Quick draining cockpits a myth ??

catmandoo

catmandoo

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My catamaran has a large rectangular cockpit with three 1.5 inch diameter drains located at 3 of the corners draining down directly to the sea through the bridge deck . If it were to be hit by a big sea with the wheel house door closed the potential initial capacity would be about 1 cu metre of sea water weighing about 1 tonne which might significantly affect the stabllity of the boat not counting the weight of other streams of water running over other parts .( might not even be able to open the wheelhouse door )

The question is whether the drains are sufficient enough to clear the water quickly enough to regain stability . . The time to empty the cockpit can be calculated by considering the cockpit as a 0.5 metre deep tank with three external mouthpiece orifices in the bottom and a decreasing head or can be found by a practical experiment of filling it up with water in port and pulling out plugs in the holes simultaneously .
Arriving at a time however poses the question . Is it OK before the next wave arrives or in severe weather will the cockpit remain permanently full as each succesive wave keeps it topped up ???

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Your drains don't have a bad diameter but they're nothing compared to having full height openings at the back of the cockpit, as many catamarans do. I'm not sure why a catamaran would be designed with a bathtub cockpit, given its height above the water.

The most effective and safest monohull cockpit drainers are similar with walkthrough sterns. I had a Beneteau with a nice false stern which slotted in like a washboard and had a 2" gap at the bottom, along with a similarly detachable stern lid. Water did come in, particularly in a following sea, but not much and never got above the draining slots on either side of the cockpit floor.

Obviously water cleared pretty much instantly including a time when a wave broke over the back of the boat, completely immersing a crew member who was lying on the cockpit seat. Within seconds he'd reappeared, and almost immediately the cockpit was empty again.
 
The cock pit top is in fact higher surrounded by lockers acting as seats etc with a further section acting as a back rest 300mm high except at the stern where there is an opening about 600 by 300 mm which could act as a walkthrough .as well as an entrance point for water

So I suppose the designers made allowance for the potential weight of water of the lower section . I hope

However when you say adequate it depends on the frequency at which the following waves break on the stern or sides
 
What type / size cat is it? It is impossible to calculate the effect of 1 ton of water without knowing the displacement of the boat. My first reaction is that I ton loaded in the cockpit would probably be insufficient to affect the stability or trim significantly if it's say 36 ft or over....
 
I would suggest that if the conditions are bad enough for a high frequency of breaking waves to fill the cockpit, the motion of the vessel itself will help throw any major excess water back to where it belongs.
 
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