Underdeck Hatch Hold-downs
(from Newfound Woodworks Strip Building News Fall 99)

After spending hundreds of hours building a kayak you may be averse to disturbing the lines of your wood deck with excess hardware.  You can reduce some of that clutter by using an alternative mechanism for securing your hatch covers.  Underdeck bungees require no external hardware that would detract from the look of your boat, yet they provide a secure grip on the hatch covers.  In fact, the tension on underdeck bungees can provide a greater downward force on the hatch cover (and therefore a better seal) than externally mounted bungees.

There are undoubtedly a number of ways to use underdeck bungees to secure the hatch cover, but I'll describe a couple configurations that I've used that have been successful.   Whether you have raised or flush hatches, you can adapt one of the methods to suit your needs.

Construction

The arrangement that will work for most kayaks is one in which each bungee is attached to two points on the hull below the sheer line. Each bungee stretches from the anchor point up to a hook on the underside of the hatch cover.   You can use a block of wood to form the anchor points, but I used two slices of ½” PVC tubing because it’s strong and light. Locate the loops of PVC near the corners of the hatch opening and at a depth that will allow the bungee to provide sufficient downward force on the cover.  Make sure that they’re not so low that the bungees would interfere with gear that will be placed in the hatch later.  For the flush hatches on my Guillemot, I placed the loops about 2 inches below the sheer line, but you should tailor the placement to your own boat, hatch placement and hatch size.   Attach each of the loops to the hull with thickened epoxy and reinforce it with a strip of bias-cut fiberglass over the loop and onto the hull with about an inch of overlap.  If you do this before the deck and hull halves are attached, it will be easier to clamp the loops.  However, if you haven’t cut the hatch openings and you’re unsure of where they’ll be located, you can attach the loops later.

On the hatch cover I mounted two inward facing hooks positioned about two inches in from the edge and centered between the PVC loops on the hull.  Moving the hooks in from the edge helps to distribute the downward force over the surface of the cover, but again, you don’t want to move them so far in that the bungees interfere with gear that will be stored in the hatch. Also, you don’t want to have to reach too far underneath to unhook the bungees when you want to remove the cover.  To create the hooks, use a holesaw to cut a disk from a piece of hardwood (I used maple and a 1 ½” holesaw) and then slice it in half to form two semi-circles.  To form the lip of the hook, use a ½” forstner bit or brad-point bit to drill an off-center hole that encompasses the pilot-hole left from the hole saw.  Trim off the weak edge of the hook and round over the edge.  Set the hook on a flat surface and make certain there is enough clearance for the bungee, and trim the hook if necessary.  When cutting the disk in half, cut it along the grain.   This will orient the grain so that the lip will be as strong as possible.   Epoxy the hook to the hatch cover, and run a strip of glass over it.  After all epoxy is cured, sand the loops and hooks to remove any sharp glass edges that could wear through the bungees.

If you have flush hatches, you’ll need a way to lift up the edge of the cover allow you to disengage the bungees underneath.   A simple way to do this is to form a finger divot on the deck of the boat.  If you locate the divot at the low point of the hatch opening, it will also serve as a perimeter drain.  You can put one on each side of the hatch opening, but I use only one.  To form the divot, take a 4” section of that same piece of ½” PVC pipe, wrap it with some 80 grit sandpaper, pick your starting point, and start sanding.   It will take only a couple minutes to create a suitable divot.  Give it a good coat or two of epoxy.  If you have raised hatches, the edge may provide enough of a grip to allow you to lift it.  If not, put a divot on the deck or on the edge of the hatch cover.

Now that you’re certain you’ll be able to lift the hatch cover once it’s attached, you can fit the bungees.   Thread a length of 1/4” bungee through the loops for one of the hold-downs and put a generous knot in one end (I used a figure-8 knot).  Make sure the knot is big enough so that the bungee won’t pull through the PVC anchor.  Pull up a loop in the center and tie a loose knot in the other end, and fit the hatch cover, slipping the bungee loop over the hook.  Adjust the loop length to get the tension at a comfortable level.  Remember that you only need a firm grip, not a death grip.   Once you’re satisfied with one side, tie a permanent knot and then setup the other bungee.  Try to equalize the size of both loops so that the cover will naturally remain centered.

Variation 1

If your kayak has a peaked deck or if you have raised hatch covers, you may be able to orient the bungees across the centerline at the fore and aft edges of the hatch opening.  This method has the benefit of taking-up less space internally because the bungees are  anchored to the underside of the deck instead of the hull.  However, the bungees attach to hooks that are mounted along the centerline of the cover, so the downward force is not distributed as well as the other orientation.   Use the same technique for creating the anchor points and hooks, but mount the anchors on the underside of the deck equidistant from the centerline and at a position that the bungee angle will provide sufficient downward tension.  Position the loops fore/aft so that looking straight down on the opening at the centerline the bungee should just be visible.  This will ensure that there is a fore/aft angle on the bungee to give it a good grip on the hook. Mount the inward-facing hook to the centerline of the hatch cover an inch or so from the opening.

Variation 2

If the angle of the bungee from the anchor to the hook does not provide sufficient tension, or if you want to more evenly distribute the force on the cover, use two hooks per side.  This will be a little more difficult to remove, but will likely provide a better seal.

Final Notes

To remove the hatch, lift an edge of the cover with one hand, and reach under with the other hand and push the bungee off the hook. With one side off, you can rotate the cover around other bungee “hinge”, expose the hook, and detach the second bungee.

Whatever method you choose for hatch hold-downs (and this goes for external methods too), it’s always a good idea to tether the hatch covers to the inside of the boat.  The tether can be as simple as a length of nylon line, or a more elaborate setup using nylon webbing with detachable clips. While on the water, they’ll keep your hatch covers from floating away while you’re pulling out your lunch.  While on the road, they’ll give you extra peace of mind and ensure that the covers will reach your destination along with the rest of the boat.  Although my hatches have never come loose en route, a tether is cheap insurance.

- Ross

(You can see the larger versions of the photos on this page on my Guillemot page)