Engine cooling water intake thru-hull

[The grouch]

Hi.
I've read and understand the reason for closing the thru-hull for engine cooling water intake while towing.
My question is :
At what water flow speed should you close the valve while anchored in higher water flow areas, like rivers or higher tidal flow areas ?

Thanks
Larry Hart
2011 21ec. Equinox

 

[bob daily]

Larry, this was explained to me a few years ago, basically at 0 knots the water level in your cooling system would be at sea level, with every MPH of water flow it would double. IE at 1 MPH it would be 2 inches above sea level, at 2 MPH it would be 4 in, and at 3 MPH 8 in and so forth. The best rule of thumb is to close the sea valve if in doubt! I heard that a boat was sunk last week at Sekiu,Wa due to a cooling hose connection to the sea valve. Bob

 

[The grouch]

Thank you for the reply Bob .
Will be careful for sure .
Appreciate your info.
Larry
21ec. Equinox
⚓

 

[Ralf H]

Hi the grouch!

bob has it right. When in doubt, ALWAYS close the valve. I'm not sure as to the formula for calculating the rise of water, as bob mentioned, so will take it at face value. However, the best way to know for sure is to close the seacocks. They should all be closed when you are away from the boat for any period of time regardless. Hope this helps.

Cheers,

Ralf

 

[Wee Venture]

Larry, this was explained to me a few years ago, basically at 0 knots the water level in your cooling system would be at sea level, with every MPH of water flow it would double. IE at 1 MPH it would be 2 inches above sea level, at 2 MPH it would be 4 in, and at 3 MPH 8 in and so forth. The best rule of thumb is to close the sea valve if in doubt! I heard that a boat was sunk last week at Sekiu,Wa due to a cooling hose connection to the sea valve. Bob

I’m a little confused about the formula. What are you doubling? If you start with zero inches and double it, of course that is still zero. Do you double the mph to get the number of inches above sea level? In that case, 1 mph would be 2”, 2 mph would be 4”, 3 mph would be 6” and 4 mph would be 8”. I may not be understanding.

Regarding seacocks, I have never heard of anyone having water forced into the engine when anchoring in a current, which makes me suspect there would have to be a pretty strong current to be a problem. On the other hand, I do want to learn about real risks so I am willing to learn.

So many things in life are about balancing risks since you can’t really eliminate them all. E.g., if you anchor in a current, a very real risk is the anchor pulling out or dragging. Then what’s the first thing you’re going to want to do? …start your engine. Are you going to remember in an emergency that you closed the seacock? Do you have time in an emergency to lift the hatch and open it again?

I, for one, do not close the seacocks every time I leave the boat. I do inspect the hoses and clamps every time I do an engine check—which is pretty much every time I start the engine. If I am leaving the boat for an extended period of time, say a week or more, I will close the seacocks and tape a message to the wheel. I have heard people cite boats that have sunk and say you should close the seacocks even if you are just going ashore for dinner. That is undoubtedly the safest (assuming you remember to open them again before you start up!) but I have not done that. Feel free to convince me of the error of my ways.

John

 

[bob daily]

Mr john, sorry if I confused you with my post! This was explained to me by Mr Northern Focus on a thread dated 23-Apr-20, titled (close sea clock prior to being towed) I'm sure my numbers were off, but bottom line is yes you can hydro lock your engine if anchored in a strong current! We fish below the dam where the current can exceed 5-8 knots and I always shut my sea valve. To each his own.
Just stay safe! Bob

 

[Wee Venture]

Bob, wanted to thank you for your reply. The thread that you referenced was very helpful. I don’t think I’ve ever anchored in that much current so maybe that’s why it has never been an issue for me. Another potential problem to watch out for. Boating seems to be full of them! But full of great adventures too!

John