cockpit drains

I'm building a 32 ft sailbaot and am confused about cockpit drains.
I've read they should be in an x patern such that port side drains to starboard
and vice versa. I would think that if you are heeled over to far they wouldn't
drain. Also on small sailboats the drains are sometimes underwater and the motion of the hull sucks the water out faster so wouldn't it be better to drain on
the heeled side. I know this is simple but can't seem to get my head around it ... any thoughts Thanks

 

It does take some playing, especially if you have a particularly wide cockpit. You're right that if your anticipated heel angle exceeds the angle of the 'arm' of the X from the horizontal, draining stops; so steeper is better. But you're stuck with the width of the cockpit, the height of the cockpit sole and the immersed section beneath.

If the cockpit is particularly wide and/or close to the waterline, you might consider exiting out the transom (to get a bit more flexibility with a 'more' centerline exit location, but I still probably wouldn't go straight out) or moving your drains inboard to get a better angle (while accepting a pool outboard of the drain location).

JPC

 

Outlet Shape

What is the recommended shape of the discharge?

The typical thru-hull fitting with the donut shape on the exterior of the hull likely creates some drag below the waterline. A smooth shape with the drain angled away from the direction of travel probably creates a little bit of suction in the drain pipe.

What should the hole look like? A tear drop with the big end leading? A tear drop with the big end trailing? A truncated parabola with the flat edge trailing? A hyperbolic shape? A sharp edge forward and a tapered edge at the aft end? Something 3-dimensional like a mast exit for a halyard?

 

You seem to want two different things from your cockpit discharge. On one hand you want a drain, which typically cross to the opposite side, but on the other hand you'd like them to be self bailing scuppers too.

Crossed drains work pretty well on larger craft (over 30 - 35 feet). When the cockpit sole gets close to the LWL or has to be wide to accommodate seated crew, then issues crop up and a transom drain, well or scupper is the usual choice.

If your cockpit sole is a foot over the LWL and you have some depth to the hull in this area (most newer designs don't) then crossed drains will work fine. If you cockpit sole is particularly wide or close to the LWL, then run the drain hoses directly aft and exit the transom or below it, if you have some overhang.

Self bailing scuppers can be purchased, but I don't like them much, except on dayboats. I would suspect you'd get more drag trailing an angled section of pipe or hose, trying to get some suction, then a traditional thru hull outlet, even if it was close to the hull's surface. I've seen racers fair the crap out of them in an effort to save a 20th of a knot in boat speed, but frankly, unless your hull has many of them, you shouldn't be concerned. Set it flush to the hull, which requires some grinding, reinforcement and fairing, then just the hole is exposed.

 

I'm re-doing the cockpit drains on my Catalina 30. As installed at the factory they are a hazard.

The transom is higher that the cockpit sole, so running the drains out the transom is out.

The shortest, most direct path for new through hulls puts the drains below the waterline.

Are there any problems that I should be looking for? Any reason that the drains should be or have to be above the WL?

There is no room to cross the drains in an X (PAR is right as usual).

 

No, the drain can be below the LWL, but I would caution, that the sole needs to be at least 8" over the LWL or some minor seepage can get in from following seas passing under her stern or as the boat pitches in a seaway. It's no big deal really, it'll drain back out as soon as the boat stops squatting her butt.

Take as direct a route to the thru hulls as possible and use the biggest drains/hoses you can find. A cockpit can hold enough water to cause a well handling boat to wallow badly, usually just when you need to avoid a broach or some sharp pointy rocks (at least that's my luck).

 

What we have done as a safety measure in the past is to put a large drain-pipe 2-3 inches above the cockpit floor and out the transom, that way, when you get a lot of water in the cockpit the slow floor drains only have to do the last bit.

Yoke.

 

Thanks!

Once the new drains are in, I'll fill the cockpit with water again and time how long it takes to empty. With the drain as installed by the factory the drain time was so long it was frightening.

If it is still too slow for peace of mind, I'll add "yokebutt pipes"

 

After a big sea has boarded you, filling the cockpit, 30 seconds can seem like eternity, a minute may be more then you can stand (or the boat). Try it, set an alarm for 60 seconds and then try to think of a wallowing boat, in a beam sea and what you'd be trying to do waiting for the ton (no kidding) of sea to vacate the cockpit. My Arthur Robb offshore 35 (CCA style yawl) could drain her cockpit in less then 20 seconds. It had four 3" drains, one in each corner of the foot well. The two aft, drained under the counter and the forward ones crossed over. It originally had two 1 1/2" drains that crossed. I fixed 'er good.