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Old 28-08-2013, 16:57   #16
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Re: Cockpit drains

Matt,

I suggest you take a seat in your forward settee, looking aft. Envisage the rail under water, and where the waterline would be.

I think you will see that under your proposal, the cockpit will not drain. Worse, it will backfill though your proposed drains.

If you take a cross section from some of the diagrams I gave you, you can do the above exercise in a more scientific way.

While you are envisaging the waterline with the rail under water, you might also consider the galley sink drain and the raw water intake to the engine and the outlet to the head. There are reasons for closing seacocks in a seaway.

Taking the drains aft is not an option, unless you have them running in a continual downward line, through the airspace above your bunk and in the lazarette.

I believe the only acceptable drainage arrangement for a centre cockpit is the one you currently have in place.

As a further thought, I have found it useful to mark the static waterline at several points inside the boat.....in the engine room, and the head. These marks can help when re-doing plumbing. I very nearly made a disastrous mistake on the engine exhaust system by not clearly thinking through waterlines.

Regards
Lee
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Old 28-08-2013, 17:05   #17
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Re: Cockpit drains

Sometimes the easiest solution is to simply keep what you have in good shape. :>)
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Old 28-08-2013, 17:31   #18
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Re: Cockpit drains

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Originally Posted by banjoship View Post
Matt,

I suggest you take a seat in your forward settee, looking aft. Envisage the rail under water, and where the waterline would be.

I think you will see that under your proposal, the cockpit will not drain. Worse, it will backfill though your proposed drains.
Thanks Lee, I will try what you suggest, but I am a bit suprised at the thought it would backfill, as, as far as I can see, that would imply the cockpit floor would be lower than the water line, which would imply the cockpit would fill anyway with the current arrrangement.

I certainly can see that on a starboard tack what I propose would not drain at greater than 15 degrees of heal, which may be a show stopper anyway, but since my inclinometer needs replacing, I am not actually sure what angle the boat usually sails at anyway.

Cheechako, you have a point and I will be replacing EVERY skin fitting that I do not decommsion for this very reason.

Matt
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Old 28-08-2013, 17:53   #19
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Re: Cockpit drains

"that would imply the cockpit floor would be lower than the water line, "

Precisely.


"which would imply the cockpit would fill anyway with the current arrrangement."

No.That is why the drains must be criss-crossed across the centreline. As per your current arrangement. hope that makes sense.

lee
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Old 28-08-2013, 18:20   #20
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Re: Cockpit drains

OK, I now have a headache. Not least of which because I am pretty sure they are not crossed over, but I will double check this arvo.

I thought the crossover was to improve draining when on an angle.

Like I said... headache now.

I CLEARLY have to do a bit more reading on that whole cockpit drain scenario, I just don't get it yet.

OK, just thought through the crossover thing a bit more, and I can sort of see how the crossover would improve things, but since both drain outlets are always completely submerged, I still feel that the cockpit would fill with water if either drain inlet were lower than the waterline.


Matt.

P.S. Dutch tall ships in Adelaide. Hooray!
Missed greeting them yesterday, had to work at the office. Boo!
Seeing them off on Sunday morning, in 10 to 15 knots of breeze. YAY!!!
They are heading your way Lee, will you go out to meet them?
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Old 28-08-2013, 18:30   #21
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Re: Cockpit drains

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Criss Cross the tubes....?
Can't, if the target is to have the exits above her waterline. If we did, with the hoses running nearly horizontal the lee one would not drain when heeled.

Move cockpit floor higher ;-) I must talk to her designer now ;-)

Cheers,
b.
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Old 29-08-2013, 05:02   #22
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Re: Cockpit drains

OK, I finally understand the crossed drain hose thing.

But for it to work requires that in the event you are healed over far enough for one side of the cockpit to be below the water line, then the crossed over "up hill" drain outlet has to have come clear of the water. Now there is absolutely NO WAY mine would ever do that unless I was completely airborne, in which case I have other more pressing problems. The outlets are next to the keel, nearly three feet below the waterline.

So I suspect I will find that they are not crossed over as there is no point.

But none of this helps me with my original dilemma, so it's back to the boat with a few bits of clear hose over the weekend, to observe the change in waterline while the boat is underway.

Should be a fun experiment actually.
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Old 29-08-2013, 10:54   #23
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Re: Cockpit drains

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Originally Posted by GILow View Post
OK, I finally understand the crossed drain hose thing.

But for it to work requires that in the event you are healed over far enough for one side of the cockpit to be below the water line, then the crossed over "up hill" drain outlet has to have come clear of the water. Now there is absolutely NO WAY mine would ever do that unless I was completely airborne, in which case I have other more pressing problems. The outlets are next to the keel, nearly three feet below the waterline.

So I suspect I will find that they are not crossed over as there is no point.

But none of this helps me with my original dilemma, so it's back to the boat with a few bits of clear hose over the weekend, to observe the change in waterline while the boat is underway.

Should be a fun experiment actually.
Why does the windward side have to come clear of the water? If the cockpit drain is higher than the exit (submerged or not) it will drain. However, The less height, the less force draining it.
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Old 29-08-2013, 12:38   #24
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The drain height also has zero affect on water entering the cockpit via the drains. If the cockpit drain goes below sea level, water comes in.
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Old 29-08-2013, 12:43   #25
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Re: Cockpit drains

yeah, it's interesting though, I have been surrounded by passing seas above my head sitting in the cockpit, cant remember the water coming up in the cockit drains though....maybe a little seeping... must be a time related thing... seas not over the drain top long enough for the hydraulic action to take place? or something like that. I doubt it would ever happen in a CC....
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Old 29-08-2013, 12:47   #26
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Re: Cockpit drains

The hydraulics and need for "head" is an interesting thing for sure. I had a customer once on an aluminum powerboat that was displeased because rainwater would sit in the cockpit accuulating maybe 1/2" of water at times. We added two 1" cockpit drains. It turns out the cockpit floor was dead even with the sea level. Now 1/2" of head is not much, it would take about 10 minutes for that measly 1/2" of water to drain.... (no head) and of course wold not drain at all unless the sea was very flat!
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Old 29-08-2013, 13:55   #27
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Re: Cockpit drains

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Hello Cruisers,

Our cockpit drains run in two 1.5" hoses from the floor of the cockpit, straight down through the engine bay to skin fittings just above and either side of the keel, about 1 foot or so below the waterline..

I have been doing a bit of measuring, and I THINK that the cockpit floor is about 1.5 feet above water level. It would be possible, therefore, to run the cockpit drains out to the starboard side, through skin fittings just above the waterline as there is a bulkhead between the cabins on that side that would allow me to run the hoses across the bulkhead, and therefore not across the walkway to the stern cabin.

Is there any reason to NOT do this that I should be aware of? It seems such a logical solution, but I am worried that I am missing something important, something to do with what might happen in various sea conditions or on the starboard tack or something. Maybe if I was on a starboard tack and healing heavily the cockpit would not drain, that might be a problem... albeit an unlikely one. And surely such a risk is lower than that posed by two extra skin fittings, maybe not. Any ideas?

I am reluctant to change anything without understanding the logic behind it.

Matt

P.S. The Swanson has a centre cockpit, with a raised stern, so the chance of a wave over the stern flooding the cockpit is pretty low, but of course, not impossible.
Our Celestial has the same setup as you describe. I had the same concerns about "excessive" through-hulls. Went though a similar thought process as are you. In the end, I kept them as installed. I couldn't get my mind around any result but problems when being on a stbd tack.

But what I also found - and your situation may differ:

Turns out, my big ol' manual last-gasp-last-chance bilge pump - located in the cockpit - exits through one (port side) of those cockpit drains. That same "drain" feeds into my water maker. The stbd "drain" also feeds the aft toilet. So I didn't/couldn't decommission those two "drains". Although... I did reroute the water maker input from port to stbd, as I thought bilge water could/might contain oil and that would play havoc with the water maker. (If I forgot to purge that tube after using the manual bilge pump.)
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Old 29-08-2013, 17:42   #28
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Re: Cockpit drains

I'm a skeptic when I read these things. A lot of work is involved, plugging two holes low in the boat is involved, longer hoses with possible vibration/wear points are installed. I'm just not one of those people with "fear of seacocks " I guess. You have a simple straight run now. leave it!
Remember, Murphy is alive and well..... If you eliminate all the seacocks in your boat but one... That is the one that will sink the boat!
I went thru the "seacock elimination" scheme years ago because some cruiser wrote it in a book and it sounded logical. Ireduced 12 seacocks down to about 7 or 8 as I remember. In the end I had a bunch of lengths of hoses, with a bunch of fittings/tees etc and hose clamps running through the boat. Frankly, in the end, I felt the boat was more likely to sink after I was done, and of couple of them didnt drain as well as they used to.
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Old 29-08-2013, 18:00   #29
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Re: Cockpit drains

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The drain height also has zero affect on water entering the cockpit via the drains. If the cockpit drain goes below sea level, water comes in.

Exactly.
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Old 29-08-2013, 18:06   #30
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Re: Cockpit drains

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Originally Posted by svmariane View Post
Our Celestial has the same setup as you describe. I had the same concerns about "excessive" through-hulls. Went though a similar thought process as are you. In the end, I kept them as installed. I couldn't get my mind around any result but problems when being on a stbd tack.

But what I also found - and your situation may differ:

Turns out, my big ol' manual last-gasp-last-chance bilge pump - located in the cockpit - exits through one (port side) of those cockpit drains. That same "drain" feeds into my water maker. The stbd "drain" also feeds the aft toilet. So I didn't/couldn't decommission those two "drains". Although... I did reroute the water maker input from port to stbd, as I thought bilge water could/might contain oil and that would play havoc with the water maker. (If I forgot to purge that tube after using the manual bilge pump.)
You describe a situation that I think my boat's original owner faced, so solved it by running separate skin fittings for all devices. Nothing was shared. It seemed odd when I first saw the setup, then thought about it and came up with the same sort of scenario you describe. I could even see why there were separate outlets for the main electric and main last chance pump only two inches apart, when I realised you could have a horror scenario of pumping frantically from one pump, straight back into the bilge through the other pump. So nothing will be shared on my setup for that reason and others.

Matt
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