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Old 07-07-2010, 23:40   #1
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Two-Inch Cockpit Drain Check-Valves ?

When we haul out for various below waterline tasks in a few months we are also planning to "fix" the stock cockpit drains. Currently we have two 1"+ ID drains that empty under the DWL. The drains are too small for comfort and drain quite slowly. Two 2" drains would probably be more like what should have been installed from the start. I would also much rather have them empty out above the waterline to get rid of two holes in the bottom of the boat.

When really heeled over we will sometimes get water in the cockpit through the current drains. If the drains have a shorter run and larger diameter the backflow would be more significant so I'm thinking about putting in check-valves. I'm wondering what the pros and cons of such check-valves would be and where to go shopping for them if we decide to go that way ?

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Old 08-07-2010, 00:34   #2
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Some people cross the cockpit scupper drain lines to overcome this.
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Old 08-07-2010, 01:26   #3
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Anything that creates a restriction in the cockpit drain is bad. So no check valve. You may be overloaded: move some junk to the shore or forward. Maybe ease the mainsheet :-)

Crossing them as mentioned above is sometimes a solution.
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Old 08-07-2010, 01:38   #4
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While you may be overloaded, I've done it when lightly loaded. I think the "really heeled over" part is likey a big contributor. BTW, Nice boat.
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Old 08-07-2010, 05:14   #5
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Unfortunately, contralateral (crossed) drains donít drain very well when heeled.
Do NOT use a check valve!
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Old 08-07-2010, 05:55   #6
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Unfortunately, contralateral (crossed) drains donít drain very well when heeled.
Do NOT use a check valve!
Mine are contralateral (thanks for the word, Gord). never had a problem at all. Seldom get water in the cockpit when heeled.
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Old 08-07-2010, 07:55   #7
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Ok, no check-valves. I thought that might be the right answer both from a KISS and flow-restriction point of view. Now that the Internet has spoken I know what not to do.

I had to Google Gord's word to see if he just made it up or if it is commonly used. The first hit, from MedicineNet.com , was "The contralateral breast is the breast on the other breast". The word made more sense before I looked it up and now I wonder about Gord's reading habits and possible fetishes

Thanks !

(and thanks to Minggat, we like her too)



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Old 08-07-2010, 09:43   #8
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... I had to Google Gord's word to see if he just made it up or if it is commonly used ...
It’s not as commonly used in this marine application, as it’s antonym “ipsilateral” (drain & thru-hull on same side).
I’m a bibliophage, with diversdiverse interests.
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Old 08-07-2010, 09:47   #9
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Crossed cockpit drains require a good bit of thought from an engineering stand point. Some boats easily tolerate this feature and it works well, while others don't drain when heeled over.

Hull shape and cockpit sole location within the section are the key mitigating factors. Built down hulls like the old CCA style boats can have crossed drains with ease. The hull has enough depth at the forward end of the cockpit (usual placement) to permit a substantial angle for the leeward drain line to still dump it's contents. Canoe body hull forms have a much more difficult time with this as they run out of hull depth and have to use shallower angles.

A simple scale sketch of the section will reveal the issues. Just heel the section over and check the drain angle in relation to the thru hull.

Check valves are a no-no as has been mentioned. If you have room, consider draining aft, instead of laterally (crossed or other wise).

One of the calculations I perform when working on an off shore design, is how fast will the cockpit drain. Calculate the volume of the cockpit if filed and how quickly a couple of drains can empty it. I usually shoot for under a minute. You'd be surprised how many cockpits, even with a pair of 2" drains can't empty in a minute. A minute in a swamped cockpit with breaking seas all around is an eternity.
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Old 08-07-2010, 09:59   #10
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... One of the calculations I perform when working on an off shore design, is how fast will the cockpit drain. Calculate the volume of the cockpit if filed and how quickly a couple of drains can empty it. I usually shoot for under a minute. You'd be surprised how many cockpits, even with a pair of 2" drains can't empty in a minute. A minute in a swamped cockpit with breaking seas all around is an eternity.
Excerpted from ABYC H-4 ~ Cockpits and Scuppers:

4.5.9.1
When filled with water to the fixed sill height, and with weathertight hatches sealed to the height of the sill, 75% of the cockpit water volume shall drain in 90 seconds. There shall be no leakage to the hull interior during the test.

See also ➥ Are you pleased with your cockpit drains?
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Old 08-07-2010, 20:13   #11
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Yes, I'm familiar with 4.5.9.1 also 4.5.9.5, 4.5.9.6 and 4.5.10.2, etc. (H-4), But 90 seconds is longer then an eternity, when winds are force 7 and building with breakers coming over your shoulder. The ABYC recommendations are a lovely thing, but often I find I have practical contentions with some elements of them.
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Old 08-07-2010, 20:39   #12
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IMHO

PAR is spelling out how ideally things should drain out. Great stuff.

There are 2 things going on here. But thay are being lumped together and not getting clarified. Water coming in from scuppers that are below the waterline, and water that needs to drain, wherever it came from. If breasted on breasted lines... sorry, contralateral, then that should help minimize or eliminate water coming in from below. But, depending upon angles ect, it may not allow water to drain out so easily.

So if you take on water from being pooped, or for any other reason, how likely are you to be heeled over at the time.

Just my thoughts. (Not the ones about breast on breast)
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Old 08-07-2010, 20:56   #13
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There shall be no leakage to the hull interior during the test.
That is another concern I have been mulling over. I think I may actually have brought it up here on CF a while back, but it might have been on another forum.

Our engine instrument panel is down in the cockpit footwell and I am sure it would leak like a sieve. There were also old autopilot panels and vent holes that we glassed over, but the instrument panel is still something to think about.



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Old 08-07-2010, 21:00   #14
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The previous owner of Espina decided he wanted honking big drains, so put in two drains made of 5x3 channel running from the cockpit bulkhead aft out the transom. As long as she is balanced on the water line I don't usually get water coming in anymore but the first year was a hoot. I had a foot of water in the cockpit at times because she was trimmed stern down. Now shes still a bit stern low with two in the cockpit and I need shift more ballast forward so she is level with two. To keep the water out I use a couple of plugs that tap in from the inside, with loops on them so they can be yanked out in a hurry.





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Old 08-07-2010, 21:09   #15
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We (for silly reasons not to be discussed) have two steel boats. A Murray 33 with an aft cockpit and a 44' Pape center cockpit. Both have 2 - 2-inch cockpit drains straight down through the hull. Both boats are about 1985 vintage.

One of the things I don't like about the drains is that I can't think of a good way to maintain them. How the hell do you get in there and clean them up and give em a good coating? So I have been thinking of doing something different.

On the Murray, aft cockpit, I could fairly easily reroute the lines out the stern. Replacing the steel (2" galvanized conduit?) with muffler hose out the transom or out the side. I would then weld up the existing openings. It would be a PITA but so be it.

On the Pape it is a much bigger deal as the bottom of the cockpit is low chest high. I can't figure any good way to do it. And of course the drains are all covered up behind furniture. #$%^.

While I probably speak blasphemy, I had thought of simply ridding myself of the drains or putting in a sump with an electric pump and manual back up. The cockpit is not that big to start with and the chances of her filling with water are pretty small considering the freeboard.

This is one of those things that I worry about at odd times when all else in my life is quite and I need some entertainment save I become peaceful. Not much danger of anything happening very quickly.
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