How To Install A One-Way Scupper Valve

By Dan Armitage
Published: Fall 2013

If you find your feet getting wet on your boat's self-bailing deck, something's amiss.

Whether it's worn scupper-valve flaps or the weight of a heavier four-stroke outboard (or crew members!) at the transom of your boat submerging the self-bailing drains, if your deck scuppers are allowing your deck to flood when weight is shifted to the transom, or the boat is backing, consider installing an aftermarket scupper system that allows water to flow in only one direction: off the deck and out of the boat.

Photo of the tools need for the scupper valve installation
Photo: Dan Armitage
The tools needed were minimal — a Phillips-head screwdriver and marine-grade sealant.

Several styles of one-way scuppers designed for use on self-bailing decks are available: duckbill, flapper valve, and ball style are most common, for which aftermarket versions are available. The ball style is popular among owners of trailerable boats for their effectiveness and relative simplicity, and we selected T-H Marine Supply's Flow-Max Ball Scupper ($14.99 at for our application. The T-H offers a large exit hole for quick draining, and a twist-off feature makes for easy cleaning when leaves or other debris clog the system. The Flow-Max ( meets all ABYC standards, includes a stainless-steel security pin, multiple mounting holes, and a neutral buoyancy ball that won't float up and break the seal. All one-way scupper valves should be checked regularly for possible debris.

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