Semi-draining cockpit?

[Kaa]

Most boats nowadays have a self-draining cockpit. The problem with it is that the sole is quite high and if a large cockpit with inadequate drains gets swamped, you get a huge mass of water sloshing above the waterline level for a while -- not good for stability at all.

In a non-draining-cockpit boat the sole is usually considerably lower and some water in the cockpit actually tends to stabilize the boat. However the problems with a non-draining cockpit are obvious.

I wonder if any boat implemented a SEMI-draining cockpit, meaning a both a low sole *and* drains above waterline. This way a few inches of water in the cockpit would stay there until pumped out, but above a certain level the water would start pouring out through the drains.

In the specific example I have in mind, a pocket cruiser has a low sole and a non-draining cockpit, but it also has a motor well for an outboard. I am curious if making an above-the-waterline drain into the motor well would be a good idea.

Kaa

[PAR]

The biggest bilge pump you can install, will not move near as much water, as you need to move when pooped. Big, well located drains are the ticket. I once saw a wholesome sailing cruiser with six 3" drains in the cockpit. If pumping up to a well is your only option then install the biggest pump you can afford. Another option is self bailing scuppers, which can remove water from the cockpit if the sole is below the LWL.

[Willallison]

It's an interesting idea, but a few problems spring to mind - quite apart from the very real one that PAR has already suggested.
You eluded to the 1st yourself, in that water makes for a very poor ballast material unless it's movement is restricted. So whilst it's trues that by adding weight in the bottom of the cockpit you might be lowering the CG, that situation can only be guaranteed as long as the vessel remains upright: which rather defeats the purpose.
Also, unless you have a particularly low and deep outboard well, then it is likely to be quite a lot higher than your cockpit sole, meaning that you would need a lot of water onboard before it started to drain. A deep / low well is a bad idea as it can be prone to being swamped in a following sea.
You'd also need to ensure your scuppers couldn't backfill the cockpit.

Why not have scuppers in the topsides?

[tom28571]

Originally Posted by Kaa

In a non-draining-cockpit boat the sole is usually considerably lower and some water in the cockpit actually tends to stabilize the boat. However the problems with a non-draining cockpit are obvious.

Kaa

Not so.

If you ever have a boat with significant water in the sole that is either above or below the waterline and unrestrained, you will quickly see the fallacy of this argument. Such water makes the boat very sluggish in control as well as less stable, not more. It will follow gravity and always be on the wrong side. Ask any racing sailor about this.

While the possibility of being "pooped" does exist, it must be very rare. In 40 years inshore and off, I have never come close to experiencing it. I have had waves come aboard on a reach though but they gave no real problem.

There are many boats with non draining cockpits. Problems with rain and big spray are much more real than a hypothetical pooping. A cockpit cover, side curtains and a good (two) bilge pump is their salvation. Don't like them myself and always want a self draining cockpit.

[PAR]

Tom is correct and I forgot to mention it. This is the effect of free surface of liquids. Because the water is not restrained (full tanks, baffles, etc.) the weight of it will run to the leeward side, causing the CG to move in the same direction. This, understandably will result in a reduction of the righting couple. This effect also has a bad dynamic relationship with stability, because the roll moment of the free surface water (swamped cockpit) will be different than that of the hull, depending on the roll phase and if they are opposing each other.

I have had a swamped cockpit, but I remember a broach, heeling way over and coming up with a full cockpit. It seemed like forever for the cockpit to drain and the boat handled like a pig, very unresponsive to helm input. I've also had big boarding seas flood the cockpit while running before steep breaking seas. I can count the occasions with just a few fingers, but it will put the fear of God in you pretty quick. Any dinghy sailor knows how a boat handles when she's got a belly full of water, sloshing around.

[Willallison]

See - I told you so!

[PAR]

pppppllllllltttttt . . .

[Kaa]

Well, evidently I wasn't too successful at clearly expressing myself :-)

But let's cut to the chase. If I have a boat with a non-draining cockpit (but with a bilge pump dedicated to that cockpit), would it make sense to install some drains or scuppers at the level higher than the cockpit sole?

The reasoning goes as follows. The bildge pump can take care of the small amounts of water from rain or spray. But if I take green water into the cockpit, I want to get rid of it ASAP, thus the drains. The drains will not remove ALL water from the cockpit, but whatever few inches remain can be taken care of by the bilge pump at its slow pace.

As to the likelihood of getting pooped, well, I don't intend to get my cockpit full of water, but you know, things happen

[Willallison]

Kaa - no I think we all understood your intentions, it's just that the idea of accepting having water sloshing around in the bottom of a cockpit sends shivers up the spine of anyone concerned with stability.
There are further things to consider - not the least being that you don't really want to be trapsing around in several inches of water. Also you would probably need to incorporate some kind of 'sump' that said water would run into before being pumped out: bilge pumps are notoriously bad at sucking out the last bit, and if it's spread over the flat surface of a cockpit sole then I doubt you'd ever get rid of it all.

At the end of the day, if you're stuck with a non-self-draining cockpit, then yes, I'd personally say that the scuppers (provided they are prevented from allowing back-flooding) would be a good idea.

The closest I've ever come to being swamped was from water coming over the bow.... well, to be more precise, I stuffed the bow of our 25ft fishing boat into the back of a wave. It popped one of the front windscreens out and I enjoyed a quick (very cold) bath of a few hundred litres of water!

[PAR]

Pooping isn't very common, but it does happen. Much more often is a large boarding wave (or several in a row) will deposit enough water in the cockpit that drains are necessary, just to make life more comfortable.

Yes, install the drains where you can (or have to). The design limits options so you'll have to work with what you got. There's no reason they have to exit above the LWL, but again check valves, flappers, crossed drains or some other method of preventing back flooding will be necessary. A sump is a good idea and a grating will help with the little remaining water that the pump doesn't toss over the side.