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What Are Scuppers on a Boat? (Types, Funtion & More)

Written by J. Harvey / Fact checked by S. Numbers

what are scuppers on a boat

When it comes to managing water that gets onto the vessel, it is the bilge pump and scuppers that keep things manageable. But what are scuppers on a boat, and how do they help keep us afloat?

A scupper is an opening on the boat walls where water can go through and exit the vessel. However, there is more to learn aside from the scupper meaning. Let’s take a look at other essential information about them.

Boat Scuppers and Their Function

It is not unusual for water to get into a boat; there’s rain, overspray, or even small leaks, but thanks to the scupper, these won’t pose a big threat to the vessel.

The basic scupper definition is simply an opening where water can pass through. On a boat, this component can be found in the divisions or bulwarks of the vessel. On a scupper ship, however, the water may be redirected to the gunwale, where it may then exit through the side.

Types of Boat Scuppers

1. Simple scuppers


This is simply a scupper hole through which water may exit the boat. Those found on a kayak commonly make use of plugs to seal them.

There are also the boat self bailing scuppers, which are ideal for smaller vessels. These self bailing boat scuppers allow water to exist from the vessel without the need to unseal them manually.

2. Flap-sealing

This type uses a rubber flap that moves in a single direction to allow water to drain from inside the vessel. Any force from outside will not open the flap, which makes it an effective seal to keep water out.

3. Stainless steel boat scuppers



This type uses a tube that bends 45 degrees in the middle to prevent water from getting onto the deck. It also features a stainless steel flap, which only opens when onboard liquid needs to pass through, for further protection against water entering from outside.

There may also be a filter in the boat drain scupper to keep small debris out. As this type of scupper is made from stainless steel, it’s rust-resistant.

4. Ball-lock type

It uses a ball lock that moves depending on the water pressure. When there is water on board, it forces the ball away from the opening to allow it to flow out. Water from the outside forces the ball into place, making for an effective seal.

5. Duckbill


This scupper type functions in a similar way to others but makes use of a duckbill-shaped seal instead. It has a thermoplastic flap that opens like a mouth when water needs to exit from the vessel.

Water from outside does not open this scupper because its unique shape keeps it closed when exposed to outside pressure.

How Does It Work?


Scupper drains for boats mostly work in the same way—they are essentially outlets that go through the hull to allow the water to exit from the vessel.

When you open the flap of deck scuppers on ship, the water onboard will pass through the tube and exit via the valve at the end. Valve placement is very important in proper boat scupper installation to ensure that water and debris do not enter from outside.

Scuppers usually feature some sort of one-way valve. These allow water from inside to pass through, while pressure from outside will seal the flap shut. 

Another very significant part of how scuppers work is that the valve is kept above the waterline. If the vessel is left with the boat scuppers below waterline, you may come back to find that water has scuppered the engines or, worse, that the boat has sunk.

Frequently Asked Questions

Do all boats have scuppers?

No, but it is something that boats with decks above the waterline need. On the other hand, smaller boats, especially ones with lower decks, may not have scuppers.

Does a boat scupper have to seal?

Having to seal is not mandatory if the water on board is drained effectively. However, it’d still be helpful to get a plug for your scupper valve boat to make sure nothing bad happens. For instance, the one-way valve may malfunction, letting outside water in.

What is the best material for a scupper to be made from?

A material that resists corrosion is a given but combined with being durable will make it well-suited as a scupper material. Stainless steel and thermoplastic composite are the best ones in this regard.

Plastic and rubber are also good against corrosion but may wear out more quickly compared to the other two.


What are scuppers on a boat? Now you know more than enough about this and a bit of what it takes to keep them in good working condition. These are equipment that keeps our boats safe even when we are away, so it’s good to know about them.

What other safety mechanisms for boats do you know about? Tell us about them in the comments section below

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