Boasun is correct. When away from the dock, you cannot count on any help with a boat fire. First and foremost is prevention! After that, is to have a good complement of fire extinguishers located where you may gain access to them quickly under various scenarios (such as galley fire, engine fire, etc.). Knowledge and experience in how to effectively use them is important to get maximum results. However, remember, fire extinguishers are for relatively small (incipient) fires, once the fire gains a good foothold, EVACUATE! Remember, life over property! Always keep an escape route behind you when you are trying to fight a fire. Preplan your actions (what would I do if???).
Just a few suggestions from someone who has fought his share of fires, yes even boat fires (never on my own boat),