Have a question on the bonding...

[Bob_440_DA_w_Ca]

Have a question on the bonding system on a 1994 440 Sundancer.  I recently noticed a bonding wire corroded off at the eye crimp on one of the two lugs on the hull zinc on the transom (inside boat) so only one wire is connected to the hull zinc.  All wires go to one long terminal block and then two short wires go from the block to each mounting stud of hull zinc.  I have no idea how long this has been this way but probably a long time.  My hull zinc is being used up and changed every 5 to 7 months and is evenly eroded away so does not seem to effect it with only one wire connected.  Very hard to get to, way low behind gen.  I tried to fix and the bolt was brass and of course twisted off.  Tried to drill and retap but no go.  Just can not reach it well enough.  Drilled it but ran off side.  Did I need to worry?  I thought about some conductive epoxy and epoxy in a stud to hook up too?  Would that work or is that necessary.

[fwebster]

No, You need to repair this properly. The bolt is really the mounting bolt for the zinc.. From the inside going out there is the bolt head, the ring terminal for the ground wire, then the bolt passes thru a bronze sleeve then a flat washer is against the hull followed by a nut, then another nut then a flat washer then the B-12 zinc, another flat washer and another nut on the outside. All this forms a stud for the zinc to mount on. To change the zinc, you must hold the middle nut with an open end wrench then remove the outside nut to release the zinc.

Repairing this is going to require the boat being out of the water. And, the fasteners are bronze not brass.

[Bob_440_DA_w_Ca]

Thanks for this explanation. I could not figure out exactly how this all worked going through the transom. I should have left it alone not knowing so now I have an expensive mess I could have avoided. I am worried it could break loose and hole the transom underway. So far it has been this way for several months and no drips or any thing and the hull plate was just changed so maybe lucky. How serious of an issue do you feel this is in terms of getting it repaired ASAP? Thanks for the great help.

[Bob_440_DA_w_Ca]

One more point. I will be needing to haul the boat next season so could I wait that long to repair.

[fwebster]

Not seeing what the attempted repair looks like on the inside, it is hard to tell how serious this could be.

In a worst case, you disturbed the bedding of the bolt/stud in the transom....and this seems likely from your discription of the drill bit walking off the bolt head. However, water leaking inside the boat isn't the real issue. If the bedding is disturbed, the bolt could well be leaking into the transom. Due to the depth under the water, there is some pressure on the hull forcing the water in. That same pressure can cause water to enter the transom structure and cause a delamination between the layers of fiberglass. That can easily turn a simple rebedding job into a fiberglass repair that is 12" X12" or larger when you have to grind out the delamination and re-lay fiberglass in the area then redrill the zinc mounting hole.

I had this happen when an inexperienced yard guy was told to remove the transom zinc on the next boat over in the boat yard, got confused and removed mine by mistake, then crushed the transom by over-tightening the wrong nut when he put the zinc back on. Mine was underwater for 9 months when we found a leak inisde the boat and the delamination was 12" X 16".

I wouldn't wait a year to tend to this.