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Old 16-04-2014, 22:48   #1
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Cockpit Drain Above or Below Waterline?

Hopefully this is the right forum for this question. I've got an Endeavour 37, which we plan to do an extended cruise on. I'm struggling with the large number of large below water thru-hulls. There are seven 3/4 to 1.5 inch thru hulls plus 2 small chain locker drains all below the water line. Here's my question:
The cockpit drains are 1.5 inche dia. and drain to thru-hulls approximately 2 feet below the water line. The cockpit floor is approximately 21 inches above the waterline. Can I move the drains to an above the water line discharge maybe 15 inches below the drain, and 6 inches above the waterline. Perhaps by putting a check valve on them to keep a wave from pushing water up into the cockpit.
The other question is: Do sink drains need to be 1.25 inch diameter. It's seems odd to have a tiny head sink, draining into a giant 1.25 inch thru-hull. Do people have smaller drain lines? Any advice here would be greatly appreciated. Paul
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Old 17-04-2014, 01:26   #2
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Re: Cockpit drain above or below waterline?

Cockpit drains draining below the water line are a funny thing. My current boat has the same set up as yours and I discovered not long after buying it that the single hose clamp clamping the hose to the thruhull had missed the nipple altogether. Goodness knows how long it had been like that for, but the hose had never popped off, so in a way that kind of instills some confidence that the drains will remain intact.

Now back to your question, water would enter the cockpit regardless of outlet height. It is a function of cockpit floor height above the waterline. This also means heeled waterline as well. If the "fall" between the drain and outlet is not enough though, you may have problems with draining in a seaway as the water will slosh back into the cockpit before it escapes the drain plumbing. Seas can also enter the drain if they rise higher than the floor with the boat's motion, but I guess rubber flap valves could be used to prevent this.

Your sink drain through hull only needs to suit the size of the drain. My washbasin drain in 3/4" which drains a bit slow, but at least you cant loose your wedding ring down it. Perhaps the larger through hull has been repurposed from a previous function e.g. toilet outlet.

No one like lots of underwater through hulls, but plenty of boats have them. If you maintain them I really can't see why they would need to be repositioned. I personally wouldn't be bothered to move mine.
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Old 17-04-2014, 05:38   #3
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Re: Cockpit drain above or below waterline?

Of the four I had on Vigah, one was below the WL. I have attached pics of the SS coupling I cut off after I moved the drain above the WL. BTW, the clamp was broken and that was why I disconnected it. It was also in my way trying to get into the engine compartment. I also never figured out why the drains were crossed. stbd drains drain on the port side, etc.

Over time, I have removed three excess seacocks located below the WL. Be honest, how often will you actually remove the hose to check the barb fitting? Granted, the barb should not have been SS on the brass seacock, but the boat was manufactured that way. Visual of the clamps, certainly.
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Old 17-04-2014, 06:01   #4
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Re: Cockpit drain above or below waterline?

I'll bet they were crossed on the theory that the downhill drain would of course be the primary drain and attaching it to the uphill through hull would have that through hull out of the water. Probably slowed draining though as there was less drop
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Old 17-04-2014, 11:36   #5
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Re: Cockpit Drain Above or Below Waterline?

Leave your cockpit drains alone.
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Old 17-04-2014, 11:43   #6
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Re: Cockpit Drain Above or Below Waterline?

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Originally Posted by Terra Nova View Post
Leave your cockpit drains alone.
The cockpit drain thing was figured out a long time ago. About the only thing left to argue is should they cross below deck.
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Old 07-07-2017, 03:41   #7
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Re: Cockpit Drain Above or Below Waterline?

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Originally Posted by Terra Nova View Post
Leave your cockpit drains alone.
I'm glad I found this thread. My boat's cockpit has the outlet below the waterline. Two drains at the front drain to a single skin fitting on the starboard side. The port side drain goes to a T-fitting. I thought it was really bad design and wanted to relocate the outlet to above the waterline. That is a lot of work I need not do.

Thank you.
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Old 07-07-2017, 04:01   #8
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Re: Cockpit drain above or below waterline?

Quote:
Originally Posted by a64pilot View Post
I'll bet they were crossed on the theory that the downhill drain would of course be the primary drain and attaching it to the uphill through hull would have that through hull out of the water. Probably slowed draining though as there was less drop
You may be saying this, but let me restate it to make sure I understand. My opinion is that they are crossed to keep water from back flowing into the cockpit under heel. If the windward throughhull is out of the water, then it would prevent water from flowing into the cockpit.

To the OP, you mentioned a check valve. I wouldn't do this, just because there is a possibility of it not being open when you want it to be. Could from debris, corrosion, or what have you. I would make the path to get water out of the cockpit as simple as possible. In case someone takes this the wrong way, of course keep the seacocks in the event of hose failure.

We are a steel boat and have two straight 1-1/2" pipes from the cockpit straight down to the water. No throughulls, just pipe welded at the top and bottom. Under heel we do get a bit of water in one corner of the cockpit.

Concerning the head sink, the only thing that a large drain does is lengthen the time between cleanings of hair, soap gunk, and other smelly stuff.

Cheers!

Steve
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Old 07-07-2017, 04:55   #9
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Re: Cockpit Drain Above or Below Waterline?

I welded up the underwater through hulls on my aft cockpit steel 34 footer and welded in solid 3 inch 316 steel pipe drains above the waterline directly abeam of the aft end of the cockpit well. It worked perfectly for me, no water in the cockpit at any angle of heel or boatspeed. I expected to have issues with waves forcing a jet of water through the pipe into the cockpit, but it never happened in 3000 miles of open ocean.

Ideally the drains are better in the forward end of the cockpit as the quarter/stern wave is further aft, but it would have effected my quarter berth access, and in the event it worked perfectly even from the aft end near the quarter wave.
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Old 07-07-2017, 05:10   #10
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Re: Cockpit Drain Above or Below Waterline?

Quote:
Originally Posted by Paul Mazza View Post
Hopefully this is the right forum for this question. I've got an Endeavour 37, which we plan to do an extended cruise on. I'm struggling with the large number of large below water thru-hulls. There are seven 3/4 to 1.5 inch thru hulls plus 2 small chain locker drains all below the water line. Here's my question:
The cockpit drains are 1.5 inche dia. and drain to thru-hulls approximately 2 feet below the water line. The cockpit floor is approximately 21 inches above the waterline. Can I move the drains to an above the water line discharge maybe 15 inches below the drain, and 6 inches above the waterline. Perhaps by putting a check valve on them to keep a wave from pushing water up into the cockpit.
The other question is: Do sink drains need to be 1.25 inch diameter. It's seems odd to have a tiny head sink, draining into a giant 1.25 inch thru-hull. Do people have smaller drain lines? Any advice here would be greatly appreciated. Paul
I added two cockpit drains that drain to the transom above the waterline. Exterior mounted ball scuppers control backflow and cannot "stick" in either the open or closed position.
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Old 07-07-2017, 05:17   #11
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Re: Cockpit Drain Above or Below Waterline?

Here is a picture of Snowpetrel showing the old welded up skin fitting location near the skeg, and the new cockpit drains above the waterline aft primed with white paint. They might have been 2 1/2 inch pipe rather than 3"? Anyway big solid and unrestricted pipe that drained the cockpit real quick.



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Old 07-07-2017, 05:20   #12
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Re: Cockpit Drain Above or Below Waterline?

We have above wl cockpit drains. There is a 2 inch pipe across the hull level with the aft end of the cockpit , with tees corresponding to the two aft ends of the cockpit.
Our galley sink also flows into this pipe.
Our cockpit floor is only 6 inches above wl and we do get inflow, primarily from the uphill side when sea is rough but it is manageable.
We used to have pipes to below wl but on a steel boat they were impossible to keep coated.
Our only below wl thru hulls now are the engine inlet and the toilet outlet.
The head draws its water from the engine inlet, and the head sink drains into the head.

Regards,
Richard
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Old 07-07-2017, 05:45   #13
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Re: Cockpit Drain Above or Below Waterline?

Don't think even a minute that cockpit drains are set perfect from the factory. Some are adequate and some just plain stupid or even dangerous. There are only two reasons to have them discharged below waterline. The other one is to hide them out of sight and the other one is a poor excuse of lazyness..

BR Teddy
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Old 03-10-2017, 00:13   #14
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Re: Cockpit Drain Above or Below Waterline?

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Originally Posted by Terra Nova View Post
Leave your cockpit drains alone.
As mentioned above, my cockpit drains to single through hull below the water line.

Having seen the ball valve needs replacing, I've decided after all to relocate the outlet to above the waterline. Two outlets, each just above the waterline in line with front of cockpit.

Bad idea?
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Old 03-10-2017, 00:52   #15
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Re: Cockpit Drain Above or Below Waterline?

When you think about it, most cockpit drains are truly tiny. As even if they're 1.5" (in theory), the internal diameter is greatly reduced by the hose barbs & nipples to which the hoses connect. And few boats have drains that are large enough, & numerous enough to empty the cockpit prior to another wave filling it in boisterous conditions.

You'll notice that on a lot of racing boats from the pre open transom era have a pair of large scuppers at the cockpit's aft end, which run through large diameter pipes glassed in place, that exit out the transom. Often even these are a touch small, given the size of cockpits on racing boats. And I'm a fan of replacing the smallish 1.5"-2" pipes, with something more akin to sewer pipes if the boat's to spend time offshore. Say 3"-4" diameter minimum, with flaps over their exits to prevent waves from splashing into the cockpit through them. And perhaps a piece of mesh, or similar to prevent small items from falling through them when dropped in the cockpit floor.

Also, said transom exiting drains needn't be round. You can fabricate some square or rectangular tubes out of fiberglass (or plastic, or metal), & glass them in place in the cockpits aft corners, as well as to their exit points in the boat's transom.

And even with these, if the boat is equipped ith cockpit drains at her forward end, it's wise to leave them in place too. As the boat will have been designed such that most of the water in the cockpit will flow "downhill" towards them. This, except when in extremis, such as when the cockpit is getting filled semi-regularly. Which is when transom sewers (above) come in real handly.

Note that if you do glass tubing into the transom, the insides of the pipes need to have some UV protection for much of their length. So paint their insides after installing them.


EDIT: IMO the only way a cockpit drain can be too big is if it can swallow a winch handle & donate it to Neptune
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