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Old 11-18-2018, 04:59 AM   #1
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raw water thru valve leave open or close

I have a 34ft mainship trawler with twin yanmars. I flush both emgins with fresh water after use with connection piping. my question is should I leave the main raw water thru valves open or close after I flush.

Leaving them open would be most convenient but I'm thinking closeing them to lock fresh water in the engin would be better for the engins.

Could you give me an opinion

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Old 11-18-2018, 05:32 AM   #2
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If the boat is out of the water in freezing conditions be sure to open them so that any access water will drain out. After they drain I donít think that it matters whether they are open or closed. If the boat will remain in the water under freezing conditions they should remain closed and drained with the plug in the side of the thru hull valve.

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Old 11-18-2018, 07:37 AM   #3
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The fresh water from your engine flush should remain in the engine block, heat exchanger, water pump etc, regardless of if the sea cock is left closed or reopened after flushing. I suppose there's a safety factor of leaving them closed as long as you remember to open them before starting.
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Old 11-18-2018, 08:01 AM   #4
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If the boat is in Marco Island, FL, freezing isn't an issue. If you want to leave the seacocks closed, put a string loop on each engine key, and hang the keys on the seacock levers. As long as you open the seacocks before starting the engines, really don't see any issues with keeping the seacocks closed after flushing.

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Old 11-18-2018, 08:44 AM   #5
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Ha! I didn’t see a Marco Island. Let’s hope it doesn’t freeze.
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Old 11-19-2018, 02:50 PM   #6
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For safety, if the seacocks are open and a hose fails while the boat is unattended, there is a higher chance of the boat sinking. I used to close my seacocks anytime I left the boat for more than 24 hours. I've gotten lazy over the years.
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Old 11-19-2018, 02:56 PM   #7
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Since we are usually away from our boat for 3-4 week stretches we always close the thru hulls when we will be away. Leave a note at the helm - all thru hulls closed - and a big red not ready for flight tag on the wheel. I just open them first thing as soon as we return to the boat. Feels safer with them closed while we are away.

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