Fixing Water Intrusion

Posted: November 1, 2012

By: Frank Lanier

The drain-plug fitting for my boat is coated with 5200, which I believe has been compromised over the years. It looks as though there is a layer of wood beneath the glass, and I’m concerned there could be some saturation problems, as I’ve noticed water dripping out for hours or days after I pull the plug. Any ideas/suggestions on what I should do?
Small-boat transoms are typically of cored construction, meaning you’ve got an inner and outer skin of fiberglass with some material sandwiched/bonded between them (usually marine plywood). The primary concern with cored construction is preventing moisture from entering the core and causing trouble — wet wood coring can rot, causing delamination and drastically reducing structural integrity. The number-one cause of water intrusion into a cored area is drilling and mounting equipment and hardware (such as a drain plug) without properly sealing the exposed edges of the coring against moisture entry.

If you believe the caulking has failed and there may be water intrusion into the coring, you’ll want to remove the drain-plug tube (the part mounted into the transom that accepts the plug) so you can inspect the condition of the coring.

To do this, remove the mounting screws, pull the tube, then clear away any residual caulking. Since 5200 is a very strong adhesive — depending on the strength of the bond — you may need to use a product such as Debond ( to avoid damaging the drain tube or gelcoat.

Once the drain-plug tube is removed, you should be able to see the edge of the coring. Use a flat-blade screwdriver to probe the coring. If it is dry and solid, seal any raw edges with epoxy (to prevent future water entry), let dry and then reinstall the tube using plenty of caulking.

If the coring is damp but in otherwise good condition (e.g., firm with no delamination from the fiberglass skin), allow it to dry before sealing and reinstalling the drain-plug tube.

If the coring is saturated and/or deteriorated, it will have to be replaced. At this point, you’ll want to have the transom evaluated by a marine surveyor or repair facility to determine the extent of the damage.

Finally, don’t forget that screw holes can also let in moisture. Most boaters simply squirt some sealant under the screw head during installation, but a better method is to drill the screw hole slightly larger than the screw, then fill the hole with thickened epoxy paste. This allows you to then drill the screw pilot hole into solid epoxy, reducing the chance of water migrating into the core.