Cockpit Drains - cross-over or not ?

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Cockpit Drains - to cross 'em over or not, that is the question ... ?

On another forum, this question has been raised - specifically, when considering the cockpit drains as fitted to a Corribee or Coromandel. My immediate thinking was 'of course they should', and I'd bet money that anyone else reading this post would say the same. But - let's stop and think about this ...

The Corribee has it's drain outlets placed just inboard of the twin keels, and so in all but the most extreme of situations, both outlets will remain below the water-line. So - if the boat is heeled-over such that the water level in the leeward drain hose is (say) just one inch below the cockpit floor, then it will be one inch below - regardless of whether the leeward cockpit drain leads to the leeward outlet or to the windward outlet.

Indeed, if one then considers how the cockpit will drain whilst heeled, it would surely be slightly easier for water to exit via the shorter vertical (uncrossed) hose. And, in the case of the Corribee/Coromandel, uncrossed hoses would significantly facilitate access to the under-cockpit storage area.

But this would seem to fly in the face of conventional wisdom.
So - any thoughts on this one ?
 
Cockpit drains generally want to be as short as possible, to drain with the least resistance. I can't see much merit in crossing them over, unless it's to do with water spurting up them when the boat slams in waves?
Inboard of the keel... is this significant? A low pressure area on the leeward keel and vice versa?
 
The main reason for the crossover is to stop the ingress of water when heeling because if you didn't crossover both the outlet and cockpit floor level would be below sea level.
 
Read his post again.

Both outlets are near the keels, so both are always below the waterline whether heeled or not. Doesn't matter if they are straight or crossed over - both will always be deeply immersed.

Draw it out on a piece of paper, and rotate the paper as if the boat was heeling.
 
If you don't cross them over then on a heel the lower one will give direct access for water to flood in to the cockpit.

They cross to keep the exit for the cockpit drain lowest in the water higher to avoid flooding.

The pipe leaves the cockpit and does a tour of your interior making it as high as possible on the side furthest away from the drain. All for the above reasons.

They cross for a reason.
 
There is only any point if the crossed drain lifts out of the water when sailing. If the lower corner of the cockpit goes below water level, and the drain oulets never come out of the water, crossing has no effect.
 
The trouble with the Corribee is that the cockpit floor is very close to the waterline so close that I understand that with more than 2 people in the cockpit the floor is awash anyway

If the drains were not crossed there is a chance that water would flood up the leeward one when heeled.


I actually know someone who is moving the drains from the front of the cockpit to the back (the floor is a bit higher at the back) and constructing a new floor above the old one to slope down to the repositioned drains. Sorry I dont know any of the finer details I just know he is doing it (Also strengthening the whole hull as it is one of the later lightly built ones and reducing the size of the skeg and creating an outbord well)
 
"They cross to keep the exit for the cockpit drain lowest in the water higher to avoid flooding." How exactly - is it just because there is lower water pressure acting at the higher exit, resulting in reduced (not zero) flooding?
As regards the crossed pipe being higher as it tours the hull, I've read that it's important to make the run as simple as possible with a continuous fall from inlet to outlet, to avoid potential blockages and airlocks.
Out of interest, Jonny Moore recently made it most of the way around Britain in a Corribee whose drains are straight-through: http://www.jonnymooresailing.com/cockpitdrains.
I'm prepared to believe there is a benefit in crossing the drains, but just can't figure out the science. As the OP says, straight-through drains would yield valuable space in a Corribee (eg. for a spare battery).
 
[ QUOTE ]
... If the drains were not crossed there is a chance that water would flood up the leeward one when heeled.

[/ QUOTE ]
If the leeward cockpit drain drops below the waterline, then water WILL flood into the cockpit regardless of whether the drain-pipes are crossed or not, as BOTH outlets are already below the water's surface. Whether one outlet is higher or not than the other - or whether an outlet is higher than the drain itself - cuts no ice: the fact is that if both drain and outlet are both below the waterline, then water WILL enter into the cockpit from below.

I know that non-crossing-over sounds counter-intuitive - I've been a fully paid-up member of the cross-over club for years, but once you can see the fallacy, then there's no going back.
 
[ QUOTE ]
as BOTH outlets are already below the water's surface.

[/ QUOTE ] I was assuming that the exit would then be above the water but I guess thats not necessarily the case. I must confess I dont know exactly where the old outlets on the Corribee were. Mine are only just below the water line so when heeled one outlet is (I think) above the water but my cockpit floor is well above the water line.
 
On a boat with a cockpit floor close to ar at waterlevel, a PROPERLY DESIGNED cross-over arrangement will work.

As the boat heels to the point the lower drain is below water level the outlet for that side should be coming out the water.
Thus water is prevented from flowing into the cockpit through the drain.
BUT if the water comes in over the coaming, it will drain to the point where the level in the cockpit is the same as the "upside" drain through-hull.
Having a few gallons of water sloshing around after a pooping (ie occasionally) is better than having a few gallons sloshing around whenever the cockpit level dips below water level (ie most of the time).
 
I had a Corribee, but it was (possibly like yours??) not factory finished.
The result is that holes ended up in different places on the hull....
Ours DEFINATELY NEEDED the cross pipes, but it was a fin-keel (if it's pertinant).
The paper with "angle of dangle" calculations is all well and good, however, it's when underway that water is forced up into the cockpit!
We had the same problem with a shipman 28(it even came up the seat drains!)and pre-empted it on an ericson 39. All these boats dip their transoms when the going gets good, so the waterline as such is no longer relevant.
 
I have never been a fan of cockpit drains anyway, but they were designed into Wight Dawn so I have to tolerate them. I always get nervous about a bit of plastic pipe being all that is between the sea and the bilge. What if it fails when I am off the boat? Should I close the seacocks when not in residence? This would negate the benefit of having drains. The only drains I have been happy with were on a wooden boat and the cockpit was well above sea level (well about 9" anyway.) The drains were trunkings (like centreboard casings) and they went straight down from the corners. No crossing. And no seacocks either.

On all my early boats, it was a bail-out job after rain. Not too bad on my converted 6-metre, which had a small cockpit and lots of deck, but a real pain on a YW Dayboat with its enormous cockpit.
 
I have two 1-1/2" drains on my Twister and I can't cross the pipes because there is a big Centaflex shaft coupling in the way.

It has not made the slightest difference, no water comes up the drains. The only time I get water in the cockpit is when it rains or when a sea comes over the coaming.
 
[ QUOTE ]
... As the boat heels to the point the lower drain is below water level the outlet for that side should be coming out the water. Thus water is prevented from flowing into the cockpit through the drain.

[/ QUOTE ]

Now THAT is the best explanation I've heard for using cross-hoses. Have a pint on me. /forums/images/graemlins/smirk.gif

I'm surprised no-one makes a simple flap-valve to fit in the hose - that way you could fit un-crossed hoses (for better drainage) without the water ingress problem.
 
One way cockpit drain valves usually work like the old ping-pong ball scuba valves, and as badly. Also they significantly reduce the rate of outflow if you take a big wave over the coaming, accumulated spray drains without too much problem. My Cutlass27 is going for a winter refit and i've looked at the general cockpit drain problem . The existing drains (plumbers sink fitting!) always have the sea slopping about 1 inch below the grid when the boat is level and not too loaded and i can't see the pipework through the engine space so i don't know if they are crossed, i do take IN water when heeled.
I think the problem is just simply that the cockpit floor is too low.Raising the floor when i put in a Bomar hatch might help, then i will have to work out the best place for two bronze (gunmetal!) seacocks. See the Lackey sailing (Pearson)website for help.
 
;1888316 said:
Cockpit Drains - to cross 'em over or not, that is the question ... ?

On another forum, this question has been raised - specifically, when considering the cockpit drains as fitted to a Corribee or Coromandel. My immediate thinking was 'of course they should', and I'd bet money that anyone else reading this post would say the same. But - let's stop and think about this ...

The Corribee has it's drain outlets placed just inboard of the twin keels, and so in all but the most extreme of situations, both outlets will remain below the water-line. So - if the boat is heeled-over such that the water level in the leeward drain hose is (say) just one inch below the cockpit floor, then it will be one inch below - regardless of whether the leeward cockpit drain leads to the leeward outlet or to the windward outlet.

Indeed, if one then considers how the cockpit will drain whilst heeled, it would surely be slightly easier for water to exit via the shorter vertical (uncrossed) hose. And, in the case of the Corribee/Coromandel, uncrossed hoses would significantly facilitate access to the under-cockpit storage area.

But this would seem to fly in the face of conventional wisdom.
So - any thoughts on this one ?
Click to expand...
 
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