open scupper issues

Im looking for comments on how to adequately shield 3"x10" open scuppers from green water penetration, Im thinking of a cast alum. bilster of some sort..

 

I would caution against a fixed modification that would reduce the actual clear open area of the scuppers. A blister or cowl may be difficult to arrange with out having a negative effect on the open area, and may give rise to problems more irritating than the one you have now. That being said, some freeing port "flaps" work very well and can be as simple as hinged plate and some well-placed stops. They work as a flow-check mechanism, opening for outboard-flowing water to pass, and swinging closed against inboard flows. Some arrangements call for the flaps to be held closed with magnets but more commonly gravity and a well thought out installation do well enough. I assume you'd be custom fabricating these, and the job would be a sight easier than casting blister shapes. No source for manufactured flappers comes to mind, but I hope this helps.
-K

 

Thanks for the comments, weve used "flaps", with some success in the past, but as this boat will be run in Alaska, freezing may become an issue. I had hoped there might be a source of custom sized flappers out there somewhere. Thanks again.