small craft incoming from an ocean island. Also, the story is an excellent read.
All good suggestions. Perhaps there's a strong current and you really need two people to fight against it? If not, and you get exhausted, you risk being taken even further out at sea.