Water cooled engines on a boat

[sunny marella]

Hi,

Can somone explain to me what this contraption is(Upon querying the boat-man,he replied it had something to do with water cooling the engines).
(//postimage.org/image/4g03vm1bn/),but this "thing" was at the boat aft.Is this some kind of a siphon exit?
Isn't the water input supposed to start at the hull given that it is a open system?(Logically seems correct to me)
Thanks!

 

[brewnog]

Photo doesn't work...

 

[Pkruse]

Can't see the picture, but from your description I'll take a guess that you are talking about the riser in the exhaust manifold. Think about it as an upside-down S-trap in a plumbing drain. Does the same thing in the opposite way. Prevents water flow back into the engine thru the exhaust.

In a raw water cooled system, the water first flows thru the engine water jacket, then thru a jacket on the exhaust manifold, which is probably the thing you are talking about. Some of the water is also dumped into the exhaust flow itself, so you have wet steam exiting with the exhaust at a port near the water line. The riser prevents water to flow into that port and into the engine.

 

[Pkruse]

Another thing to consider is that while raw water cooling used to be very common, it is more common today to use fresh water coolant mixed with antifreeze, just like in your car. The only thing that would be different from what I wrote above concerning the raw water flow would be that it would flow through a liquid-to-liquid heat exchanger instead of the engine water jacket. This heat exchanger would serve the same thing as the radiator in your car. (The term "radiator" is not technically accurate. What you really have in your car is a liquid-to-air heat exchanger. it actually radiates very little. Most the heat transfer is in convection.)

So the thing you are looking at may be a heat exchanger.

 

[marellasunny]

Photo attached.Please verify if this is what it seems.
Unable to post pic as i am a new member.

But the S-Trap explanation fits,although i still can't comprehend this to be a heat-exchanger.(No heat flow was detected at exit).

 

[Danger]

Photo attached.Please verify if this is what it seems.
Unable to post pic as i am a new member.

But the S-Trap explanation fits,although i still can't comprehend this to be a heat-exchanger.(No heat flow was detected at exit).

That appears to be the snorkel of a submarine that is trying to surface directly beneath you...

 

[Pkruse]

That appears to be a vent intended to break a potential siphon in the cooling system. You see the same thing on top of most houses, so that a negative pressure cannot developed in the sewer lines and possibly suck the water out of your S-traps. Also a convenient access port to clear obstructions from the line with a rodder.