What are they?  Boats built to earlier ABYC or other standards might not have topside lockers separated from the internal areas of the boat, so for example water entering a sail locker can flow with gravity into the boat's bilge.  There may also have been no intent by the builder to bring all edges of a lid and its opening together, an example of this in the case of WHOOSH is that the coamings of her sail lockers were intentionally built not to match up with the undersides of the cockpit locker lids on all four sides.  This allowed the locker opening to be larger and accept the passage of bigger items.  In such a case, the unsealed/unsealable lockers can permit even more seawater into the interior of the boat, a casualty typically referred to as down flooding.  To prevent this from happening, one can consider building down flooding boards to cover & fully seal the locker openings.  Normally, these aren't used until needed - e.g. the pending arrival of a storm or perhaps steeply pitched, sloppy seas that are coming aboard - at which point they can be rigged underneath the existing locker lids.

One Approach:  We didn't get to this project before crossing the Atlantic in 2003 nor did we tackle it before crossing Biscay in 2005, but we did want to complete it before leaving Europe for the Canaries and the onward Atlantic Crossing to the Caribbean.  It turned out to be quick, easy and inexpensive to do.  What was missing was my ability to identify a simple solution.  I finally concocted an approach, visited a Spanish DIY store while in Almerimar, Spain and the work was done in a day for less than 50 Euros.

The picture (left) pretty much tells the tale.  I first applied polyester resin to all the cut wood sections as only low-grade ply was available.  I installed two #8 machine screws, locked in place with nuts on each side, on each of a locker's four sides, the machine screw heads to serve as the anchor points for bungee cord loops threaded and knotted onto the boards.  I added cleats on each board's underside so they would simply fall into their respective openings and not slide around, after which the shock cord is looped over the screw heads.  Keep in mind that, when these are rigged, the regular GRP locker lids are closed and secured, with the down flooding boards secured underneath, so a heavy sea breaking aboard slams into the GRP lid and its the momentary sluicing of the seawater around the cockpit that the board is attempting to defeat from entering below.

I had planned to place rubber strips on all four edges of each board but initially couldn't find suitable rubber.  Once they were finished, the fit was so flush that I wasn't convinced this step would make a good deal of difference in the amount of water getting below...altho' it no doubt would be the 'right thing to do'.   Several years later, several folks on the SSCA Discussion Board asked about these boards, so I thought I'd add them to WHOOSH's new Pacific prep section as we would certainly not want to consider heading out there without a way to prevent down flooding.