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Old 09-11-2012, 18:25   #1
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Cockpit Drains

I can't tell you how many books and articles I've read where this phrase is mentioned: "... hope we don't get another wave over the stern, the cockpit hasn't drained yet."
The cockpit is usually the largest water catchment area on the boat. On many boats, if the water gets to deep it simply drains into the cabin. ... OOPS ... To alleviate this possiblity I've increased the drain size on my boat as well as moving them to the corner instead of 8 inches from the corner.
Three inch, 1/2 inch thick, fiberglass tubes glassed to a single 4 inch outlet with 6 layers alternating 2 oz mat & 10 oz roving fiberglass. It was an interesting and difficult project to install because of it's location.
I've calculated that a completely topped of cockpit will drain in 30 seconds. If the waves come faster than that I'm in trouble anyway.
The center is finished. I still have to glass the tubes to the cockpit corners. Tomorrows project. It should be easier because I don't have to crawl underneath the cockpit with wet glass.
The ideas are from Hal Roth and his Spencer 35, Whisper.
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Old 09-11-2012, 19:03   #2
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Re: Cockpit Drains

Hmm... I have two 1.5 inch outlets. Cockpit has about a four foot by seven by two volume between the seats, the stern, and the bridgedeck. Dunno how fast that would drain.

OTOH, I don't think any would get into the cabin ... in any circumstance in which a boarding wave was possible, I'd have the companionway boards in. If the wave was sufficiently powerful that it broke the boards, I'd be screwed anyway, I think.

Interesting project, though.

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Old 09-11-2012, 19:18   #3
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Re: Cockpit Drains

Nice work.. It would be interesting to test your 30 second theory, by blocking the drains and filling it. Just to be certain ;-)
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Old 09-11-2012, 19:32   #4
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Re: Cockpit Drains

Quote:
Originally Posted by Connemara View Post
Hmm... I have two 1.5 inch outlets. Cockpit has about a four foot by seven by two volume between the seats, the stern, and the bridgedeck. Dunno how fast that would drain.

OTOH, I don't think any would get into the cabin ... in any circumstance in which a boarding wave was possible, I'd have the companionway boards in. If the wave was sufficiently powerful that it broke the boards, I'd be screwed anyway, I think.

Interesting project, though.

Connemara

According to my calculations: 3.13 minutes ... of course that just rough
http://www.freecalc.com/drain.htm
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Old 09-11-2012, 19:45   #5
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Re: Cockpit Drains

Originally our boat (36-ft 1978 ex One-ton racer) only had two 1-1/2" cockpit drains. The drains were mounted down in a scupper that went around the floor of the cockpit.

I left the 1-1/2" drains in place as they were the lowest point in the cockpit. I installed two 2" drains on the floor of the forward cockpit and tee'd the 1-1/2" hoses into them. The 2" drains have full flow ball valves.

Works great, completely drains the cocpit with either a little or lot of water in it. The 2" drains go straight down so they can easily be cleaned out with a deck brush handle or stick.

For our "Cape Horn" drain, I installed a 3" drain on the bottom of the cockpit's back bulkhead. We have a counter transom, so the exit drain is normally out of the water. We have our propane tanks located back there, so any gas leakage can escape overboard through the 3" drain.

We have only had one BIG knock down in 27-years, but it was a dozzy - the masthead went under water and the cockpit was nearly brim full when she righted herself. This was 600 miles offshore of Georgia on a passage down to Puerto Rico.

The drains worked very well, but the cockpit locker seats were not very water tight and we end up with about 40-gallons of water below decks. The two Rule 3600 pumps drained that out very quickly.

What we learned was make sure your cockpit seats really do seal well, and inspect everything that goes under water.

We had a leak detection pressure guage on the propane system and it showed everything was OK. When we dis-connected the tanks from the guage to be taken ashore to be filled, the pressure guage still showed everything was OK - in the green (it should have been in the red!).

After closely examining it, I found that the salt water had entered the case and salt deposits had frozen the pressure spring/needle in place!

You learn something every day.....
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Old 10-11-2012, 21:12   #6
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Re: Cockpit Drains

i found some formula on the net about drains and after that calculation it worked out that i had 50% of the drains i should have for a pit our size. Makes you thoughtful.

For every drain you have to have an extra hole to increase the drainage unless you can use another that is not involved in drainage.
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Old 10-11-2012, 21:51   #7
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Seems the cockpit drains should be ample on any well thought out boat. It is not that ocean water, lake water should come as a surprise to any naval architect.

My 32's have two cockpit drains, but with the design of the boats, I have never seen any spray over the sides. I guess I need to push the weather envelope a bit more. Not enough wind and rain to give the drains a proper test.
When washing the boat, all water exits quickly.

Again, seems odd any sailboat cockpit drain would not keep up.
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Old 10-11-2012, 23:26   #8
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Re: Cockpit Drains

Gary, hate to tell you , but a garden hose washing the cockpit is about 1/1000 of what comes in if a big greenie comes into the cockpit. It may only happen once in a lifetime, but a big wave(or multiples) could be the end of a life. My wife was washed clear out of the cockpit by a knockdown that filled our cockpit. Only a safety harness saved her life. Really big drains are a safety factor. Been there, done that!____Grant.
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Old 10-11-2012, 23:45   #9
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Re: Cockpit Drains

The good news is that most of the water rolls and sloshes out of the cockpit, leaving only about the lower third of the cockpit volume for the drains to handle. At least on our last boat, with somewhat low coamings.

There is humor in the cockpit drains making the big whirlpools and air sucking sound you remember from taking baths as a child.
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Old 11-11-2012, 11:25   #10
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I have an outside built in 100 gallon tub on our bedroom deck. Fun taking an outside bath sometimes. I plumbed the drain in all 4' pipe. That tub drains in a couple seconds.

My sailboat was not built to circumnavigate the globe. For sailboats that are, would seem odd to drain the cockpit with 1" drain tube with several bends in the hose.

My 32 aft cabin has 2 drains, 1 1/2", straight down to thruhulls in the bottom of the sailboat. Had I designed the drains, I would have had them drain above the waterline. One less (2) chance for a hose coming off and sinking the boat.
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Old 11-11-2012, 11:54   #11
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Re: Cockpit Drains

I've always liked the cockpit scuppers that criss-cross on the basis that you are likely to be heeled at the point when you want them to drain.

Someone here recently showed how they had gotten rid of the seacocks and just made them permanent open, but in the "X" format.
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Old 11-11-2012, 13:27   #12
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Quote:
Originally Posted by S/V Alchemy
I've always liked the cockpit scuppers that criss-cross on the basis that you are likely to be heeled at the point when you want them to drain.

Someone here recently showed how they had gotten rid of the seacocks and just made them permanent open, but in the "X" format.
No seacocks if they drain above the waterline is a potential problem how? That seems fine.

If the drain for the cockpit terminates below the waterline, seems to me having no seacock is asking for trouble. A prudent person would close all below water thruhulls whenever the boat is slipped unattended.
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Old 11-11-2012, 13:45   #13
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Re: Cockpit Drains

if you get water coming into your cockpit from your drains I think you have a problem that a valve isn't going to help with

I think the OP action of improving drainage is a good idea, for more reasons that being swamped
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Old 11-11-2012, 13:59   #14
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Re: Cockpit Drains

Plans feature 3 x 3" drains per side, sloped cockpit floor with a grating to stand on. Kneehigh coamings on the hatches, doggable lockerlids of rubber-gasket steel, no connection to cabin. Probably overkill, but I like it. Actually the top of the boat is as strong as the bottom, if not more so.

Funny, I had a dream last night the 6m whaler swamped...on waking, I reviewed the plans for that too, making sure that there's enough built in floatation below the level of the centreboard slot to keep her within bailing distance of the surface. Must remember to figure out a way to seal that slot so bailing isn't a pointless exercise. And yes, the floatation higher up than that is enough to self-right, because it's imbalanced; she is not stable upside down. Still playing with the idea of installing self-bailers, but a bit queasy at the thought of holes. Buckets seem safer to me....
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Old 11-11-2012, 13:59   #15
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Re: Cockpit Drains

Wasn't it Eric and Susan Hiscock who had a canvas liner made for the cockpit, with a pick up handle on the floor so that they could do a quick dump.
There would be many variations on the theme.
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