How to remove water from a wet fiberglass boat transom

Dave Osmolski


This past year, the brass tube for one of my boat’s self-bailing scuppers came loose. I decided to refasten the brass tube and make it watertight before we left on our annual fall trip to our homemade tropical paradise in Southwest Florida. First, I removed the tube and waited for the transom to dry out. Despite the warm, dry weather, the transom stayed as wet as the day I first removed the tube.

This led me to a discovery: Transoms, rudders and other thick constructions on fiberglass boats are not solid. They are built with air spaces between the laminations primarily for weight reduction.

While my boat never sees freezing weather, many members’ boats do. This got me thinking: If my transom stayed full of water and froze, the expanding ice could do considerable and perhaps irreversible damage. I envisioned the engine falling off the back of the boat along with a hunk of the transom!

I considered buying a small pump and somehow extracting the water using a thin flexible tube working through the laminations. Then I realized I could remove the water using my wet/dry shop vacuum. I plugged the inside of the self-bailing scupper hole as best I could. Then I put the vacuum hose over the outside of the scupper hole and turned on the vacuum. I extracted over two gallons of water from my transom. Several days later, the hole remained dry, and with a bit of 5200 adhesive, I put the brass tube back in place and sealed it up.

Although the above repair worked for my situation, what do you do if there isn’t a convenient hole from which to extract the water?

One solution would be to drill a hole at the lowest point of the rudder, transom or whatever structure is dripping water. Drill just through the first layer of fiberglass and into the laminates. Do not drill all the way through. I suggest using a battery-powered drill to avoid any problems should water come squirting out while you’re using a 120-volt drill.

Drilling a quarter-inch hole should allow all the water to drain out quickly and completely. If you drill at the lowest point of the construction, you may not have to use a vacuum as I did. Let the area dry out over the winter, and in the spring locate the spot where the water originally entered, repair, and seal it. Be sure to repair and seal the drain hole you made as well.

David H. Osmolski of Charlotte Power Squadron/27 has been repairing boats since high school when his first boat, a canvas-covered canoe with cedar ribs, leaked in gallons per minute and required constant repair.

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1 thought on “How to remove water from a wet fiberglass boat transom”

  1. Good start. The shop vac helps enormously. I would use heated air ( hair dryer) before using WATERPROOF epoxy composite used to fill smaller voids if not the original designed voids. A truly waterproof inner structure would set my mind at ease. I have replaced rotted plywood transoms more than once in antique power and sail boats. Keep your motor “On the transom”! West Marine has pics in their free catalogs– how to do it!

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