In 1949 Chris Craft did not, as a routine, install several safety features that are today considered standard equipment. We’ve already discussed installing a bilge pump and an engine compartment blower. Now I’d like to show you the fuse block I installed for this 1949 Chris Craft 17 ft. Deluxe Runabout. No electrical system, marine or otherwise, should ever be contemplated without some form of circuit protection. Circuit protections is just that—it’s there to protect the circuit from electrical overload. That means the conductors (wires) as well as the appliances.
Circuit protection is generally accomplished by way of fuses or circuit breakers. Both work equally well. Circuit breakers don’t require replacement each time you trip one. Just flip the breaker back on once you’ve located and corrected the problem, and you’re ready to go. Of course, fuses only work one time. They burn out and you have to replace them. On the other hand, it’s easier to fine-tune your circuit protection using fuses. They are available in smaller gradations. Circuit breakers are generally available in 5 amp increments (5, 10, 15, 20, etc.) Fuses can be had for just about any load you want to specify—6 amps, 7.5 amps, etc.
According to the ABYC (American Boat and Yacht Council, a standards-setting body for the marine industry), circuit protection should be designed primarily to protect the conductors. So make sure you don’t melt the wires first, and then make sure you don’t accidently overload the appliances. Critical load appliances like bilge pumps and blowers should have the manufacturer’s recommended circuit protection stated on the appliance somewhere. In that case, the manufacturer’s recommendation takes priority. Design the circuit and its protection to accommodate the appliance. Size the wire a bit larger than needed, then choose your fuse or circuit breaker to meet the manufacturer’s recommendation.
In our case, there were enough “oddball” loads required by appliances that we elected to use a fuse block with a large “master” circuit breaker to cover the feed wire for the fuse block itself. A larger, more complex installation on a more modern boat generally uses a circuit breaker panel in conjunction with fuses for individual appliances.
You’ll notice there’s not a fuse for the bilge pump in the fuse block. That’s because its dashboard control switch comes with a built in fuse holder–a pretty common setup.