One way Drain valve at back of boat?

[eve1]

My little boat has this plug hole thing at the stern, not sure what name is in English but the French Vender called it a Bouchon.
I thought thats clever how it works as a one way valve to drain any water, except it doesn't. If I poor water in the boat it doesn't drain out.
Is it supposed to be turned, its stuck but looks like it should turn??

 

[Rocksteadee]

That is commonly known a bung.
It is a plug and it is unscrewed to drain water, provided the outlet is above the water line

 

[BruceK]

That's a bung. On the other side is a flapper valve. When the boat is in motion the vacuum on the back of the transom opens the flapper valve and the water drains out. Water cant easily get back in through the flapper valve but when stationary it does, hence the bung.

Please do not take my word as gospel and remove that bung while in the water until you are absolutely sure that not only do you have a flapper valve on the external transom but that it is in good order.

this is what the flapper valve will most likely look like

or

 

[eve1]

so, if the bung stops water ;leaving, if it rains (say over winter) when Im not there , then it will fill up with water?

 

[Boathook]

so, if the bung stops water ;leaving, if it rains (say over winter) when Im not there , then it will fill up with water?

Yes it will. If the bung hole is above the waterline at rest leave the bung out and water should drain away. You don't say what type of small boat plus another picture of the general area would help as well.

 

[eve1]

Its a 4.2 m french boat with small cabin. The drain hole looks level with or just below the waterline which doesnt seem logical! Its kept in a port mooring.

 

[Rocksteadee]

That looks like it may be a self buoyant boat.
you could try taking the bung out whilst floating and see how much it fills with water, then you are confident that it can be left out to allow rain to drain out.
Only do this if you have a bucket handy or a bilge pump and confident that the bung can be screwed back in. Ideally whilst just floating on a slip

 

[BruceK]

If it has a flapper valve as I suspect then yes it needs to be below the waterline

 

[eve1]

so what I dont understand is if it does have a flipper valve why bung it off from the inside?

 

[Rocksteadee]

Le

so what I dont understand is if it does have a flipper valve why bung it off from the inside?

Leave it for long enough and a flapper valve will seep enough water to sink a boat

 

[Davy_S]

I think that it is a simple bung, the deck is not self draining, if it was, it would not have a bung, when you stand in the boat and pull out the plug, water will come in, when you set off under power, the water will drain out, lots of small fishing boats have these fitted, you can swill the decks clean as long as you are motoring forward.

 

[Refueler]

so what I dont understand is if it does have a flipper valve why bung it off from the inside?

Flapper valves only close with positive pressure against them and are notoriously unreliable.

Personally I would not rely on it and would fit something like I have in my ex Soviet boat. I have a small float switch bilge pump ... 12V 7A/Hr SLA battery and a 10W solar panel ... no regulator or fancy bits needed.
Pump sits in the bilge, pipe overboard ... solar panel keeps battery charged ... float switch switches pump on / off as needed.

Using something like that - basically can ignore the flapper / bung affair ...

 

[stelican]

That looks like it may be a self buoyant boat.
you could try taking the bung out whilst floating and see how much it fills with water, then you are confident that it can be left out to allow rain to drain out.
Only do this if you have a bucket handy or a bilge pump and confident that the bung can be screwed back in. Ideally whilst just floating on a slip

DON'T DROP THE BUNG

 

[Refueler]

What's a Self Buoyant Boat ? Thought all boats that float are self-buoyant ?

Think that should read "Self Bailing" or "draining" ?

 

[Rocksteadee]

DON'T DROP THE BUNG

Looks like it is on the inside. Good point though

 

[Rocksteadee]

What's a Self Buoyant Boat ? Thought all boats that float are self-buoyant ?

Think that should read "Self Bailing" or "draining" ?

Self buoyant. Can be completely full up but will still not sink. I think the phrase was originally coined with the mirror dinghy. My dad built one and just to prove it we tried to sink it. Had to have 2 adults and 2 kids in it to get it to go below the surface. We stepped out and the boat floated.

 

[Refueler]

Self buoyant. Can be completely full up but will still not sink. I think the phrase was originally coined with the mirror dinghy. My dad built one and just to prove it we tried to sink it. Had to have 2 adults and 2 kids in it to get it to go below the surface. We stepped out and the boat floated.

Never heard that term ... the one I heard for dinghy's and including Etap :

Unsinkable.

 

[Rocksteadee]

Never heard that term ... the one I heard for dinghy's and including Etap :

Unsinkable.

You could be right as I am remembering back 55 years ago. Same difference. Having enough sealed compartments to overcome displacement

 

[Rappey]

Since it's a small boat that's easy trailorable surely it's just a drain to empty the boat before towing ?

 

[BruceK]

Since it's a small boat that's easy trailorable surely it's just a drain to empty the boat before towing ?

The give away is it's on the inside of the boat. Self bailers usually have the valve on the outside of the boat, whichever type of valve it is. Elephant trunk, ping-pong ball or Flapper Valve. As the transom moves through the water it creates a vacuum that opens the valve. As soon as the boat stops the vacuum stops and the valve closes under the water pressure returning.

As for there being no valve and the bung just removable once underway to drain water, no go. I've tried that plenty times in the tender and it doesn't work.