The Question and Answer section for Treasure Island is a great resource to ask questions, find answers, and discuss the novel.
It sounds like a good idea. Deciding that the pirates will soon take the anchor up and wanting to stop them, Jim decides to cut the Hispanolia loose and merely let it land anywhere the wind and current take it, thereby stopping the pirates.
He certainly is dirty and looks like a pirate. He is an old, brown, dirty, ragged seamen with a sabre cut on his cheek. I'm not sure how he doesn't look like a pirate.