Depending on the size of your boat you may need more than one. Boats less than 26' have to have at least one B-1 fire extinguisher on board. Boats 26'-40' need to have at least two B-1 fire extinguishers on board.
Graphite is an electric conductor, consequently, useful in such applications as arc lamp electrodes. It can conduct electricity due to the vast electron delocalization within the carbon layers (a phenomenon called aromaticity).
Graphite usually occurs in flakes in metamorphosed rocks rich in carbon, but it can also be found in veins and in pegmatites. Where large deposits are found it is mined and used as an industrial lubricant and for 'lead' in pencils. The crystallinity depends on the temperature of formation and the grade of metamorphism.