Cockpit drain pipes

[JeremyFowler]

Cockpit drain pipes – advice needed please… (Doing up an old 1975 Cavalier 39 Mk2)
The existing setup is 4 piddly pipes (about 25mm ID) running down to 4 draincocks. The problems are;
1) There are leak marks showing in the quarter berth from the inlets.
2) When we’ve had seas breaking in over the stern on our little trailer-sailer (our “previous” boat) it has drained very quickly through the outboard motor cut-out, I’d hate to think how long it would have taken through these little pipes. 2 waves and it would be into the companionway…
3) Too many holes in the hull that could potentially give problems at awkward moments.

I have to redo the floor of the cockpit in any case, so why not improve the situation. There is sufficient difference between cockpit floor height and waterline (about 300mm) to drain out above sea level.
My idea is to patch up the 4 holes at the bottom of the hull and make 2 larger holes, left and right, above the waterline in which larger rigid drain pipes are glassed in directly, not through stopcocks.
Yes, heeling would place the drain point on the “down” side below sea level, but should there be an issue with that hole leaking one could change tack to deal with the problem.

Should I use 50mm PVC piping? How do I join the end of the pipe to the hull where it exits the hull above the waterline? Simply glass the ends in firmly after making ridges in the piping to grip to the surrounding GRP fairing? I could strengthen the piping by glassing over it too, I suppose.

Any thoughts welcomed, especially from those that have dealt with this actual situation, ie PVC piping joining to the hull.

[Benz]

If I were doing that, I'd use fiberglass tubing. You can get it from McMaster Carr or other online suppliers. Then run each drain to the opposite side of the hull from where it starts, so you're not putting the cockpit outlet lower than the water when you heel.
You can make angled joints in FG tube by cutting an angle half what you want the turn to be and glassing the cuts together. This is how I did my standpipes for plumbing. With FG tube you have a good surface to glass to--PVC won't stick well enough to resin for my comfort.

[DefinitelyMe]

PVC won't bond very well. It will also go brittle and crack over time and has no give in it. I would glass a couple of bits of GRP pipe one at each end and join the two with good quality flexible hose, or use through-hull fittings, countersunk at the cockpit end. Be very sure that neither hole is below the waterline on any point of sail, or perhaps cross the hoses beneath the deck otherwise you'll end up with a wet cockpit all the time which would drive me crazy. I also think a rigid one-piece structure is not a good idea. Having said that:

I did make solid drain pipes for the deck drains on my boat. First I had the two holes, one at each end. I stuck a piece of flexible, soft-walled hose through the two holes to form the shape of the drains, then filled the hoses with fairly rigid 2-part polyurethane foam to set the hoses in that shape. I withdrew the hoses and used them as a mold for constructing fiberglass tubes, gelcoated on the inside. By leaving some soft hose sticking out of the end and clamping it in a vice I could remove the soft hose leaving just the glass tube. Stuck that through the holes in the boat and glassed into the hull at both ends, then cut off the excess and filled the depressions with gelcoat to blend in with the rest of the boat.

I'm very pleased with the result, but it is kind of an experiment. I have not yet been to sea with it like that, and I think that when I do there's a good chance some stress cracks might show up indicating a future failure. We shall see.........

[Manateeman]

Benz is correct. Please do not use pvc. You can make your own tube but it will cost you as much if not more. You might not have to crisscross the drains. Flaps on the transom maybe? Heel the boat over at the dock and you can see where the water line will end up. You can glass in a metal deck plate to keep your sneakers dry and take it out when off shore or high waves when you’ll have your boots on. You are trying to offload the weight of the sea not every drop.
Happy trails to you.
The manatee crew.

[Spot]

My cockpit has a 1/2" (13mm) deep sump where the inlet fitting sits for the drain. It runs along the entire aft width of the cockpit. If my boat and stern lazarette were bigger I'd try the criss-cross. Mine has a single 35mm with commercial fittings on each end with a sturdy flexible hose and hose clamps in between. Hoses only seem to last 30-40 years...

[alaskanviking]

I researched this extensively this winter before replacing my seacocks in March. I am positive I have read every forum discussion and post on this subject, and any professional reference I could get my hands on.

First regarding PVC for cockpit drains. I likewise was tempted. overall consensus is that this is dangerous to glass it or plumb it directly as the PVC is brittle and sensitive to UV light. IF you use a rubber flexible connection on each end it would be possible to use PVC however on most boats you would need one of those PVC heaters to make the pipe flexible and then the fittings required to convert to the short section of hose. it still is UV sensitive and will be exposed at the ends. only certain places have the correct hose fittings, using bronze hose barbs is expensive. there are better alternatives to PVC and ultimately my view was it was a long term risk with more expense and work on the install.

I seen fiberglass tube also suggested. it has similar issues. the hull flexes and the cockpit flexes so like PVC there is risk of cracking or fracturing the pipe. it is also UV sensitive however its stronger and it will take longer to degrade than PVC.

my ultimate solution was to get flexible PVC pipe, it fits schedule 40 PVC fittings. more on the vinyl side of the spectrum. don't get the marine stuff. they sell the exact same stuff as spa and pool or Pond hose. I found it on Amazon and several other venders under $1 a foot. its good for drains and the name brands have UV protectants in the makeup of the hose since its made to be outside with pools and ponds. the marine stuff even has the same brand markings, but its 3-4 times the price.

some other best practices
- ABYC has a formula for drain size. your cockpit area should be able to drain X amount of water in a minute and a half if it is fully filled. you may be able to get away with only 2 larger drains. calculate how many gallons in your cockpit and use the chart to figure out how big the drains should be.
- Having run outboard boats, you should verify your floatation back there is still good, check your seals/bedding on any inspection ports back there, check any of the wire/hose ports in the hull in the outboard well, and check the trim plane or transducer ports in the transom. I've had a couple of our outboard RHIB's come close to sinking because the bilge filled through bad inspection port seals while continually getting pooped with water. those outboards weigh a lot and combined with a full bilge can put you in a bad spot. transoms are prone to waterlogged plywood cores, which makes all these problems worse.
- if you have a sailboat than you may not need to change the position of the drains, if the boat is heeled the drains may be out of the water as designed.
- if you have a sailboat then criss cross your drains so they drain while heeled. However note that this depends on the design and doesn't work with all boats.
-most boats should have seacocks or valves for drains and bilge pumps, even if the outlet is above the waterline. depends on the size of the boat, design, and space available. some foam filled power boats cant really do this. the outlets may not always be above the waterline ie heeling/partial sinking, overweigh ect. You should have the ability to quickly shut a valve in case of a fuel spill ect. this is especially important on off shore vessels.

V/R

Robert