Thru Hull Scupper Valve for Bilge Pump

I am building am electric bilge pump for my wilderness systems tsunami 175…the cockpit is huge and I am doing winter paddling.

I am looking for a scupper valve that will go into a 1 inch hole. This valve prevents water from flowing into the cockpit but allows it to be pumped out. There are plenty out there that use a bigger hole and 1 1/2 inch hose, but those are too big for my application.

Right now I am using an inline check valve in the cockpit, but its not as nice as having the check valve right at the kayak hull.

bilge pump
Bilge pumps discharge above the water, often thru the deck on a kayak, there’s no reason to risk flooding the boat if a part fails having the discharge thru the bottom.

Bill H.

Why bother?
The pump itself should keep back flow from entering the boat. A 1" column of water maybe no longer than a foot isn’t enough water to worry about. I’d keep it simple.

Don’t discharge below the waterline.
Bilge pump discharge through-hulls that are located below the waterline sink yachts from time to time. Bad idea. The pump cycling off can start a siphon of water flowing into your bilge. Electric impeller pumps do not prevent backflow the way manual piston or diaphram pumps do. There is no check valve in an impeller pump.

And there’s no advantage to discharging below the waterline. You’ll just add drag. You can get through-hulls in a wide variety of sizes, shapes, and materials from a marine supply store (like the dreaded West Marine). On one of my kayaks the bilgepump discharges just below the sheer stripe next to the foreward bulkhead.

If you’re going to do a lot of rolling or really rough water stuff you might consider adding a joker valve at the through hull to prevent any leaking through the through-hull, but I think you’ll probably get more leakage through your skirt tunnel if you’re in conditions that are that crazy.

Never saw a discharge below waterline

– Last Updated: Nov-14-10 10:01 PM EST –

The thru hull goes in the top of the deck where it discharges. Not sure how anyone imagined I was drilling a hole below waterline (I guess using a thru hull should be called a thru deck).

Anyhow..the cockpit is watertight, and quite a bit of water goes over the top deck in rough water. Thats why I have a skirt. I can't imagine water not getting through the thru hull....

It would be nice if the water stopped at the rubber flapper right at deck level.

Water washing over the deck won’t back flow thru the pump enough to matter. Keep it simple.

Bill H.

No need for the check valve
Simply loop the discharge hose from the pump before you discharge out the valve. Works great and you don’t reduce the output of your pump because of the check valve, which can cut your pump output down fast. Check out my setup at you can see the hose looped below the deck in this video as well.

Loop sounds like good idea.
The loop sounds like a great idea.

I don’t believe that a centrifuge type bilge pump will stop backflow.

centrifugal pumps have little resistance to backflow.

How about mounting a joker valve right inside the thru-hull? Find one the right diameter so it just slips into the thru-hull, and you could silicone or sikaflex it in place. If it wears out, just scrape it out and install a new one. That’ll be simple, low profile, and fully watertight. It also won’t add bulky moving parts to your deck, where they could get tangled with other gear or get broken during a rescue.