Scupper Worries

[Jim Cooper]

My center console fishing boat has the 6" oval transom scuppers with the hinged flapper door on the exterior side (PVC plastic). If backing down or facing aft in a following sea the flapper door is pushed upward, allowing a surprising amount of water to fill the cockpit. I've thought about weighing the flapper door down somehow but I think the amount needed to counter the rush of water would be prohibitive. The flapper door is top-hinged.
Anyone have an idea how to negate the flapper door from being pushed upward when outside sea water flows toward the transom?

 

[Bmarler]

You might attach a limiter to the scupper to keep it from opening more than 45 or 50 degrees. Either a lanyard from the bottom or a stopper on the hinge.
If you limit the swing it will slam shut when you back down.

 

[remwines]

A picture could be helpful. I also have a fishing boat with transom scuppers, but they can be sealed off with standard bilge drain plugs from inside. 6" oval is a big hole. Perhaps you can install a SS tab/bracket like Bmarler suggested over the outside of the flapper to limit travel so when hit by surge it would be mostly closed. Another thought would be installing a SS corner bracket on the outside with a small weight (trimmed zinc anode) to hold the scupper closed until water from inside the boat pushes it open. The flapper would also tend to be more open when you are underway and the bow is up.

 

[Nautica]

I'd try it with a small weight (anode) bolted to the flap first. It doesn't need to counter the weight of water, just hold it near closed at first, then the weight of water will push it closed instead of open. There are many flaps with weight attached. And yes, picture would help in case we've got it wrong.