Monday, 29 April 2019

DOH ! - Turning Vicegrips into an Arc Welder


The handle end of my vice grips

INTRODUCTION

Things are pretty hectic onboard Fluenta these days.  We have a lot of boat projects getting Fluenta and ourselves ready for the long passage to Alaska and colder, wet weather coupled with catching up on school and admin after over two months away from internet.  Despite the pace and pressure Elizabeth and I try to be safety conscience which is not surprising considering our professional backgrounds in engineering. That being said, we are just as liable as everyone else to have one of those all too quick "DOH !" moments ...

Inspired by SV Totem and The Boat Galley's recent posts on mistakes onboard, here is our story from yesterday ...

THE INCIDENT

In addition to adding things to Fluenta (like expanding our heating system) or fixing broken things (like our toasted wind generator and leaking port lights), we are doing much of the scheduled maintenance program early so everything is fresh for the passage.  These scheduled maintenance items are a treat, compared to trying to knock out port lights with a mallet, so changing the engine's raw water pump impeller seemed like a nice way to get something done but without much stress on a Sunday afternoon.

The challenge on our Perkins 4.236 engine is that there is not a lot of space between the raw water pump cover and the starter.  I replaced the raw water pump cover with a Speedseal in 2012 to make the job easier but I still need to get tools in to pull the impeller out.  I would love to use an impeller puller but there is no space. Therefore I need to resort to the dreaded screwdriver-prying and vicegrip-pulling method.

Near the end of the starter is the positive lead from the starter battery.  I have a cover over this in accordance with ABYC standards but if you are clever you can still reach a tool to touch the terminal and then the engine frame creating a very lively electrical circuit.  Therefore, being smart engineers, we always shut off the battery switch when working in that space.  I then proceed to pry, pull, curse and cajole the old impeller to come out.

I was already bleeding a bit, but that is almost SOP when I am working on an engine.  The impeller was slowly coming out, but then I slipped with my vicegrips and completed the circuit between the starter and the pump.  I jumped away as much as you can when lying on the galley floor but had to put my hands back in as the visegrips were stuck.  Liz could see the reflections of the arcing from the aft cabin and it melted bits off both ends of the vise grips.  I was rather startled but unhurt.

Looking at the gap between the raw water pump and the starter motor.  The Red "+" is the positive lead for the starter motor and the green "-" is the face of the raw water pump that provides an excellent path to ground for all those electrons stored in our battery bank.

How did this happen when the battery switch was off ?  Fluenta has three battery banks: the big house bank, a starter battery and the windlass bank.   The starter battery is generally only charged with its own alternator when the engine is running (the house bank has its own two alternators and the windlass bank is echo-charged from the house bank).  Our start battery needs to replaced as it is not holding a charge (despite being barely a year old bought recently in NZ - grrr !) so since we were running our little Honda generator to top off the battery's charge on a particularly cloudy day, I paralleled (i.e. connected the start and house bank with a big battery switch) the two battery banks. In my haste I had forgotten that I had done this.  I circumvented my own safety rules, and gave our 980 Amp-Hour (almost a thousand pounds of batteries) battery bank a chance to briefly discharge through my visegrips.  As I was lying there about to start the job I had even briefly thought about double-checking the voltage with the multimeter, but I had brushed that off as an unnecessary step so I could just get this job checked off the long list.

The other end of the vice grips.

Now 12 volt is unlikely to electrocute you compared to 120V but it sure could give you serious burns.  Ironically we had recently being talking about a blog post from the Boat Gallery where similar arcing led to a fire and could have led to the loss of their boat.

OTHER DUMB THINGS I HAVE DONE

As a side note, I have to confess this was not my most impressive or dangerous arcing.  Years ago the ship I was posted to, HMCS PROVIDER, was decommissioned and I got permission to go onto the ship and salvage the flight deck trafficator lights before the ship went off to Turkey to be scrapped.  I rappelled down the hanger face to get the lights themselves easily enough but then had the bright idea that I should get the control panel too.  The control panel was located several decks up in Flyco (the little control office overlooking the flight deck).  Easy. I pulled the circuit breaker at the base of the ladder, climbed up the vertical ladder several decks and started to trace the wiring for pulling the panel out. I could not find where it was terminated so I merely cut the wires with my trusty leatherman and was flung across the small space by the arcing.  I guess I pulled the wrong circuit breaker.  I cannot remember if it was 120V, 240V or 440V up there but it was a pretty stupid thing to do.  The ship was decommissioned so the only other person onboard was an elderly commissionaire security guard so nobody would have likely found me until I started to smell !  I gave the trafficator lights and panel to what is most definitely the best maritime aviation museum in Canada: the Shearwater Aviation Museum


The red arrow shows the location of FLYCO in PROVIDER.
CONCLUSION

What are the "lessons learned" (or as we used to joke sometimes in the military when we make the same mistake over and over - "lessons observed") ? I think it is a pretty good assumption that most folks working on boats know not to connect a positive terminal to a ground with their tools.  The obvious reminder is to de-energize any circuit you are working near when practical.  The less obvious lesson, but one many have learned the hard way, is that if you make a deviation from your standard operating procedures, you also need to rethink your safety precautions.  We rarely parallel the batteries, and I did not think of the implications of doing so and then working on the raw water pump.  Finally, a reminder to "check - not assume".  I could have avoided all this drama if I had checked the terminal with my multimeter like I normally do.  And the final, final reminder but pertaining to the incident in PROVIDER, don't let junior officers use tools without supervision ...
 

2 comments:

  1. Max,

    You are not alone...

    How fortunate you were both times... I've heard the actuarial tables on professional electricians demonstrate the most electrocutions occur to those on the job for more than 20 years... [I have never validated that, however...] Both times you did all the right prelim tasks; we all skip the verification steps on occasion when boat yoga taints our thinking [or resolve?...]

    My best recent doh was equalizing our 900AH FLA house battery bank. I forgot the battery combiner to the starting bank was on... until I detected that aromatic frying battery smell... I had boiled half the water out of the starter batteries with this mistake. They seem to have forgiven me this time, but time will tell...

    Related, I recently installed a brand new [USA made well known brand that doesn't begin with a Z...] inverter for a good boating friend. The same I installed in our boat in 2015, and the same I recommend to many other fellow boaters...

    All went as expected and his new house bank was properly charged for several weeks prior to his return. I poped over to demonstrate how to use the controll panel for the new inverter when I saw the red fault light come on— just two minutes after I had stepped onboard...

    I started accessing the menu showing fault codes when I once again smelled that delightful aroma of smoke escaping an electronic device we are all familiar with [but absent that BBQ like fragrance of human flesh...]

    The inverter had aparantly picked that precise moment to commit suicide through spontaneous combustion... [Nothing had changed in weeks...]

    As you know, the cases of such devices are designed to contain any fire that may happen, but small [6 inch] flames were licking out the top vents... I killed all power [AC and DC] to the unit, and used one of my messless Maus extinguishers on the flames.

    I looked at my buddy and said I may own you a new inverter if I did something wrong...

    I hadn't... the warranty replacement unit is arriving soon...

    Now to reinforce the fireproofing in the locker where my inverter resides...

    I don't know about you, but I can't wait for the next self imposed lesson observed...

    ReplyDelete
  2. Glad to know it is not just me ! I have almost done the cooked starter battery one too.

    ReplyDelete

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