It seems I can't say it enough. Boat wiring needs to be properly protected against insulation chafing. The wiring you see in the photo below is yet another example of totally ignoring this little detail.
On the boat above the potential problem with no chafe protection is possibly lethal too. The white cables you see are actually AC power cables that are powered by shore power or when offshore the on board AC generator. Once the insulation on any of those cables gets chafed through, this boat will really come alive. The perimeter of the cut out in the aluminum you see is a sharp metal edge. A short circuit to the metal surrounding the cable run will charge up the entire hull and superstructure on the boat whenever the circuits in question are activated.
Its important for everyone to remember that these short circuits may or may not necessarily trip a circuit breaker. You need to remember that circuit breakers first of all don't trip at their nominal rating of say 10 or 15 amps. The actual trip rate is going to be somewhere around 125-150% of the nominal value. The second important point to remember is that just because the insulation gets chafed through to bare copper doesn't mean that the connection to the metal hull in this case is a good one, so the inherent electrical resistance in that connection will reduce the amount of amperage that is flowing to below even the nominal rating of the circuit breaker for the circuit in question. The bottom line? This fault will go unnoticed until somebody gets zapped! Look for these types of flaws on your boat and get them fixed asap.