Cockpit sole drains

[MattObjects]

The transom of my Grampian 26 has two holes through it to drain the cockpit sole. When I bought the boat, these were small, easily clogged, and lined with badly degraded brass tubing set directly in the plywood transom core. To ensure that the cockpit had adequate drainage in rough weather and to at lease prevent future leaks if not remedy prior damage, I cut slightly larger holes in the transom, filled the surrounding cored area with thickened epoxy, and fitted the holes with pvc pipe I'd cut and ground to be flush with the cockpit sole.

The new drains do not leak into the boat or the laminate core. However, once we were on the water last summer, we noticed two things: first, when using the outboard or sailing with more than two people in the cockpit, seawater came in the drains and would get everyone's feet wet. Second, there was a significant leak into the cockpit sole core from the top of the rudder shaft that necessitates re-coring the cockpit sole this spring.

As part of that project, I am debating whether to change the cockpit drain system.

I like the idea of drains mounted flush to the sole itself connected to a thru-hull below the water line. However, unless I close the seacock every time we use the outboard or have guests, that won't remedy the wet feet problem and will risk that I'll forget to open the seacock afterward and thus lose the benefit of the drains. It would seem better to just put flapper valves on the outside of the transom that will prevent backflow into the cockpit, but that is something I've never seen on a boat this large. Are there any reasons not to do that other than aesthetics? I'd appreciate hearing about any experiences others have had with drains through the transom. Thanks!

 

[wonkodsane]

I'd love to hear folks' take on this, too. My Sonic has the same issue.

 

[Ross]

They use such flaps on the exhaust for power boats. Also you can but back flow preventer check valves for larger pvc pipe ( 2") You can effectively glass the pvc pipe to the fiberglass of the boat with polyester resin. it will bond to the pvc epoxy will not bond to the pvc. My boat starts to flood the cockpit above 5.5 knots when powering. For the benefit of guests when that happens I casually remark that we seem to be sinking and throttle back a bit.

 

[Scott T-Bird]

I think you would probably find that flappers on the exterior of the transom won't work. I've seen them made in plastic and rubber. The plastic flappers, like a pair I have on the exhaust on my ski boat, will open and close at will depending on water movement. They do absolutely nothing to prevent water from backing-up thru the opening and have absolutely no purpose other than to cosmetically cover the exhaust when the boat is out of the water. The rubber flappers that I have seen are stiffer. They may provide some function when the boat is at rest, but when moving forward, they tend to open which seems to defeat your purpose since you say that water backs up when you are moving.

Actually, it seems odd to me that you should have this problem while moving. When you have a few people in your boat does it squat so much that your cockpit sole is below waterline? When you are moving, why wouldn't the water drain out like self-draining cockpits in small dinghys? The drains from our boat exit below the transom in the small area that sits above waterline but there must be at least a foot of freeboard to the cockpit sole, so the boat never squats that low or has water backing up into the cockpit. Why didn't you have this problem before you changed the drains if everything was essentially in the same position (only smaller drains)?

 

[MattObjects]

Scott, we obtained the boat last spring, after it had been sitting on jack stands for 7 years. I don't know what problems there may have been when the boat was in the water before that.

In the photos above, the bottom interior surface of the drain pipe is flush with top of the cockpit sole. The waterline is about 1/2" below the bottom of the bootstripe, so you can see from the picture that the cockpit sole is rather less than 12" above the waterline. Also, it seems to me that there is a sort of stern wave caused by the movement of the boat through the water that raises the water level directly below the transom above what it is elsewhere, though that may just be an illusion caused by the fact that the rear of the cockpit is lower in the water than the rest of it.

Raising the entire cockpit sole as part of the re-coring had occurred to me as a potential solution, but I discarded that option as it would require fabricating a new rudder with a longer post.

Given that I cannot redesign the boat altogether, the question becomes how best to handle the problem with the design I've got.

 

[sailingdog]

Why do you say that epoxy won't stick to PVC. That has not been my experience provided the PVC is properly prepped.

If you do glass in PVC pipe for the cockpit drains, make sure they exit above the waterline.

They use such flaps on the exhaust for power boats. Also you can but back flow preventer check valves for larger pvc pipe ( 2") You can effectively glass the pvc pipe to the fiberglass of the boat with polyester resin. it will bond to the pvc epoxy will not bond to the pvc. My boat starts to flood the cockpit above 5.5 knots when powering. For the benefit of guests when that happens I casually remark that we seem to be sinking and throttle back a bit.

 

[BobM]

How about a pair of expanding rubber plugs? Install them when you have company aboard. They are pretty easy to remove if you need to in a hurry.

Also, you could use an exhaust flapper, but need a check valve. Vetus sells a number of them (p. 70 of their catalog) with both flaps and butterfly valves http://vetusmarine.com/catalog.html but it will probably take a phone call to discuss which one might be suitable. It isn't clear whether they are somehow held closed or whether the mechanism is just gravity.

 

[Stu Jackson]

Your idea about running them vertically is akin to what we have on our boat. However, they do not exit below the static waterline, but on the curve of the hull near the transom, above the waterline. When heeled, one goes underwater. Sometimes one will back up into the cockpit when we're hard on the wind. The solution to that is to cross them under the sole. I haven't gotten around to that yet, but when it becomes time to replace the hoses from the cockpit drains to the thru hulls, I will do so.

 

[kenn]

Our little boat has a single cockpit drain that drains more or less vertically (gentle S bend) to a submerged thruhull on the hull bottom. The stock thruhull size was for 3/4" ID hose, but I found that the thruhulls' own holes would clog quickly, so like other owners i've increased this to 1" ID hose units. We never get water re-entering the cockpit via this drain - stationary, motoring or otherwise..

Why do you say that epoxy won't stick to PVC. That has not been my experience provided the PVC is properly prepped.

If you do glass in PVC pipe for the cockpit drains, make sure they exit above the waterline.

I don't think I'd entirely trust epoxied PVC. I'd either install plastic thruhulls as designed, or I'd use 4 SS nuts and bolts to bolt the flange of one to the underside of the floor, with a suitable gasket. And the right hose and hose-clamps.

 

[sailingdog]

I wasn't recommending merely epoxying the PVC in place, but glassing over the PVC. My point was that epoxy resin sticks to PVC pipe just fine... unlike what was said in the post I was responding to.

Our little boat has a single cockpit drain that drains more or less vertically (gentle S bend) to a submerged thruhull on the hull bottom. The stock thruhull size was for 3/4" ID hose, but I found that the thruhulls' own holes would clog quickly, so like other owners i've increased this to 1" ID hose units. We never get water re-entering the cockpit via this drain - stationary, motoring or otherwise..



I don't think I'd entirely trust epoxied PVC. I'd either install plastic thruhulls as designed, or I'd use 4 SS nuts and bolts to bolt the flange of one to the underside of the floor, with a suitable gasket. And the right hose and hose-clamps.

 

[Barnacle Bill]

Rigid PVC tubing is not recommended for cockpit "scuppers" or drains. It would be better to use something flexible that will not fracture if banged in to. You can also run the scupper tubes in a curve so that the curve is above the waterline which might prevent the back flow into your guest's toes. You can also run the port scupper from the cockpit sole to the starboard exit through hull and the starboard hose to the port exit through hull, which might aid you in accomplishing the run of the hose (loop).

 

[Manny]

When you enlarged them did you drill/cut using the center of the holes as a reference? If you did then is inadvertently made them too low. Could you build up the lower part of the holes back to the original level and then recut them making sure not to go lower than original? Otherwise maybe try shifting ballast forward, for example if your batteries are near the stern mount them forward. If your water tank is under the v-berth keep it full, etc, etc... This may all help with the sailing part of the issue but for motoring you may not have your outboard trimmed properly. You should have a pin to change the angle of tilt, maybe try adjusting it so the outboard isn't trying to force the bow up.

Manny

 

[Benny]

As Barnacle Bill points out pvc pipe is probably not the best choice for this project. By crisscrossing the conduits from port to starboard you will insure the drain openings are always above the water line at any degree of boat heel thus preventing back flow. In a boat where the distance from the sole of the cockpit to the waterline is minimal I would consider moving the through the hulls from the transom to the port and starboard undersides but keeping them, perhaps barely but, above the waterline at even keel. I would use quality through the hulls, hose and clamps to do the job.

 

[RichBone]

As for running with the outboard, try changing the tilt angle. Tilting the lower unit forward a bit might raise the stern enough to be above the waterline.

Rich

 

[MattObjects]

When you enlarged them did you drill/cut using the center of the holes as a reference?

Manny

The new holes were placed so that the lower interior surface of the pipe would be flush with the surface of the cockpit sole. Any higher, and water would collect behind them without being able to drain out.

I do plan to experiment with re-balancing the boat as we've got a smallish water tank under the v-berth competing with a large built in cooler, battery, and fuel tanks in the stern. I hadn't thought about adjusting the outboard trim (Duh!) so I really appreciate that idea.

 

[sinnettc]

FWIW, the scuppers in the transom of my Capri 22 are about 1/4 or 3/8" above the deck. Yes, a bit of water collects there but it's not much compared to a cockpit full. 8^D

I replaced mine last spring as one was damaged/leaking. I think they're inch and a half diameter.

http://www.catalinadirect.com/index.cfm?fuseaction=product.display&product_ID=536

 

[BobM]

This is pretty important

As for running with the outboard, try changing the tilt angle. Tilting the lower unit forward a bit might raise the stern enough to be above the waterline.

Rich

As Rich says, be sure your lower unit is perpendicular to the water. If it is tilted up even one setting it will just drive the stern down if you power up too much after hitting hull speed.