Find a concrete patch or a dumpster, make a couple of fires and use the oldest extinguisher to get a feel for how they really work.
Your first surprise will be that they make a huge cloud of dust that gets in your lungs and eyes and all over the place. When used down below, the boat will be full of that for weeks, no matter how you clean. You'll want to hold your breath and squint your eyes while using it. And typically, one "under the desk waste paper can" is about all the fire they can put out.
The bicarbonate ones are also sold as "garage" extinguishers, because the yellow powder is badly corrosive to electrics and appliances
. So you may want the legally required marine
extinguishers on board, but after that? WalMart or Home Depot sell perfectly good alternatives at way less than marine prices. The "USCG Marine Certification" mainly means there's a different bracket for the extinguisher, and those still suck. So, no need to feel guilt about not getting more of them.
I used a CO2 bottle when some camping things were self-combusting in my closet one evening. Apparently the hurricane
matches wanted to turn the tent fly into a group poncho for the seven dwarves. I didn't ask what was burning, just cracked the door open enough to stick the horn in and blew CO2 at it. And while that would be a Class A fire that Co2 can't put out...it did very nicely, and saved a wicked cleanup.
You may also want a "kitchen" extinguisher for the galley
. These are bicarbonate, something fairly new from Kidde, using a different head
to dispense the powder at lower speeds over a wider area, so it doesn't spread burning grease, and won't cause corrosion
problems. The same $17-20 that all the "liter" sized bottles run, discount.