Over the past months, we had noticed that salt was creeping out around the handles of our seacocks. While hauled out for a bottom job and stern tube maintenance, I purchased the replacement seals kit for the 1.5 Inch Perko Seacocks on my 1990 IP-35 #99 and the plan was to replace the seals before launching. When we removed the bushing to access the handle seals, we found that corrosion had worn away the threads and with the newer seals, it was not possible to get enough grip to reinstall the bushing. I purchased two replacement seacocks and when we removed the old ones, we were shocked to see the extent of the corrosion on the original seacocks. See the attached picture. Note the amount of pink areas indicating a loss of zinc in these bronze seacocks. The shipyard told me that this issue could have easily sunk my boat. The bonding wires were connected so I didn't expect any issue other than planning to replace the seals in the original factory seacocks.
WOW WOW WOW. My only guess is that your bonding wire was connected to the seacock, BUT, the other end of that bonding wire was corroded or not grounded some where. Maybe you need to have an electrician check out your entire green bonding wires and see if they are all doing their job. After we came out of the factory refit in 2013 (original IPY factory team) we hired a marine electrical to check out our bonding wires. They all checked out perfect and we were happy with the refit, one item was the bonding wires.
Thank you for sharing these photos. This is something we all need to inspect and look into.
I agree with Hayden that this seacock failure was related to lack of continuity of the bonding wire back to the common point. A bonding test of all green wire connections is relatively easy to do using your ohm meter when the boat is out of the water. In addition to the ohm meter you need a single piece of wire long enough to reach all the green wire connections throughout the boat - about 15' for our 370 and an assistant to read the meter. With clips connect one end of the ohm meter leads to the common green wire bonding point which for the 370 is the shaft log where they are all held together with a stainless clamp. Clip the other lead of the meter to the long wire and set the meter to a low ohm scale, touch the far end of your long wire to the green wire bonding point and see how much resistance is in your meters path - this is your "zero base reading" - should be a few ohms at best. Now move the long end about the boat hitting all the green wire connection points - the DC common ground in engine space, all seacocks, rudder shaft ( 2 places) and so forth. Verify that you get an ohm meter reading near your zero base reading and be sure that you are touching the actual metal of the seacock or rudder shaft because there may be high resistance in the lug connection of the green wire to the seacock. We do this each season when we haul out and usually find one point to clean up.
The following user(s) said Thank You: hayden, jhstacy
Thanks to both of you for the advise. I have one of the corrosion meters with the AG/AGCL reference electrodes and it always shows each seacock as slightly overprotected. However, a lot of the wiring looks new and I think was replaced before I purchased the boat. I think the seacocks may have already been compromised before the wiring was replaced. I like your idea of using a multimeter to check resistance across all bonded metal and will do so before we go back in the water.