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22. Hatches 4 - seal gasket and hardware

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Putting in a rubber foam gasket is the very last thing to be done to the kayak after varnishing and hardware installation.

Closed cell rubber seal or neoprene gasket are essential for long service life. The one used here is 3/8" wide and 5/16" thick.
The self adhesive seal gasket fits snugly into the channel groove. Its uncompressed thickness is almost flush to the surface of the deck.

Because of the profile of the channel, the lid compresses the seal only about 70% (in thickness). The partially squeezed gasket can thus maintain its 'shape memory retention' with quick spring back. The molded 'bead' in the seal-channel will allow the lid only so deep as to be even with the deck. This makes it possible to remove it without the help of any handles or hardware.
Securing the lid makes sense for obvious reasons but a short tie also prevents the wet lid from dipping in sand and contaminating the seal unnecessarily.
I often use stainless lashing hooks and 1/4" bungee cord to hold the lid in place. (Defender marine store has them).
Some builders also use wooden eyes/hooks as well as nylon webbing with buckles to secure the hatches.

My choice of stainless hooks is for practical reasons. They are of the lowest profile (read: little deck spray) and easily removable for maintenance such as varnishing. Sealing the wood in the drill holes is vital. Matches work well.

If you don't care for heavy "stainless" or bulky "wood", check out the super light hardware you can make yourself from carbon fabric.

Finished flush bow hatch with water tight seal.

I did not add any grip handles to the lid for aesthetic reasons. You may find that this hatch seal design is very air tight and the lid removal can be difficult without a handle or some 'vaccum relief' orifice or valve.

What happens is that when you close the hatch on land, a volume of warm humid air is trapped inside. When you put the kayak on the water, the compartment air cools down, and the pressure is reduced which causes to lid to get sucked down.
I personally like the security of vacuum assisted hatch seal but if you don't, the compartment has to be vented (purged) with a small 2mm "breather port" made in the bulkhead. Make it in the center (laterally) about 2/3 up (vertically) from the kayak bottom.
[Don't break your fingernails needlessly ;-) ]

Note of Interest:
According to the Ideal Gas Law, the kayak compartment starts with pressure P1, volume V1 and temperature T1. When the air cools down, T2 becomes lower, the volume of the compartment V2
remains the same so P2 must go down for the equation to hold. Now, P2 is lower relative to the atmospheric pressure (P1) so now you got small vacuum in your kayak which holds the lids without any 'strap down' assistance.
      (P1 x V1)/T1 = (P2 x V2)/T2 = constant
P = pressure
V = volume
T = temperature


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