Self-Draining Cockpits

by Mike Waters NA

The following article was received form naval architect Mike Waters, in response to a previous article we published on the topic. —Eds

I have enjoyed Glen-L designs since way back in the 1950s when I started designing small boats myself, so I feel somewhat sheepish to criticize this re-run of a Glen-L  article on “how small boats cannot have a self draining cockpit.” Really?..... sorry guys, but this hits me as misguided hogwash and should be challenged … which is the reason I am writing.

Although I spent 40 years designing ships in the 100-600ft range, I also designed a quiver of small boats from 7ft to 32ft for friends and my personal pleasure, and at least 75% of these had self-draining cockpits! In fact, on my website, I rather boldly say that ALL small cruising boats should have a self draining cockpit, as getting swamped and capsizing is just too risky with all the gear one needs to have on board … and the risks can be significantly lowered with a little self-draining help. For several years,  I used to dinghy cruise along the south coast of the UK as a teenager, so I know what getting swamped and capsizing involves as I survived through it ... but sometimes only just! I definitely used “a couple of my cat lives” with one near death experience that perhaps explains my passion about this.

First, this claim of needing 9” is just not backed by fact. It sounds like the writer thinks that the higher it is, the more head there is to drain faster. Just not fact. The effective drainage head is the height of water above the cockpit floor, not above the waterline, so if the floor is 9” above the waterline or 2” above the waterline, the drainage rate is theoretically the same, unless the floor is pushed below the water level due to added weight, trim or heel.  Sure, it’s true that a low floor will indeed flood in if the weight inside moves aft to push the drain outlet(s) under, but that is a temporary status that can be easily corrected as long as the floor is above the waterline in the designed and sailing position.

I have used at least partial cockpit self-draining floors in boats as small as 12ft and my 13.3ft Flying Junior shown here had a practical full length one.  My son and I cruised that boat DRY for several years, while my daughter and an overconfident boyfriend managed to capsize it.  But it was righted and sailed home without losing anything and never needed a bailer on board.  Often one can build in a partial floor above the waterline .. just 2” above the loaded waterline will work, though 3” is better at the forward end.   The rest of the boat can be designed with a well fitted with a self bailer … the whole idea being to keep the free surface and the entrapped water, as low as possible.

By the way, in the text, the author refers to PPI which is the parallel sinkage in Pounds Per Inch, but then goes on to quote a trimming moment in Lbs Ft.  That is the MCT . the Mt to Change Trim and NOT the PPI, so this might confuse some readers.   The point made re moving aft and water entering is correct though, but as I said, it’s temporary just while the person needs to be aft. Of course, each boat design and operational needs will decide how low the self-draining floor can be but for some dinghies, you have to push the limit as the total depth is not high.  But even the lovely Paper Jet 14 design by Dudley (Dix) featured recently by SCA, has a full length draining floor.  Boats set up to dinghy cruise (like my Flying Junior) can have large transom flaps with soft seals, held shut with shock-cord. They are normally pretty watertight when weight is needed aft but as soon as one starts sailing in weather that throws spray aboard, one simply releases the cord to the flaps and out shoots any water.  At the after end, the floor actually only needs to be ½” above the loaded waterline for this to work.  With more boat depth forward, there is no problem to have the floor 3” or 4” above the waterline, so that even when camping aboard and rain might get in, there is a natural drain to the rear that keeps the floor free of all solid water.  So yes, ask your designer to consider this.  If he/she knows their stuff, they will do a few calculations to make sure that there is also some underdeck foam or other buoyancy at the rail (or mast head), to make sure a boat with a buoyant floor does not turn turtle on you. Even in boats as short as 10ft, one can build in side buoyancy so that even when capsized, the cockpit space is still self draining. My last design built at 87 does that .. and most certainly my W17 trimaran design before that has a full self-draining floor as well as every other trimaran I have designed. Yes, it’s low enough to flood a little when one moves far aft with the boat stationary, but quickly drains when you move forward. When sailing, the dynamic lift more than makes up for the aft weight transfer and even with two adults way back aft, the cockpit then still drains.    And true, I do not ever need a bailer on board!  Of course, the drainage openings need to be fairly large and fitted with deflectors to help suck the water out, then working rather like self bailers … but it’s all very doable and well worth the added safety it gives.

If you cannot afford to lose the storage space under the floorboards (always wet anyway), then add some quasi watertight covers for access. But when you have that higher-risk open sea trip to make in a good breeze, don’t hesitate to throw down the duct tape over the hatch joint. Just remove it on arrival so that it does not leave a gummy residue.

And if you are short of space but still want a self-draining boat, build yourself a small but seaworthy trimaran that offers fantastic comfort, safety, speed and space for cruising .., all must things that the older small-boat sailor will appreciate. I plan to cruise mine into my 90s and so now do many others. I promise you will discover a world you did not know existed!

Here’s to happy sailing and safer cruising—Mike Waters www.smalltridesign.com •SCA•