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Old 20-04-2016, 14:34   #1
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Self-Draining Cockpits For Small Boats

Ideally, we'd all have cockpit soles well above WL, but this is often impossible on a small boat, if we're going to maintain sufficient cockpit depth. Boats with soles below WL have no choice but to put their drain outlets below WL. Boats with soles just barely above WL have to choose between a below WL outlet, or a just barely above WL outlet that's vulnerable to backflow in heavy seas.

Here's my solution: (a) Reduce the diameter of the normal, sole-level drains, to reduce the risk of backflow or thru-hull failure; (b) Make up for lost drainage capacity by adding larger drains well above sole level, so that their outlet is well above the waterline.

Like this:



Because the flooding risk associated with drains 1' above WL (for instance) is so much less than for a drain at or below WL, one could make these upper drains much larger in diameter than the typical sole level drains: allowing for extremely rapid drainage of a cockpit full of water. This comes at the expense of slower draining when there's just a little water in the cockpit (when only the reduced-size bottom drains are working), but that's a good trade-off IMO. when you most need fast drainage is when the cockpit is most full of water.

Has anyone seen a set-up like this?

P.S. You can use this calculator to get an idea of the size drains you would need to drain your cockpit, at different levels of water in the cockpit. Since the relationship between diameter and area of a circle is not proportional, you'd be surprised at how much more quickly you can drain a cockpit with just a slight increase in drain diameter.
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Old 20-04-2016, 18:57   #2
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Re: Self-Draining Cockpits For Small Boats

Which cruising boats don't have self draining cockpits? I know there is a Cape Dory day sailer that doesn't but I have never heard of this as an actual problem for any mass produced cruising boat.
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Old 20-04-2016, 22:11   #3
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Re: Self-Draining Cockpits For Small Boats

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Originally Posted by vjm View Post
Which cruising boats don't have self draining cockpits? I know there is a Cape Dory day sailer that doesn't but I have never heard of this as an actual problem for any mass produced cruising boat.
I couldn't tell you which designs, but some people certainly drain their cockpits below WL, even into the bilge (!), which would appear (to me at least) to be quite insane if you had the option of draining above WL (thus I assume they don't?).

In any event, there's no such thing as a drain too high above WL.

So perhaps the concept in the OP could be of use.
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Old 21-04-2016, 16:27   #4
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Re: Self-Draining Cockpits For Small Boats

I've seen a couple of small sailboats (about the size of a Laser) that just gave up and have big holes at the transom allowing the water to freely enter and leave the cockpit. Probably due to how much comes over the side at times.

It partly depends on how the boat will be operated. The Vagabond I just got will have a very wet cockpit if pushed to the edge of flipping, especially in rougher water.
But I may be looking for a one-way valve to restrict backflow into the cockpit, while allowing it to drain, since I don't plan to push it that hard.

Or I can keep the tiny footwell of my Minifish dry.,. except for what backs up through the drain. (but that's no fun...)

Neither of those boats would be bothered that much if the drain plugs are left in and the cockpits filled. (as high as the daggerboard hole allowed it to stay filled for the Vagabond) But we kind of like to let our feet dry occasionally.

Sure, for some purposes the small drains at the lowest possible level plus larger holes higher would be just fine.

Tiny drain holes clog easily...
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Old 21-04-2016, 16:38   #5
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Re: Self-Draining Cockpits For Small Boats

If the cockpit sole is below the waterline you'll need to bring a bailing bucket along. That's about it, unless you are going fast enough and then you can open a plug in the transom and let the water get sucked out. Put the plug back in before you slow down!
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Old 21-04-2016, 16:58   #6
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Re: Self-Draining Cockpits For Small Boats

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If the cockpit sole is below the waterline you'll need to bring a bailing bucket along. That's about it, unless you are going fast enough and then you can open a plug in the transom and let the water get sucked out. Put the plug back in before you slow down!
If the cockpit sole is below the w/l, and there are drains, I believe tht the cockpit will fill up to the w/l level... all the time! Bailing would not make much progress unless the drains were very small indeed.

Would make a self-tending aquarium for those with that interest...

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Old 21-04-2016, 16:59   #7
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Re: Self-Draining Cockpits For Small Boats

If the drains are near the stern you have to watch out for the sternwave lifting the waterline and flooding even a cockpit that is normally well above sea level at rest. Thats why a lot of traditional hulls have the drains at the forward end of the cockpit down through the hull further forward.

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Old 21-04-2016, 17:11   #8
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Re: Self-Draining Cockpits For Small Boats

Guess we should mention that many folks have the drain on the port side of cockpit sole cross over and drain out to the starboard side hull and vice versa to keep the cockpit free of sloshing water when heeled in those boats prone to slosh.
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Old 21-04-2016, 19:00   #9
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Re: Self-Draining Cockpits For Small Boats

"Boats with soles below WL have no choice but to put their drain outlets below WL."

I am not clear on this one. How come the cockpit does not back - flood?

BTW When you calculate, mind even a 'small' cockpit may easily add 1000 pounds of weight (when flooded, e.g. in a wipe out) to the aft part of the boat lowering the cockpit sole by 4 to 8 inches (versus wl), easily. Solutions for small boats: small, high sole cockpit (BCC style), or open deck cockpits (Minitransat style).

Have fun designing.

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Old 21-04-2016, 23:12   #10
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Re: Self-Draining Cockpits For Small Boats

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"Boats with soles below WL have no choice but to put their drain outlets below WL."

I am not clear on this one. How come the cockpit does not back - flood?

They do flood...

Sunfish and similar you sail with wet feet. Occasionally, if you manage to go fast enough the water gets sucked out by venturi effect.

As I noted above... there are boats that simply gave up and have huge openings in the transom so the water can get in and out more easily.

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Old 22-04-2016, 01:51   #11
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Re: Self-Draining Cockpits For Small Boats

My comments re below the waterline soles/drainage were mixed up...

...and not particularly relevant to cruising boats anyway.

The key point I'm trying to make is that boats with slightly above waterline soles could benefit from smaller drains at sole-level, and larger drains higher up the transom (or on whichever surface in the cockpit the drains are placed), in order to reduce the risk of backflow, without losing drainage capacity in serious flooding situations.
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Old 22-04-2016, 03:01   #12
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Re: Self-Draining Cockpits For Small Boats

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Originally Posted by KISS View Post
My comments re below the waterline soles/drainage were mixed up...

...and not particularly relevant to cruising boats anyway.

The key point I'm trying to make is that boats with slightly above waterline soles could benefit from smaller drains at sole-level, and larger drains higher up the transom (or on whichever surface in the cockpit the drains are placed), in order to reduce the risk of backflow, without losing drainage capacity in serious flooding situations.
OK, KISS, that is a reasonable approach... big but higher up drains to take the brunt of a big pooper, and lower, smaller ones to deal with the dregs.

One thing to remember: when conditions are so severe as to promote pooping, the boat usually has enough vigorous motion to slop out a considerable portion of cockpit burden water.

Jim
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Old 22-04-2016, 06:58   #13
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Re: Self-Draining Cockpits For Small Boats

Yes. Exactly.

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Old 22-04-2016, 08:26   #14
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Re: Self-Draining Cockpits For Small Boats

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Originally Posted by KISS View Post
I couldn't tell you which designs, but some people certainly drain their cockpits below WL, even into the bilge (!), which would appear (to me at least) to be quite insane if you had the option of draining above WL (thus I assume they don't?).

In any event, there's no such thing as a drain too high above WL.

So perhaps the concept in the OP could be of use.
Sir, to be blunt. You'd be wise to get both your; facts, & Especially, thinking straight on this topic (& several others - SIC).

As I kind of doubt that the USCG or other regulatory bodies, are going to let a manufacturer sell a boat which, by design, has it's cockpit draining into the bliges. On what planet does that make sense?
For the simple reason that a fair number of such boats would quickly turn into submarines.

And such instances tend to cause lawsuits for; those officials who said the design was okay to sell, commercially. Plus suits generated by the families who lost relatives & friends, due to such stupidity of design.
That one would be a slam dunk for anyone who went to 3min. of law school.

Also, cockpits which drain below the WL are not new at all, in addition to working quite well on some boats. I used to own one.
It ain't as if the plumbing on such is rocket science.

Plus, what kind of boat of any size (so that it has plumbed cockpit drains) are you speaking of which has it's cockpit sole below the WL, even when heavily laden? There are laws regarding such things as well. Not to mention common sense.
I've even been out in signiicant seas, on a 14', or 15' West Wight Potter, with 5-600lbs of crew in the cockpit, & we all had dry feet as I recall.

So I'm at a loss as to where you're coming from, or why.
If you have an issue with, or question on, a specific boat, then folks around here are happy to field them. But questions of other sorts are referred to as Trolling. Which is frowned upon. Heavily.

Ever hear of the term "Loose Cannon"? And are you familiar with the significance of one?
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Old 22-04-2016, 13:20   #15
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Re: Self-Draining Cockpits For Small Boats

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OK, KISS, that is a reasonable approach... big but higher up drains to take the brunt of a big pooper, and lower, smaller ones to deal with the dregs.

One thing to remember: when conditions are so severe as to promote pooping, the boat usually has enough vigorous motion to slop out a considerable portion of cockpit burden water.

Jim
Thanks Jim

Have you ever seen this set up on a boat? It seems like a fairly obvious solution to the backflow problem on smaller boats, but I'm not aware of anyone doing it.
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