Cockpit Drains

[Graham_Wright]

There is a conflict between the desirability of having them as big as possible and finding space for the through-hulls. Any opinions on how big they should be please? Mine is a centre cockpit high freeboard (Colvic Countess 33). Presumbably lots of water in the cockpit is bad news for stability. There are four obvious drain positions in the cockpit corners.

Also, is it preferable to use rigid piping (grp or 316) between the drain and the outlet or flexi tube? In the former case, there seems to be no reason for sea cocks. In the latter the sea cock presumably helps to combat problems with the flexi tube; – but then the sea cock fails!?

Thanks in anticipation

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[AndrewB]

RCD regulations (ISO 11812) specify cockpit drain size in terms of the speed which they will empty the cockpit from completely full (overflowing the scuppers). This varies with cockpit size and RCD category, but as a rule of thumb the cockpit should be drained in 3 minutes. See for example <A target="_blank" HREF=http://"http://www.ibinews.com/ibinews/ebb/tech_9.html">HERE</A>.

My guess from what I remember of a Colvic Countess is that two drains of minimum diameter 40mm (1½") would be sufficient.

Cockpit drains normally incorporate a flexible component as otherwise they could easily become stress points as the yacht works, obviously not a good idea specially at the lower end! In any case a straight lead is often not practical, and there are some advantages in crossing-over the pipes so that the port drain leads to the starboard outlet and vice versa. Seacocks should be fitted.

 

[dickh]

The usual size 1½" diameter bore hose. Depending on where the exit point is depends on wether you fit seacocks or not. If exiting below the waterline then seacocks are a must - if above the waterline then probably not necessary. Flexible tubing is usually used, as it is flexible and can go where rigid pipes can't! Make sure it has a definite 'fall' so no water can accumulate in loops etc.
My cockpit drains directly into the lazarette which then drains overboard thro' the transom, thro' a central hole - not an ideal system and one day I'll change it to proper hoses draining overboard thro individual drains.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[steelfloats]

Having had a number of full cockpits when crossing the Atlantic due to slow emptying, my own boat has 1 (one) 6" cockpit drain, it empties really fast; it does not have a sea cock. The lower end comes up above the water line, with thick (oilfield!!) PVC pipe for the junction. Size is important, the larger diameter the better (in my opinion!)

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[Graham_Wright]

Yes;- point taken on stress. I thought of putting a short length of flexible well above the waterline to take account of movement of the cockpit relative to the hull.
The concensus seems to be for the seacocks so far!

<hr width=100% size=1>GBW

 

[Bodach na mara]

In my last boat (an Angus Primrose designed Commando) the drains were formed as trunkings br screwing plywood strips on spacers to the bulkheads, hence things like mini centreboard slots with no seacocks. There was an article years ago in PBO suggesting a similar idea for GRP boats. The benefits are that the drain is part of the structure and there is no seacock to leak or maintain. The only drawback it the need for (and difficulty of) antifouling the inside of the drains.

Actually, it often causes me a loss of sleep thinking that, for the most part, my bilge is seperated from the sea by 15+mm of GRP, but from the 1 1/4 inch seacocks up to water level there is only 2mm of plastic.

<hr width=100% size=1>Ken Johnson

 

[RupertW]

Cockpit draining is one of the few areas where the modern AWBs have increased safety and reliability as a by-product of a bit of boat-show sales nonsense. By having a walk-through stern to the unfeasibly often-used swimming platform, you have a cockpit with a whacking great hole in the back. It feels nice and racy as well.

Water can pour out hundreds (thousands?) of times faster than even big-bore cockpit drains and there are no pipes to become detached and no need for sea-cocks. Never heard of anyone retro-fitting a walkthrough stern - probably a very unwise thing to do.

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[halcyon]

Two 4 inch pipes from cockpit, through lazzerette and out the transom, no seacocks, no problem.

Brian

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[oldsaltoz]

G'day Graham,

If possible / practical, keep the outlets above the waterline, far less to worry about with fewer holes in the hull below the waterline.

To maintain the required fall and flexibility, consider a short length 96 inches is fine) of flexible hose at each end of a fixed PVC pipe.

Also note: most cockpits have mouldings with provision for 4 outlets not because they are essential, but because some drain forward and some aft, so most only ever have two plumbed.

PVC can be difficult to glass, but if you heat it with a hot flame so that very small dark beads form, you will find glass will take to it, the flame must be very hot and it only takes seconds for the beads to form.

Hope this helps.

Avagoodweekend........



<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[Graham_Wright]

I guess it can probably pour in at the same sort of rate!
Never did fancy those missing stern jobbies


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[Graham_Wright]

With a stern cabin we have a problem with access. Wife might object to a couple of 4" pipes down the middle of the berth!

<hr width=100% size=1>GBW

 

[Graham_Wright]

Not sure how much freeboard your boat has, but 96" =8' is a bit out of my league (or did you miss the shift key?!)

Great point about the fall. My cockpit sole falls forwards and it is possible to route the two fwd drains athwartships above the waterline.

My fear with flexible plastic piping is that with an engine fire, they would melt and we would have a bonus problem. (I guess that would extinguish the fire though!)

I'm feeling inclined to stick with the two stainless tubes for the after end (fwd fall can become sternward fall in the sort of sea which invites itelf aboard), around 1 1/2" diameter solid through the hull but connected via 6" of flexi just below the cockpit.

Thanks ffor provoking advice

<hr width=100% size=1>GBW

 

[paulskent]

Somebody put me out of my misery and tell me what AWB stands for ???

Can't find a reference anywhere..

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[steve_l]

Average White Boat )

-steve-

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[paulskent]

I take it this is intended as a "put down" of some sort pointed at the mass produced benjenbav type cruisers ??

Shame really becase the Average White Band are one of may all time favourites..

I always wanted to be their bass player...

Pick up the pieces !!!!

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[AndrewB]

Effect of engine fire on cockpit drains.

The possibility of the cockpit drain hoses melting in a fire is an issue for most centre cockpit yachts where the drains are likely to be close to the engine.

With a GRP or wooden boat and a serious fire, then water coming through the cockpit drains is the least of your worries. However, with a steel boat, or a minor fire in a GRP/wooden boat, water coming in as a result of the drain hoses melting could be the last straw. I've replaced the plastic hose on mine with reinforced exhaust hose wrapped in fire-retardant material to give it more chance if that happens.

If, even so, the hoses disintegrate, in theory the holes could be bunged well before the boat sinks. Unfortunately in practice there may be too much smoke, and too much danger, to permit access to do so. Haven't worked out how do deal with this last.

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[snowleopard]

did that on a racing dinghy and it worked very well - a length of 4" drain pipe wrapped in GRP. used a plastic funnel as a non-return valve with a bit of light bungy to hold it in place. very practical but not the most elegant solution and the funnel needed replacing every year or two because of UV degradation.

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