Lightning dissipation plate

[daviddiscenza]

Hi. A routine inspection showed that corrosion on the bolts and nuts holding the lightning dissipation plate in place. To my untrained senses, it appears that the material in the picture is wood. Is that really a good idea given the amount of current that would flow through the wire? Can anyone recommend a good replacement material to use and a source for it as whatever this material is, it's beginning to crumble?

Thanks for your help.

[Privilege]

I've been researching this recently so am interested to hear the replies of knowledgeable people. The plate on the exterior of the boat obviously has to be conductive so assuming that you don't want to splash out on gold or silver, copper and aluminum are all so in the top four on the list of conductive metals. I can't tell from your photo but either the plate is steel and there are rust flakes on it or the wood has just been used as a backing pad for the external metal plate.

[daviddiscenza]

Privilege, thanks for your reply. It's the backing material that needs to be replaced. I'd like to know what material I should use. I'm not looking to replace the dissipation plate.

[Orion Jim]

How about G10. I have no backing plate. I wouldn't think one was needed as the sintered bronze plate is under no strain.

[Frankly]

Use a piece of starboard as an insulator/ backing. I would replace the wire, and termination. Crimp, solder, and seal the wire to terminal connection and give the stud a good wire brushing before reattaching and if you have several studs connect them all together with some tinned copper sheet.

[daviddiscenza]

Orion Jim - what is G10?
Frankly - not familiar with starboard. What is it? I'll follow your advice regarding cleaning and reattaching the wire.

[Frankly]

Starboard is a marine plastic made in sheets (1/4 to 3/4" thickness). 2' x 2' pieces are available at most ship chandleries, or your local boatyard might have a scrap big enough for your job. It is in the polyethylene family so a good insulator. Probably not necessary but I am kind on anal when it comes to messing with Zeus. I want to try to make sure that current goes through that bolt(s) and not some alternate path that might sink my yacht.

I have 4 ea 1/2 silicon bronze bolts on my copper plate, and all 4 are connected to the mast with 2 short lengths of 1/0 cable.

G10 is epoxy FG laminate also good insulator.

[SailFastTri]

G10 is fiberglass board material. You don't need a backing plate, as the ground plate is not under strain and won't pull out through the bottom of your boat. Big stainless washers are more than enough.

[daviddiscenza]

Thanks everyone for your excellent replies. I've ordered a small sheet of the G10 from Defender.com. I'll sleep better with fiberglass in place instead of what I think is just marine plywood. I have my doubts, though, that the cable carrying the charge is up to the task of carrying 1000 gigawatts from a direct strike.

[SailFastTri]

Originally Posted by daviddiscenza

Thanks everyone for your excellent replies. I've ordered a small sheet of the G10 from Defender.com. I'll sleep better with fiberglass in place instead of what I think is just marine plywood. I have my doubts, though, that the cable carrying the charge is up to the task of carrying 1000 gigawatts from a direct strike.

#8 AWG should be adequate to dissipate one strike, #4 AWG should be adequate for repeated strikes.

[CarlF]

I would be more concerned about making sure you have a good electrical connection to the plate. I would cut off the wire connectors and strip back to shiny wire before attaching new marine (tin plated) connectors.

Bolts like this often corrode and break off where they attach to the plate. If the plate and bolt are embedded in something like 5200, everything can look fine with no electrical path. The best repair would be to drive the bolts out with a punch and replace the bolt if there's any sign of corrosion (copper or marine bronze bolt). This is likely to drive the plate right off the hull but it would be good to clean it up. Then re-attach the plate with a good adhesive caulk.

There's virtually no load on this plate so you could just use some good size washers on the inside of the boat and forget about the backing plate. Or use an epoxy like G-Flex in the bolt holes to both attach the plate and seal leaks (with a nut and washer as belt and suspenders). You can remove the bolts from the epoxy by heating a bit.