Overcurrent Protection on Winches, Windlass, and Bowthruster


I certainly like the way Amel designed the SM, or I would not have bought one.  And this does not apply specifically to my boat, because the previous owner installed battery terminal fuses to cover the issue for me. But... there seems to be a basic misunderstanding about what a fuse is FOR in a circuit. 

Putting a fuse in the bowthruster circuit (for example) is NOT done to protect the thruster motor.  It CAN NOT prevent overheating or any other problem with the motor before the motor self destructs.  The fuse is there to protect the WIRING. 

Anyone who has ever seen a dead short across a 12 volt battery knows that wires melt, and burst into flame--even vaporize--when fully shorted.  Fuse and wire should NEVER fail under any normal load imposed by properly designed motor circuit--even an overloaded motor.  But when there is a dead short, things get VERY scary in a real hurry if there is not a fuse in the system.

Note that a fuse is very different than a motor with internal thermal protection. Most non-Amel thruster motors are thermally protected, and will be shut down by an internal thermostat if used too long and hard, and will not run again until they cool off. A non-thermally protected motor will not start a fire if it overheats, it will just melt  down and die.  Making the choice to not thermally protect the motor is a reasonable risk/benefit balance that will varies from one application to another.  It is a completely different choice, with completely different consequences than not installing a fuse.

BUT... maybe someone can explain to me why Amel wire runs are impossible to short circuit and therefore do not require fuse protection at the supply end?

If your answer is that Amel is always perfect, then I will show you how the fuel tank gauge was installed in my boat, and you can explain to me how that is the perfect solution...

Excuse me if I am a bit paranoid, but I have seen four boat fires, and extinguished three of them. (None my boats, thank heaven!) All three of those were of electrical origin.  Fire on a boat scares me way more than it frightens my insurance company!

Bill Kinney
Harmonie, SM #160
Port Canaveral, Florida