Ground Plate

[Richard G.]

Seem to have developed some leakage from the grounding plate on my CD 27. Does anyone know what the material is that is between the hull and the backing plate, which is wood? The wood is quite wet and it is the first time that I have noticed this.

Thanks,

Richard

[Ron M.]

Hull is fiberglass, roving and mat about 3/8" in that area.
Replaced the wood backing board for my ground plate with 1/2" FRP a few years back. rounded all edges as that material is sharp ! Caulked well with 4200, particularly both sides of thru bolts. Slight countersink to all sides of holes in hull and backing plate.

[Richard G.]

Ron,

Thanks for your reply. Did you have any black material, almost like roofing paper between the hull and the wood backing plate?

Thanks.

R

[Ron M.]

can't recall. Proper cleaning and caulking should do the job. Clean everything with solvent. No leaks in 5 yrs.

[Richard G.]

Thanks again.

R

[Maine_Buzzard]

I believe that the tar paper is the leftovers of the sealant, after years of water and wood staining.

+1 on a FRP backer. Sitkaflex, Lifecaulk, or 4000 will work to seal it up.

I had considered using bronze bolts backwards, using a nut and washer on the outside of the hull...
Would then have to make a 1/4" spacer plate to clear the nut and put a second nut over the zinc. Changing zincs would be easier, and as it ate away, the bolt would not loosen up on the hull. A quick turn of the outer nuts would bite into the zinc. Close trimming of the bolt at the nut would minimize drag.

And then I decided that if I had the boat in ten years, I should worry about it then.

[Richard G.]

Terrific thanks. Bad news is that I just had the boat out of the water and stripped the bottom of 36 years of bottom paint. Would have been nice to have known that it was seeping before relaunching but then…

Next time in about 2 years unless it gets worse.

Thanks again for the feedback.

R

[joemerchant]

Back with StarBoard. Easy to work with and holds up very well. Sold at West Marine. We did all the through hulls last year.

[Ron M.]

If I recall correctly - starboard isn't recommended for backing plates on thru hulls or fittings.....caulk doesn't bond well to it.
In fact I cut 6 backing plates out of the stuff when I replaced all of them a few years ago - but didn't install them.
Went with FRP.

[ch.ocallaghan]

When I bought my 25D, the backing board for the ground plate was similarly in bad shape, decayed and leaking.

I scraped everything off, used a grinder to get down to clean fiberglass, sealed the old holes with filled epoxy, and used a piece of GPO-3 fiberglass sheet as a new backing board, epoxied to the hull. I then drilled holes for the new ground plate through the hull and the new fiberglass backer and threaded them to match the new bolts.

I assembled everything together with a drop or two of 4200 in the bolt holes.

I doubt that it will leak again while I own the boat.

See Maine Sails tutorials on fiberglass backers for Thru-Hulls for details.

[tjr818]

Beautiful work. Nicely done, . . . are this Stainless Steel Bolts? I have been under the impression that SS does not conduct electricity very well.

[ch.ocallaghan]

Thanks.

The ground plate is a GUEST Dynaplate made of sintered bronze. The bolts are 1-3" gold plated bolt & nut and 1-3" bronze bolt & nut plus assorted copper washers.

[tjr818]

That should do the trick. Once again, very well done, and thanks for the info about the Guest Dynaplate.

[Northoceanbeach]

I've read my cd28 has a lightning ground plate. That's what you are talking about right? I haven't found mine yet. Where is it?

[Ron M.]

if you have one it would be on the exterior keel. On most CD's it is located approx. amidships about 16" above keel bottom and bolts thru the hull
into the bilge area.
Look at your chainplates, bow and stern stay plates, for #8 or 10 wire bonded to a bolt. Sometimes seacocks are bonded similarly.
These wires, (if they exist on your boat) terminate on the bolts of the grounding plate (Dynaplate) in the bilge.