John,
I did not find any bonding screws on my head-related sea cocks, to which my grounding system could have once been attached. Those sea cocks bore the original paint splatters from the original inside hull spray painting. My cockpit thru-hulls were more recent additions and they did not have bonding screws either. I have no other metal in the water other than a rudder shaft (upper and lower)
I have crawled around quite a bit under my cockpit because I had to deal with some leaks from the lazarette into the cockpit lockers and because I installed Garhauer lifting davit and that required work below the cockpit. I can think of no conceivable way to tie the general grounding system electrically to the rudder shaft beneath the cockpit since the rudder shaft slides through its spiffy water-tight glassed-in tube. It would seem an easy thing to do to attach a grounding plate to the hull below water just aft of the lazarette bulkhead and use that as a grounding plate, but the more I read on this topic, they more I am becoming wary of bonding my currently isolated metal components to what would amount to a giant anode, lightning not withstanding.
My rudder shaft is now well connected to zincs, so it is protected.
There were no zincs on my boat when I hauled it. I have been hauled out three times in the past month under rather bizarre circumstances. August was a nautical version of Bill Murray's Groundhog Day. I am hoping to be back in the water on Tuesday.
I have not previously had the boat out of water, so this has been a process of discovery. I discovered two screws that obviously had zincs at one time. One is on the rudder shoe and the other on the rudder. I sanded the bottom paint off the rudder to access the nuts to tighten the bolts connecting the rudder to its upper and lower shaft. I also stripped the upper and lower sections of the bronze shaft. The zinc screw on the upper portion of the rudder seemed strange until I opened the lower of the two upper shaft bolt inspection holes to tighten that nut. An ingenious copper plate with two holes drilled in it connected the upper bolt to the zinc screw. The photo below shows that device. The zinc screw is visible in the photo. The copper strap spans the inspection hole on the starboard side of the rudder. The zinc screw is simply screwed through the smaller of the two holes in the copper strap and into the body of the teak rudder and must at one time have held a zinc of some sort. I replaced this screw with a bolt that goes completely through the rudder and is used to connect a traditional two-sided "balanced" rudder zinc as pictured in the first post to this thread.
The strap runs forward and then bends 90 degrees at the location of the bolt in the inspection hole. There the bolt is inserted through the larger of the two holes in the copper strap. So, the strap on the bolt end serves as a washer between the nut and the forward wall of the bolt inspection hole.
In line with that old song about them dry bones, the zinc bone is connected to the copper strap bone, the copper strap bone is connected to the lower of the two upper rudder shaft bolt bones, and the lower of the two upper rudder shaft bolt bones is connected to the upper rudder shaft bone, and the upper rudder shaft bone is connected to the tiller head bone. So although them bones may not be dry bones, the zinc protects them all from all things wet and briny.
Since the rudder shoe and the lower shaft are in contact, albeit with a mess of blue grease between them, I assume that the rudder shoe zinc protects them both.
However, these two zincs of mine as pictured in the first photo on this thread are rather small, and my upper rudder shaft does have a pink cast to it in places indicating some past corrosion, so I will have to dive the boat from time to time and replace the zincs as necessary. It would have been tempting to add a larger zinc on the rudder shoe, but the need to fit a zinc in between the bolts limited the size of the zinc. I am interested in knowing if anyone else has added larger zincs in this area, o on teh rudder for that matter.
And by the way, while I was working on my rudder I removed the gudgeon and replaced the bolts holding the gudgeon to the keel. I just slipped new bolts into the holes and attached washers and nuts without a second thought, but now I am wondering if it would have been appropriate to have bedded those bolts somehow.
The holes are rather tight, but if those are merely holes drilled through the hull laminate and/or through any voids, might they not allow water to enter the laminate? I wonder about this because little blue dribbled lines run from the gudgeons downward indicating that water must have drained from them for some time after my third and most recent haul out this month. ( not a lot of water, mind you but water that left the blue residue of what I presume is copper oxide formed from some reaction between the fluid leaking out and the new Trinidad red bottom paint.
The old gudgeon bolts were shot. The nuts twisted off rather than releasing. They were bronze bolts like my new silicon bronze bolts. I saw no evidence of bedding compound on the bolts. Since the holes are very tight, I am not sure how one would effectively bed them anyway. One could, I suppose, drill the holes out to a larger diameter, filed them with epoxy, and then re-drill them. I would like to think that those holes do not permit water to enter the hull laminate, but now I am having doubts about that issue.
Does anyone out there know that answer to this question? It would seem that Pearson would have thought the gudgeon bolt hole arrangement out a bit, especially given the keel void issue discussed on page 40 and following in the Ariel manual. I could not find reference to the gudgeon bolt issue in the Ariel Association manual. Since I have similar blue dribbled lines running from various places on my rudder which wouild naturally absorb water saince it is teak, this concern of mine may be much worry about very little that should be worrisome.
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