As i recently used this method i thought that it is useful, and would like to give it as a tip.
Now, one of the more annoying things in the game are rats. They eat (or spoil) anything you can carry. Food, weapons, cargo. They are a REAL pain and very annoying.
Here's how to deal with them. You'll need some cash to get this done. Say, 30 to 50k, depending on how costly the prostitutes you like are.
Go to a brothel, the cheaper the better. Port Royale is expensive. I used the one on Martinique.
Find a lady inside and tell her that she is the most beautiful creature you've ever seen. If she tells you to quit the sweet talk, go to another lady. If she likes your flirting, note the name.
Now, go to the madame and tell her the name of this woman that you want. You then go upstairs for some rather silly moaning and a CENSORED screen. You must do this at least five times. DO NOT leave town during this sequence else the lady may leave the brothel. Instead, have sex, go sleep in the tavern and repeat. You will lose some reputation.
Beginning with the 5th encounter, speak with the lady after sex. Sooner or later (5-8 tries) she'll tell you that she has fallen for you and that she has information that may be important. She'll then tell you the location of a treasure that another captain/customer told her of. Write down the name, it will not appear in your logs.
There are four potential locations for this treasure. From just North of Peurto Bello to North of Belize. If you have trouble finding it, there's maps here at Pirates Ahoy that show where everything is. Or just ask me and I'll tell you. This could be considered mildly cheating - this is what all those in-game maps are for. So, use those if you want to play it straight.
Anyway, when you find the location look for the Rat God totem in a chest. There is nothing to fight at the destination - just and ungaurded chest. Sometimes on the beach, sometimes in the caves. Sometimes there might be another totem laying around too depending on location. As long as you keep it on you, the rats will never bother you again.
this can be done early in the game and is very important for merchant type players, but useful for others too.