I was going to enjoy an unexpected and lovely day yesterday by going for an unplanned and impromptu sail. It didn’t turn out that way. As I was preparing for departure I unplugged the shore power cord, which turned out to be a real bear as the plug had partially melted onto the receptacle.
THis could have caused a fire!
I was glad to discover this as it’s quite a dangerous situation. Its a typical problem especially once the weather turns cold, as our electric heaters draw a maximum amount of power through the system, and any weak points reveal themselves. That cord was less than a year old, and I knew the boat’s receptacle was the problem.
You see, as the contact metal in the receptacle ages it corrodes, which increases electrical resistance. Recalling Ohm’s law E=IR, where E is the voltage drop across a conductor. Using this we see that E increases as either the current I or resistance R increases. When we turn on the heaters I is at a max, but hopefully the R of the plug connection is zero, so Voltage drop E across the plug is also zero.
But as soon as corrosion gives a value of R greater than zero we get a voltage drop, which becomes heat. The greater the value of R or I, the more heat until stuff starts to melt and the possibility of fire occurs.
Keeping the R of the connection at zero is a real problem, especially since the boat’s receptacle is on a bulkhead in the anchor locker, waaaay back where you really can’t reach it to sand the contacts clean. In fact I’ve always hated that location for the receptacle because in order to connect or disconnect the shore cable you had to lie on your belly and reach as far back as possible, and you could never plug the cable in properly. The build quality of CS yachts is superb, but that was an incredibly stupid place to put the thing.
So given that the receptacle had to be replaced, I was determined to move it to a better location (I’ve wanted to do it from the beginning but the parts are pricey and I’m rather lazy). I’ve also been aware that the internal power cable was solid wire which is another no-no in a boat, although usual in 1980.
First thing to do was decide where the plug should go. I decided on the top edge of the coaming to make access easy, reachable from either end of the boat, out of the weather, and not in the way when we have cockpit parties. I also wanted it to be as close as possible to the boat’s distribution panel.
Once that was decided, the first thing to do was cut a hole for the new receptacle.
Unfortunately, I no longer had power to the boat to run the damn thing, so I cut off the damaged end of the shore cable and did this disaster. An appalling thing to do but I had no choice.
Don't try this at home!
Once you have the hole cut out, it’s crucial to remove the balsa core around the hole and replace it with epoxy. That way if the seal ever goes, water cannot getting into the core and rot it.
Cutting away the core
Core removed from the edge of the hole
Once the core is removed, you mix up some epoxy and filler. I had some epoxy leftover from a long-ago project and although it had discoloured, it still worked okay.
Epoxy and filler
The mix should be a very thick paste so it won’t slump out. You need an applicator that is flexible enough to fit the contour of the hole. I used a piece of thin cardboard.
Thick epoxy past ready for filling
The edges of the hole are filled with waterproof thickened epoxy so the worst that can happen if the seal is not maintained is someone sleeping in the quarterberth gets wet.
Edges of hole sealed
The cable 3 wire 10 gauge cable is attached to the receptacle and threaded through the hole. Screw holes are drilled and the screw threads are sealed with marine caulking even though they also pass through the rubber gasket.
Receptacle in place
Then the electrical panel needed work. The old solid wire cable was disconnected, taped off, and rolled into the hull. Normally I would pull it all out, but the other end is unreachable to disconnect. You can see evidence of previous problems with corrosion by the burnt plastic.
The old cable must go!
I decided to use a piece of the shore cable as my internal wiring, because I believe the quality is superior than standard Romex. I also cleaned up the bare grounds from the other wires. I need to find a grommet where those cables pass through the box. Tsk.
New cable installed.
With the boat’s wiring completed, I decided to repair the shore cord. It was less than a year old, and with the price of copper taking off, new ones are approaching close to $100. I decided to use both a waterproof housing as well as replacement plug even though the receptacle is inside the boat’s enclosure. These two parts were still 1/2 the cost of a new cable.
Waterproof housing for plug.
Assembling plug components
The cord is warranted for another 4 years, and if by some unusual and unlucky chance the plug burns out again, just the plug itself can now be replaced for 1/3 the cost of a new cord.
Plug assembled and cord good for another 4 years
I was grateful for the warm, sunny day to do this. As you can see from the picture I finished just as it was getting dark (and cold). Hopefully that repair will last this boat another 30 years.