Self-draining cockpit floor height

[Steven R]

Is there a generally accepted minimum floor height (above lwl) for a self-draining cockpit? This would be for an 18' daysailer

Steven

[Ian McColgin]

Because sailboats heel over, most cockpit drains in small boats let in lots of water unless they have a floating check valve or are of the elvstrom type that make use of a venturi.

Given that reality, the height does not really matter too much so long as it's at least a few inches above the waterline when normal to heavy crew are aboard.

I know of a day sailor where this was done poorly.

She's a Cape Dory Typhoon of the rare day model - no cabin and very large, like going forward of the mast - cockpit. Originally she had a pretty deep cockpit sole, not self-bailing. There was safety in that stern and bow were bulkheaded to provide enough air to keep her afloat in the incredibly unlikely event of swamping.

Some owner did not like bailing after a rain and did not like fussing with a cover, so he had a higher sole installed. Regretably it pitched aft with drains at the front so it tended to puddle at rest. The drains in front were good when heeled underweigh.

When the boat was on the mooring, the puddling was a pain as if the boat was not sailed for a few days and the sun came out, it made an algae bloom. To correct this he added drains aft. Unfortunatly, these are low enough that as soon as one person my size (250#) boards the boat, it's underwater. It's too close to the waterline for a floating checkvalve to work. under sail the leeward aft drain lets in even more water.

Part of the problem is that the fore drains are correctly crossed but the aft are not.

So, as you can see, there are a number of things to think over.

For a day sailor, I'd try to pitch and curve the cockpit sole to make the lowest part an inch or three above the water and right at the place of maximum puddling when heeled and underweigh. Put an elvstrom just there on each side. Remember to shut them when you plan to stop.

G'luck

[JimConlin]

For a boat that heels, making the cockpit sole narrower increases the distance of the low corner of the cockpit above the water. Watertight seat risers add complication in the building.

[PVanderwaart]

Is there a generally accepted minimum floor height (above lwl) for a self-draining cockpit?

Four inches. I don't remember where I got that number, but there it is. Lots of boats under 18' have less, I'm sure. I had a boat where it was about 1/4", and the heave of the boat would pump water into the cockpit under some conditions. I invested in a rubber plug.

[Jonas]

Ian, what's an "elvstrom"?

[Gavin Atkin]

Eight inches. It comes from various sources, but the one I remember is Des Sleightholme.

Gavin

[Alan D. Hyde]

An "Elvstrom" is a patent self-bailer, invented by a well-known dinghy-racing sailor.*

Here's a photo; I'll look for a better one---

http://www.windmillclass.org/rigging/t_bailer.jpg

Here's a better view---

http://www.westmarine.com/images/full/23003_f.jpg

BTW, the bottom of the cockpit is not the "floor."

I'd call it the well, but that's one of several terms that could equally well be used...

Alan

* No one has come close to matching Paul Elvström's four successive Olympic Gold medals and 14 world championship titles. Now the 72-year-old has just taken delivery of a new Finn...

[ 08-30-2005, 02:52 PM: Message edited by: Alan D. Hyde ]

[peb]

I have a boat with low free board and the result is that the cockpit sole is only about 3 inches above the waterline. I wanted a self-draining cockpit and was really worried about this working. I have a drain, without a flowting check valve, set in the middle (on the centerline) of the sole. I do not have any problem with water coming in through the drain when the boat heels. Of course, if water is in the cockpit from over the boat, I have some standing water along the sides when the boat is heeling, but with the grating being an 1.5 inches higher than the sole, it is never enough to really get your feet wet.

The only problem is it has to drain to a thru-hull below the waterline, which I have never liked. You have to leave the seacock open to drain rain water, but then you are at risk to sinking based on a simple hose failure. I do go off and leave the boat with that drain open when I expect rain, but not for very long and I keep a very close eye on that hose and its four clamps!!!

I did try a drain with a floating check valve, but found that it significantly slowed down the rate at which water drained and wasn't really helpful.

[ 08-30-2005, 04:17 PM: Message edited by: peb ]

[Gary E]

For sucha a small boat you sure are making it complicated...

Carry a buckett and a sponge...

[Steven R]

Thanks for your replies, everyone.

The reason I was considering a self-draining cockpit is that the design would not have seats or thwarts and the crew would be sitting on the sole (as in a Beetle Cat or a Boothbay Harbor one Design).

[Hwyl]

Elvstrom bailers are now (and have for years) been called Anderson bailers. The don't cause a cockpit to be self bailing.

For what you are describing take a serious look at the JY 15.

http://www.shakealegmiami.org/osc/images/jy-15-sailboat.jpg

She has a false bottom that you sit on and holes in the transom to bail. The disadvatage is that the cockpit sole, tends to be a bit of a skating rink (she's rotomoulded plastic).
Something else to think about, they are pigs to right when turtled, because the bouyancy is so low (ending up being high).

Good concept though and both those faults can be easily remedied.

[ 08-30-2005, 08:06 PM: Message edited by: Hwyl ]

[Steven R]

Hwyl,

This is along the lines of what I was thinking. Regarding buoyancy, since you mention it, I'm envisioning airtight storage compartments under the sizable aft deck, forward deck and for about 4' laterally centered under the approx. 10" wide side decks.

Steven

[Hwyl]

That should work, are you thinking of glassing tubes through the aft bouyancy for drainage.

There wa s a boat, International Tempest (not the horrible O Day one) that had a false bottom and elvstrom anderson bailers set in sumps, so the boat would drai and auto bail (a little faster) or you could close the bailers and have a smooth bottom.

[Venchka]

If you read the Atkins' plans, they have cockpit soles from 4" to 9" above LWL.

Wayne
Around somrplace. :D

[ 08-31-2005, 12:05 AM: Message edited by: Venchka ]

[Jay Greer]

One method of keeping water from backing up on a lee side cockpit drain is to cross the drains under deck.
This will, of course leave a lot of water sloshing about if you take a greenie while laid hard over.

So, here is an alternative that will not allow water to back up from the lee drain. Make a flapper cover of thick drafting mylar vellum and staple it to the hull forward of the through hull fitting. Fair the leading edge with a ramp of epoxy and micro balloons and paint the flap and ramp with bottom paint. This really works and is both simple and cheap to make. When the weight of water in the cockpit over comes the outer pressure on the flap, it will allow the cockpit to drain.

[bainbridgeisland]

What is the purpose of the self-bailing cockpit, to recover from a capsize, empty the cockpit of waves and spray or expel accumulated rainwater. The cockpit would be designed differently for each of these needs.

If water comes into the cockpit, your butt will get wet self-bailing or not. Also, raised sole cockpits are uncomfortable to sit on when put in small boats so be sure you are using the right reason for doing it. You would be surprised how comfortable a normal thwart is compared to a double bottom.

If your boat has positive buoyancy and the centerboard trunk is not too low you will be able to recover from capsize. Even a bailing bucket will do the job. Side deck buoyancy chambers keep most of the water out when a boat is on its side. Anderson bailers will take care of the rest in a few minutes if the boat is moving 2-3 knots. A bailing bucket, sponge or Anderson bailer will take care of spray too.

A spray deflector on the foredeck (coaming) will help a lot with splashes and spray.

A foot well with a tonneau cover over it will do a good job with rainwater. These can be very comfortable. Imagine seats or deck all around and a low place to put your feet too. Just snap the cover on when you leave the boat.

Double bottoms that drain aft on non-planing boats will usually fill the cockpit with water in some conditions if not fitted with good transom doors (flaps). The stern wave can often be 8" high or more on heavy boats. This would submerge a cockpit that was lower than 8".

The raised sole in my 24' midget ocean racer was 15" above the waterline and 24" wide. It emptied out the open transom. After 15,000 miles offshore we took water into it only a few times. Usually even 10' breaking waves didn't fill the cockpit. So it is possible to get a cockpit high enough.

If you insist on a self-bailing sole and you can't get it high enough to drain out the transom, drain it amidships (i.e. half way between bow and stern) and keep it narrow. 5" above full load waterline is enough for most small boats as mentioned before. Be sure the drains are big enough.

[Steven R]

I appreciate everyone's feedback. At this stage, the design is just vapor floating around in my cerebrum, with a couple of "envelope sketches".

Hwyl wrote: are you thinking of glassing tubes through the aft bouyancy for drainage My orginal thought was to cross a couple of drains at amidships

Jay Greer wrote: Make a flapper cover of thick drafting mylar vellum and staple it to the hull forward of the through hull fitting. Jay, thanks for that idea. I like the simplicity of it.

Gray E wrote: For sucha a small boat you sure are making it complicated...
Probably ;) To be honest, I wasn't completely sold on the idea to begin with. I'm just weighing options. After reading all of your responses, I'm inclined to think that it's more trouble than it's worth.

BainbridgeIsland wrote: What is the purpose of the self-bailing cockpit, to recover from a capsize, empty the cockpit of waves and spray or expel accumulated rainwater Like most, I want it all and don't want to have to give up anything ;) Ok.... realistically, this design would be for my personal use and would spend most of it's time on a trailer when not actually being used. So, it's not an issue of it sinking at a mooring. While it would be great to minimize the need to bail after a capsize, I don't envision this design serving that purpose. The desire is primarily for comfort, while underway. As mentioned above, I'm just exploring options and I'm not sold on a self-draining cockpit. I'm more inclined to believe that floorboards raised high enough would handle the comfort issue even more effectively.

Again, thanks for all the feedback. Even though I am leaning away from self-draining, keep the feedback coming. I'm learning some things here.

Steven