metal plate on bottom of boat

Craig G · Post by **Craig G** » Feb 1st, '12, 21:55

Does anyone know what the rectangular metal (might be copper or bronze) plate is for on bottom of hull. On my Bahia Mar, it was located just to the starboard side of the bottom of the hull forward of the engines. It fell off while sanding the hull. It appears to have only been holding on with some RTV as the 2 screws holding it on were rotted away. There were no wires attached to it going to the bonding strip or anything. My boat does have a transom zinc wired to the bonding system. Just wondering what I should do with it. I'm thinking of not reinstalling it, and filling in the holes?

Thanks

Tony Meola · Post by **Tony Meola** » Feb 1st, '12, 22:01

Sounds like it might have been a grounding plate. Usually used for single side band sets or to ground everything too for lightning protection.

Brewster Minton · Post by **Brewster Minton** » Feb 1st, '12, 22:25

Grounding Plate. My LPS ( Lightning Protection System) is hooked to it plus radios and radars and gps. Maybe put a new one on and use it?

Bertramp · Post by **Bertramp** » Feb 2nd, '12, 06:32

Craig....
Where did you haul ?

Craig G · Post by **Craig G** » Feb 2nd, '12, 07:34

Thanks guys. It would appear that it is a grounding plate for lightning protection. After doing some research though, that grounding plate is not really adequate for lightning protection. I think I will just leave it off and fill the holes.

Rawleigh · Post by **Rawleigh** » Feb 2nd, '12, 09:11

In most boats it is used for bonding. Transom zincs are useful, but are aftermarket add on's (at leaat for the earlier boats).

Skipper Dick · Post by **Skipper Dick** » Feb 2nd, '12, 14:28

There was one on my boat just off the starboard center line. I ignored it for the longest time and finally took a look at it hard one day and noticed that the former owners bottom painters had painted it up good, which is a no no. So I replaced it. The old one was not even hooked to the grounding system or anything, but I re attached it on the new one. I am almost certain that it was of little consequence to have it, but this part of Florida is the lightning capital of the world.

The bottom of the plate looks like a wire brush to create more area exposed to ground, but once it gets painted over, it is curtains for the plate. So if you replace it and have someone bottom paint, be sure and tell them NO PAINT on the plate.

Dick

Craig G · Post by **Craig G** » Feb 2nd, '12, 17:48

So if I re-install it, should I hook it up to the bonding system even though I have a transom zinc? Or should I attach it to my stainless steel marlin tower as a ground for lightning protection? Or just not use it and fill in the holes?

Charlie J · Post by **Charlie J** » Feb 2nd, '12, 17:59

i would tie all your grounds into it, if you have everything grounded now, look for the common wire that has everything tied and connect it to the plate

Craig G · Post by **Craig G** » Feb 2nd, '12, 18:08

When you say all the grounds, do you mean the bonding system also?

Brewster Minton · Post by **Brewster Minton** » Feb 2nd, '12, 18:09

Craig G · Post by **Craig G** » Feb 2nd, '12, 18:18

what are your thoughts on tying it into the stainless steel marlin tower to act as a lightning rod to ground as well?

Brewster Minton · Post by **Brewster Minton** » Feb 2nd, '12, 18:24

I would say yes.

Craig G · Post by **Craig G** » Feb 2nd, '12, 18:44

OK, thanks. I will clean it up and re-mount it tomorrow as opposed to glassing the holes in. I am on a roll eliminating holes in the boat. I just eliminated two seacock/thru hulls for sink drains, a drain plug in the bottom of the hull, and a large transducer that wasn't being used anymore which had two large holes and two half inch holes.....all glassed in!

Craig G · Post by **Craig G** » Feb 2nd, '12, 20:38

Steve, I am at Angler's Ave. Marine center.

Rawleigh · Post by **Rawleigh** » Feb 3rd, '12, 11:05

The ground plate is made of sintered bronze balls, which means that it holds water like a sponge, thereby having a much greater surface area than its physical size. The small balls (like bird shot) are heated in a mold until they just start to melt on the surface and stick together. That leaves the air (water) spaces between the balls intact. Painting it seals these spaces from the outside water, thereby rendering it useless.

In Memory Walter K · Post by **In Memory Walter K** » Feb 3rd, '12, 12:53

My problem has always been severe barnacle growth on the bare metal when I haul.

Craig G · Post by **Craig G** » Feb 3rd, '12, 21:27

Thanks for all the info, guys.

Rocky · Post by **Rocky** » Feb 4th, '12, 09:48

I remember a rather in depth discussion on grounding plates in the past and found the old post, there is very good info on this subject with the faithful
having good knowledge on how it all works. Thought this might shed some
electrons your way!

http://bertram31.com/newbb/viewtopic.ph ... 608822b99b

metal plate on bottom of boat

metal plate on bottom of boat

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