Might be a silly questions but it's more about physics

[Windtherapy]

Cabin cooler drain. I hear that it drains into the bilge area--silliness but, I will change mine to the sink drain as others have suggested and have done. Here is my question, laws of physics apply I believe so I am just curious. The thru-hull for the galley sink drain is at the very bottom of the boat and almost straight down from the sink itself. How does it drain when at rest with the water pressure below the boat at the thru-hull? itself I can understand draining while at sail but not at rest.

 

[Jackdaw]

Like any other thru-hull, it will drain down to the current water line. I assume the bottoms of the sink and box are above the water line, so the contents will drain from them and settle on the waterline somewhere in the hose.

 

[Don S/V ILLusion]

Same principle applies regardless of whether you are under sail or not. Picture pouring more water into the straw in a glass of infinite size (the ocean)

 

[Jackdaw]

Same principle applies regardless of whether you are under sail or not. Picture pouring more water into the straw in a glass of infinite size (the ocean)

Moving water over the thru-hull opening creates low pressure that definitely helps suck water out.

Watch how much more quickly your sink drains while underway.

 

[Don S/V ILLusion]

Moving water over the thru-hull opening creates low pressure that definitely helps suck water out.

Watch how much more quickly your sink drains while underway.

Haven't done the math but at 5 knots, I doubt the pressure differential is observable. However, you are correct on the theory.

 

[Capt jgw]

Exactly. If you put stinky stuff down the drain, it will stay in the hose until more water is drained through. Eventually you will smell it in the boat. So flush more water down if you do that.

 

[centerline]

Haven't done the math but at 5 knots, I doubt the pressure differential is observable. However, you are correct on the theory.

This would depend on how the thru hull is faired to the hull and/or the angle that it intersects the flow of water past it..there is just a couple of degrees of angle difference between it being either a minus pressure to help suck the water down the drain or a positive pressure that could keep it from draining...
At a speed of 5kts, it could be a substantial difference.

 

[Don S/V ILLusion]

This would depend on how the thru hull is faired to the hull and/or the angle that it intersects the flow of water past it..there is just a couple of degrees of angle difference between it being either a minus pressure to help suck the water down the drain or a positive pressure that could keep it from draining...
At a speed of 5kts, it could be a substantial difference.

This quickly gets into an academic exercise but I'll 'bite'.

As its all about pressure differential, intuitive answers don't usually stand up to scrutiny.

Can you define how angle affects pressure differential and what differential would be expected assuming laminar flow past the thruhull?

I am a chemical engineer so I might be able to understand the math.