Inflatable Boat Drain Scupper with Non-Return Valve (Ø40mm)

This drain kit with non-return valve is designed to keep your inflatable boat’s interior dry by automatically expelling any water that enters. It requires a 4 cm (40mm) cut-out for installation, a common size for transom drain holes on many RIBs and inflatable boats. The design consists of a plastic body with an external rectangular flange (approximately 6 x 5–6 cm) that mounts on the transom with screws, and an internal flap valve section with a rubber gasket.

The core of the scupper is a one-way flap valve – a flexible plate or rubber flap that opens outward to let water out from inside the boat (for example, when you get up to speed, water will automatically drain through the opening). When outside water tries to come back in (such as a wave hitting the transom or when the boat slows down), the flap presses shut, sealing the hole and preventing ingress. This feature is extremely useful in rain or when taking spray – the boat self-bails while underway.

On the exterior side of the transom, the drain has a safety cover/door. This cover can latch closed (for instance, when the boat is stationary or moving slowly, to prevent any backflow). It has a catch mechanism that snaps it securely in place so it won’t accidentally open. When needed, you can also leave the cover open (latched in the open position) to allow continuous draining.

Inside the boat, covering the drain opening, there is an integrated mesh screen that acts as a strainer, catching larger debris – leaves, weeds, or other trash that could clog the flap. This makes maintenance easier, as you just need to periodically clear any buildup off the strainer rather than dig out a clogged valve.

• Installation: Typically involves cutting a 40mm round hole in the transom. The drain is positioned with the flap valve on the inside and the outer frame and cover on the outside. It is secured with several stainless steel screws (often not included). It’s advisable to apply a marine sealant around the flange during installation to ensure a watertight fit.
• Operation: Keep the cover closed when the boat is at rest or heavily loaded, to prevent water from seeping in. When you get underway and the boat is on plane, you can open the cover – any water inside will flow out through the one-way flap. At higher speeds, a suction effect improves the draining efficiency.
• Advantages: Maintains the cockpit and bilge of your inflatable boat in a dry state without manual bailing. This increases comfort and prevents large amounts of water from accumulating, which could affect stability. The non-return mechanism protects against sudden backwash flooding when coming off plane or in following seas.
• Application: Compatible with various inflatable boats and RIBs – many manufacturers include such drains by default or as an optional kit. This model (code 02199-37) is a standard size that can replace or supplement an existing self-bailer on your transom.