Burned by hot diesel deck fill cap

[BobAthensGA]

We purchased our '88 C34 last October and I have been a regular visitor to this site but have now figured out what I need to do to post etc. I wanted to share a very strange thing that happened the other day. I purchased 5 gal. of high sulfur off road diesel to take to the boat. Once it cooled down outside I went and got the diesel and set the can in the cockpit. I unscrewed the deck fill and turned around to get the can. When I turned back around smoke was really coming out of the deck fill. This was very alarming. Two dock mates were on the boat and the wife was in the shower below. One ran below to turn off the battery selector and the other undid the shore power cords. The engine wasn't running so we were trying to stop sources of ignition. Smoke continued to build. All water has stopped in the shower so wife is covered with soap with two other men on the boat and we are calmly telling her we may have a fire. More smoke. I decided the smoke might be building because I was letting oxygen down the deck fill. I grabbed the cap to replace it. The BB chain that holds the gap burned into my hand. For two weeks I have had nice little BB blisters on my left hand. I managed to get it screwed on and went below to see if smoke/heat/fire was in the cabin. The other guys said no but I had to check. Nothing. Ran wife out of head and opened panel under the sink to see if the diesel tank was hot etc. It was not. We were perplexed.

Decided it must be electrical so I got out the volt meter. Connected AC didn't read any stray volts in the rigging, life lines etc. Then turned on DC and began to turn on switches. Once Cabin Lights switch was turned on the Life lines, stanchions, Backstay all showed 12.5 plus volts. So I have a wiring issue. Why did the deck fill heat up??? After what my wife said was hours of endless discussion we determined the deck fill was reading negative and the stanchions positive. Then it hit me. I put the deck fill cab against the stanchion to hold it out of the way. In doing so I crossed negative and positive creating a short. We tested our theory and in seconds the chain had heated up.

I drew a "map" of all the stanchions, standing rigging, etc and tied the negative lead of the volt meter to the battery post on a long lead and went around and measured everything. Through a long process I narrowed the location to midship starboard side. By disconnecting the life lines I determined that voltage was running up 3 stanchions on the starboard side. Lifelines may have been hot because they are old and cracked and metal may touch metal at the stanchions. I was perplexed as to how voltage would be in 3 different places. With a flashlight and a mirror I found what looks to me to be an undersized cheap piece of blue wire that is running along the starboard side to each light fixture. This wire in conveniently pinned under the backing plate and/or washers of each stanchion and after removing one stanchion I could see a very small break in the insulation.  This wire appears to be original and may have always been pinned under the stanchions.
What I learned:  Go around the boat with a voltage meter and see if I have other items that are "hot".  Try to eliminate as many variables as possible. Map out the boat so you can keep up with what you eliminated. Repel the urge to go after the "I know it must be this item" unless you have deduced that it is that item. Have a good voltage meter and a long piece of wire you can tie directly to the negative post on the battery so that you can  go from bow to stern with the meter and have it grounded to the battery.

I don't know if this will help anybody else out but I thought it was a strange enough event I would share it.

[Ron Hill]

Bob : Good for you in identifying the problem AND finding the solution.

You are not the first person that has had a HOT fuel fill!!  That was posted a few years ago, but I don't  recall the poster ever giving us his/her solution.

There was another similar post of a MKII owner where the deck to hull captured the AC wire from the deck plug and eventually wore thru the insulation so the + and the - wires were close and heating up!!

There was also another case of the nav light wiring wearing thru in the compass binnicial and causing stray voltage to move down the steering mechinism and out thru the stainless rudder column - eating away at the stainless column at the water line!!

Watch out for those blue ground wire connectors!!

A few old thoughts (sure wish we had spell check back!!) 

[Les Luzar]

Bob,
Thanks for sharing your experience. I never heard of anything like this, but I will surely keep this information in the back of my memory bank! You just can't learn enough when you own a boat! You gotta love this website! 

[Bobg]

Thank you for that very detailed piece of information, I will check my boat next time I am up there, boats always can suprise you.