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 is dark grey. Look at a pencil. Yes, because pencils use graphite, not lead. Though dark and very grey, I would say the hue of graphite is bluer than other shades of dark grey.