Cockpit Scuppers Size and Hose material

[zboss]

As you all know, I am switching out my thru hulls. I am thinking about increasing the size of my cockpit scuppers... I didn't measure them but they appear to be a large diameter hose.

I had them closed when it rained this week and when I went to dump the cockpit it seemed to take quite a while to completely empty, which got me to thinking that maybe they should be emptying faster in case of getting swamped.

What are the ABYC standards on hose sizes for the cockpit? What materials should they be made of... the ones I have now appear to be engine hose but they bend at a funny angle and where the bends have occurred, there was some definite cracking of the hose material.

Any experience in this regard that you guys could impart is appreciated.

- z

[GordMay]

Excerpted from ABYC H-4 ~ Cockpits and Scuppers:

4.5.9.1
When filled with water to the fixed sill height, and with weathertight hatches sealed to the height of the sill, 75% of the cockpit water volume shall drain in 90 seconds. There shall be no leakage to the hull interior during the test.

4.5.9.2
The minimum requirements for the drainage system shall be calculated using either of the following formulas:

4.5.9.2.1
A = 0.385 x (Vc ÷ Root h)
where
A = minimum total area of all drains - square inches
Vc = total amount of water that can be contained in cockpit with the drains closed - cubic inches
h = cockpit depth - feet

or

4.5.9.2.2
Dn = 0.7 x [Vc ÷ (n x root h)]
where
Dn = minimum diameter of each drain, in inches
Vc = total amount of water that can be contained in cockpit with the drains closed, in cubic feet
h = cockpit depth - feet
n = number of drains in cockpit

ABYC H-4, Cockpit Drainage Systems

Here ➥ ftp://64.197.117.239/Public/Software...ndards/H-4.pdf

Or ➥ ftp://64.197.117.239/Public/Software...s/2007/H-4.pdf

[SVTatia]

Originally Posted by zboss

As you all know, I am switching out my thru hulls. I am thinking about increasing the size of my cockpit scuppers...

If you increase the the hose size you would also have to increase the thru-hull and seacock - to enlarge an existing hole is tricky but easily done.

[zboss]

Thanks! I'm still learning the best way to read through the ABYC documents!

[roverhi]

1 1/2" drains are the absolute minimum and probably not adequate for a typical sized cockpit despite a pair of them being standard on almost all boats. The small footwell on the Westrsail 32 seemed to take forever to drain with two 1 1/2" drains. Can't imagine how long a six foot or longer cockpit would take to drain. Have added a second set of 1 1/2" drains on my overly large cockpit.

[SecondBase]

Bigger drains and/or smaller cockpits. Small cockpit = seaworthy. Just don't try to find that thought at the boat show these days!

Open transoms do solve the drainage problem.

For closed transoms - Simple rule of thumb- if the cockpit is longer than 6 times the cleat length she's blue water iffy. Easy walk-by screenings at the boat show. No need to step aboard.

6 Times the Cleat Length

I didn't say not blue water - just iffy given design insight from the rule of 6. The mindset that specified the cleats also choose the drainage system.

[Cheechako]

Most boats have two 1.5 drains. Some have four. They do drain real slow for sure. It's a big trade off putting huge seacocks and hose and fittings in. Easier I think to add a big drain or two from the rear of the cockpit out the stern if you are worried about it, maybe a couple 3" diameter with exhaust outlet fittings and exhaust style flappers on the stern.
I think most boats would be little effected by a full cockpit of water for the time it takes to drain in reasonable weather, but of course when your cockpit fills you might be in storm conditions. Lets say you add a bunch of stuff to reduce the time to 1 minute to drain.... will that be enough if the huge wave period is less than that? will you still have control problems when the next wave overtakes you? If the wave period is filling your cockpit every minute or so, does rapid draining help?
Time might best be spent avoiding storms or buying a boat with alot of stern bouyancy.
another thought: A modern boat with large cockpit, and broad stern sections carried well aft, might be more seaworthy in this respect than an old style with a narrow stern, overhang and little reserve bouyancy.

[Watercolor]

Gordon,

What does the ABYC define the "sill" as? The lowest drainage point?

Thanks

[JPA Cate]

I'm thinking the "sill" is the height of the cockpit seats, or the height of the bridge deck if they are not the same, but someone else may know more exactly.

[MarkSF]

Originally Posted by SecondBase

Bigger drains and/or smaller cockpits. Small cockpit = seaworthy. Just don't try to find that thought at the boat show these days!

Open transoms do solve the drainage problem.

For closed transoms - Simple rule of thumb- if the cockpit is longer than 6 times the cleat length she's blue water iffy. Easy walk-by screenings at the boat show. No need to step aboard.

6 Times the Cleat Length

I didn't say not blue water - just iffy given design insight from the rule of 6. The mindset that specified the cleats also choose the drainage system.

Insufficient information. Which cleat length? What is that? My jib sheet cleats are about 5" long, so the cockpit can only be 30"?

[NahanniV]

When you are buying your thruhulls, valves, and adapters you need to check if they are full flow i.e. the bore of all the components is the nominal size and the hose size will need to be larger.

Many valves and seacocks are not full flow, some are quite a bit smaller.

The flow out the cockpit drain will be limited by the smallest bore component.

[zboss]

The one thing I noted on my Cabo Rico is that once the well of the cockpit fills up, there is only one place for water to go if not down the drain - into the companionway. Not that you would have the companionway open during rough weather but you would think there would be a deck level drain.

[Watercolor]

NahanniV comment reminded me of the fact that, if your trying to up the thru-hull/seacock size inexpensively, the Forespar 93 series is definitely not the way to go. The 3/4", 1 1/4" and 2" Forespar 93 thru-hulls are not full flow. In fact, they're ID is the same as the size below them. For example, the 2" thru-hull has the same ID as the 1 1/2" Forespar 93 thru-hull. And the Forespar 93 2" thru-hull has about a fifth less Id than a conventional thru-hull.

[Noreastern]

Here is another angle on thru hull cockpit drains. We have forward cockpit drains that are 1" that drain thru two taper valves below the waterline. In a effort to decrease thru hulls in our planned refit we are thinking that maybe we could lead the hoses above the waterline with a cowl shield attached to the topside above the waterline. Disadvantage would be a need to screen hole to keep rodents from crawling in.

[SabreKai]

My cockpit scares the bejeebers out of me. I measure it, and calculated something like 64 cubic feet of water. I have two piddly 1.5 inch drains. I am currently investigating the possibility of installing two large flow through ports, (my boat is steel) by welding large bore pipe in. My set up as it is is scary. galvanized pipe sections, old plastic tube and industrial gate valves. gotta go.