Moving Cockpit Drains to Transom?

[chasfgr]

Originally Posted by Mike Burch

In the nineteenth century a Frenchman named Poiseuille discovered that the rate of laminar flow in a cylindrical tube varies as the fourth power of the radius.

Since the cross-sectional area varies only as the square of the radius (good old "Pi x R squared"), this is somewhat counter-intuitive. Most of us would imagine that doubling the area would double the flow rate, but in fact it quadruples it. So a pair of 2" diameter drains will in theory clear your cockpit sixteen times faster than a pair of 1" drains.


Of course, in the real world the flow is not going to be purely laminar, at least at each end of the drain, so the effect will be somewhat less than M. Poiseuille would have us believe. Nevertheless it points to the huge improvement that increasing the size of the minimal drains the builder has installed will make in the event of a pooping. The flow rates of 1", 1.5" and 2" drains are in the ratios of 1:5:16. In any normal-sized cruising boat, 2" drains should be possible, and will probably be adequate.

The flow rate also varies inversely as the length of the tube, so doubling the length of the tube halves the flow rate.

So a short fat drain wins over a long skinny one every time.

As for draining the cockpit into the bilge, words fail me.

I am surprised that words would ever fail a Kiwi.
I got some socks from Ashburton (family connections) and the duty was almost the same price as the socks - £14.00 socks even made in NZ merino are a trifle outside my expectations.
Of course it's the UK government we should blame, just wait until the next time I see Michael!!!

[HeinSdL]

I started sailing back in the 70's on traditional Dutch sailing vessels, you probably know the type with the side boards, known locally as "platbodems". The one my family sailed on was a converted fishing vessel and for sure there were issues with keeping the water out. In the very old days (when these vessels were completely open and relied on sails alone) the crew would have spent a lot of time keeping the vessel afloat (as well as hauling in fish). But these fishing vessels were absolutely not meant to take further out than the shallow waters surrounding Holland, so North Sea and no further.

Today, I can't imagine there is any sailing yacht afloat with a cockpit floor lower (or even close to) the water line. At best there would always be water in the cockpit and at worst the yacht would not survive normal conditions one may encounter offshore. Even more so, and for the same reason as those poor fishing crews having to fight to keep their vessels afloat, I cannot imagine cockpits draining into the bilges.

So that leaves open the question of how to drain. Well given that the cockpit floor is already above the waterline, why go below it again with the plumbing? Hence OP question answered in my view, keep the drains above the waterline, via the stern with large diameter drain pipes.

[rla]

Originally Posted by sailortype

and then have enough pumping capacity to empty the bilge before the next wave..?

or do you just keep collecting them in the bilge... with an even trim..?

its a rare event, so you only have one or two to deal with, and the trim of the boat alters little. Unlike a small sealed cockpit, or with too smaller drains, where the one wave will bring down the stern and cause other waves to easily enter.