Transom through hull fittings

I have a early 80?s Hydro-Sports CC I am fixing up. It has not been in the water for over 4 years. I am replacing the through hull fitting for the wash down pump and bait tank. I took the old one out and there is some water (damp) in between the space in the transom where the fitting was. A small amount of the wood around the hole is rotting (size of the tip of my little finger). My question is: is there anything I should do to try and dry it out before replacing the through hull fitting? I was thinking of putting foam in there or something. I don?t see any way to dry it out 100%.

Second question is there is a corroding metal plate on the outside (by the drain plug) with a long screw going through the transom and a green wire attached to the inside of the hull. The plate is corroded green. Is this some sort of corrosion prevention or ground? If so where should that green wire go to is it a ground?

Thanks for any help

Re: Transom through hull fittings

First, the transom thru hull fittings: Apparently the old seal failed and water was getting into the wood of the transom. So you have the rot you found. I would gouge out as much of the rotten wood as possible without cutting the fiberglass. Sometimes is easy to make custom tools for this like bending cheap screw drivers in a vice to get into the space easier.

After cleaning out the rotted wood, and letting the rest dry, the next step is to fill in the missing wood. This is easily done with some polyester resin and thickener. Mix the resin and thickener (wood flour, cabosil, baking flour, can all be used to thicken resin to a paste consistency) and fill in the missing wood. Might take two or three applications. Then sand and install the new fitting using a good marine sealer like 3M 4200. Epoxy resin can be used too, but for a small repair, the expense of epoxy is prohibitive.

Do a search on these forums for making "peanut butter" or "thickeners". There is lots of info here on how to prepare the materials needed to make this repair. I just outlined the steps needed, details can be found in the forums.

Second, the metal plate with the ground wire is a sacrificial anode. Someone with more experience than me can steer you in the right direction with the anode.

Re: Transom through hull fittings

scuba4me said:

Second question is there is a corroding metal plate on the outside (by the drain plug) with a long screw going through the transom and a green wire attached to the inside of the hull. The plate is corroded green. Is this some sort of corrosion prevention or ground? If so where should that green wire go to is it a ground?

Thanks for any help

Click to expand...

Sounds like a bonding/ grounding plate. The plate is used as a ground an onbaord boding system or as a ground for side band, Loran or ham radio installations. If it's unhooked, it's probably not needed anymore and can be removed.

Re: Transom through hull fittings

Mark42 said:

First, the transom thru hull fittings: Apparently the old seal failed and water was getting into the wood of the transom. So you have the rot you found. I would gouge out as much of the rotten wood as possible without cutting the fiberglass. Sometimes is easy to make custom tools for this like bending cheap screw drivers in a vice to get into the space easier.

After cleaning out the rotted wood, and letting the rest dry, the next step is to fill in the missing wood. This is easily done with some polyester resin and thickener. Mix the resin and thickener (wood flour, cabosil, baking flour, can all be used to thicken resin to a paste consistency) and fill in the missing wood. Might take two or three applications. Then sand and install the new fitting using a good marine sealer like 3M 4200. Epoxy resin can be used too, but for a small repair, the expense of epoxy is prohibitive.

Do a search on these forums for making "peanut butter" or "thickeners". There is lots of info here on how to prepare the materials needed to make this repair. I just outlined the steps needed, details can be found in the forums.

Second, the metal plate with the ground wire is a sacrificial anode. Someone with more experience than me can steer you in the right direction with the anode.

Click to expand...

Great info thanks. Peanut butter epoxy might be good to just fill in the gap where the hole goes through. There appears to be an air gap between the outside and inside layer of the lower transom/hull. It appears to be made that way Glass|wood|1/2" gap of airspace|glass. The hole for the through hull is down at the very bottom by the drain plug where the dead rise is, and this aria is offset in from the transom towards the bow about 6". I suspect this gap is throughout the boat and is filled with foam in most arias but not sure.

I think your both right about the anode I just wonder if it should be connected to something or if it really helps anything if I did. I will probably just remove it and fill in the hole unless anyone else has some input as to its need.

Re: Transom through hull fittings

I would not put foam in any area that has structural properties. Especially, an area that is exposed to water on both sides. Foam only absorbs water and creates more rot. Good luck!

Re: Transom through hull fittings

I would keep the "grounding plate" because (1) to remove it just creates another hole or two in your transom which needs to be filled and it (2) it may prove useful to you for its original purpose: to protect your marine electronics as per the manufacturers directions. For example, this is what Raymarine recommends:

"Grounding
The following requirements apply when grounding Raymarine
equipment:
? Use a dedicated earthing plate (e.g. dynaplate) in contact with
the water.
? Ground cables may be routed to a common point (e.g. within the
switch panel. With a single (appropriately rated) copper braid
connecting to the earthing plate.
? Use flat tinned copper braid, 30 A rating (1/4 inch) or greater.
Equivalent stranded wire diameter 4 mm or greater.
? Keep the length of the earth braid as short as possible."

That sounds like Greek to me, but it is really quite simple once your figure it out. The green wire that is connected to the plate would normally be run forward to the helm area where it would be attached to a bus bar or some similar arrangement. The bus bar then serves as the connection for the various "drain wires" (braided sheathing) which surround the power cables furnished with modern marine electronics.

Re: Transom through hull fittings

There is stuff called "Git-Rot". Its for putting in wood that is rotted to make it structural again.

Its not to expensive and its easy to put in. It works great, I have some in my transom.