Wednesday, March 13, 2013

Bonding Boat Parts - FAIL

I don't care if your boat is brand new or 100 years old, there is always something to fix or adjust on a boat.  I've been boating for 42 years and have owned seven boats, not counting dinghies and Sunfish.  Some were new, some were middle aged, and some were old.   I never lacked for something to do.

Two days ago, I (finally) painted the decks after procrastinating for at least six months.  Yesterday, while showing Drift Away to a nice young couple, we were in the engine room.  We heard something dripping.  I got the light on it and saw drips coming from the intake filter for the reverse cycle A/C units.  This filter keeps out fish, reeds, barnacles, silt, and other crud.  I had just pulled the strainer out a couple of days before and I thought I just didn't get the lid on right, something I had messed up before.  There are two wingnuts on each side of the lid, and if you don't get them just right, the lid gets cockeyed and leaks a bit.  I just blew it off, but decided to fix it after the nice young couple left.

What I  found was NOT a leak around the lid, but a leak from a pipe fitting going into the pump.   I must have bumped it real good when I cleaned the strainer.  I reached down and wiggled it, and it came off in my hand!  I now had a 3/4" hole in the boat and a pretty decent stream of water gushing in.  I turned off the seacock and the water stopped, of course, so it was no big deal.

Take a look at the photo below.  Take a close look.

See the white plumber's tape?  That's the part of the pipe that was outside of the fitting on the strainer. So where are the threads that were inside the female part of the strainer?   Gone.  Gone, as in electrolysised away.

Like many, I'm pretty fuzzy on bonding.  Some articles I've read insist that all metals in contact with seawater must be bonded by being connected to the boat's ground, and others say nothing should be bonded.  Which is it?

In this case, the strainer body was bonded.  But look at the pipe fitting, which is about six months old.  It has plumber's tape on the threads, which effectively isolated it from the bonding system.  The result was a severe thinning of the inside of the pipe, and one small bump and the pipe broke.

Dave's tip 'o the day... if you're going to own a boat, make sure to get a heat gun.  A good one.  The kind used for stripping paint.  The kind that will set wood on fire if you're not careful.  I used the heat gun on the hose on the left to pull out the nylon barbed fitting, something I wouldn't have been able to do without it.  I also used it to heat up the metal elbow to remove the nylon fitting from the old elbow.

In the past, I've used the heat gun for many things, but probably the most valuable was to free up sea cocks that hadn't moved in over 20 years.  Just loosen the lock nut, heat the valve body up with the heat gun, and then tap the lock nut with a rubber mallet.  Works every time.

This is the replacement, bought at the local hardware store.

Here it is installed.  No leaks.  Man, I'm getting good.

So now I need to figure out how to bond this little section of pipe.  Seawater acts like a big battery, and any metal not connected to the bonding system will erode quickly.  I can run a wire to it from the bonding wire connected to the nut at the bottom of the photo, I suppose.  Maybe better would be to try to find a nylon 3/4" pipe and 90 degree elbow and put this matter to rest once and for all.

Sadly, no time for a victory beer.  I had to take the dogs to the dog park, and then pick up Pam at work.  We decided to go to Fox's Pizza for dinner, though, and a victory pizza washed down with two glasses of victory merlot also works.


  1. Dave, If I'm telling you something you already know, I apologize, but if that ell and nipple came from the hardware store, they're likely made of brass, and even if it's bonded, brass has a real propensity to dezincify in a salt water environment. That could lead to the same failure, perhaps sooner. Your best bet is to either get those parts in marine bronze, or as you indicated, use non-metallic parts.

  2. I don't think it's a bonding issue. As others have pointed out over on the CSBB your hardware store plumbing fittings are brass. Brass is an alloy of copper and zinc which when placed in contact with salt water becomes self destructive. Glad you caught it.

  3. You could have said that the bigger lesson is to make sure your sea cocks are in good working order. All the time I read of people who try to close their sea cocks only to find them frozen.