Different types of Kayak Hatches
Wet or Dry – Leaking or Normal - Things we think you should know
Kayak Hatches – Leakage Rates:
The hatches on these are very good but this is not the standard used for kayaks.
Put simply the more complex a hatch the more it will leak at some time.
Rubber Hatch Covers.
The rubber hatches used on advanced expedition sea kayaks and some other kayaks like the Feelfree Nomad and Perception Triumph 13 are the driest because they are fitted over an upstand. Time will eventually take its toll as the rubberised cover will stretch a bit and eventually perish – this is part for the course. Your tyres don’t last forever nor will your hatch cover.
Screw Hatch Covers
These are quite reliable bits of kit. Any leakage is more likely to be around the hatch seating than the twist hatch seal itself. Nearly all kayak manufacturers use a sealant that in our opinion is too thin when applied. Twisting, heating and cooling of the kayak can allow these hatches to leak a tiny bit. If we find a hatch that is drinking too much we fix it with Arbor seal. This is 5mm diameter sticky gunk that stays where you put it no matter what. Some of us used Arbor Seal whlist working on ships and submarines in another life. This is a useful link http://www.arbo.co.uk/arbo-sealants/.
Time will take its toll on rigid screw hatches as their relationship with sand is not good. Also these rigid plastics ever so slowly absorb water and swell. I love my Hobie Outback to bits but the round hatch will need renewing long before the kayak will - you cant do anything about the laws of physics.
Twist Lock Hatch Covers
These are now all the rage and make selling a kayak much easier and come straight from the add a gizmo shelf. These hatches perform quite well when water falls directly onto the hatch. Minor leakage will occur in rougher conditions and when working hard at self rescue routines. Water ingress will be less than a few litres and will not prejudice the stability of the kayak.
Non Hatch Covers
To be called a hatch cover the fitting must be designed to prevent/reduce water ingress into the kayak. A hatch "cover" is something completely different. Take the bow cover on the Feelfree Moken 10 as an example. It is not a watertight fit nor was it ever intended to be so. It is a fixed cover that you can safely open afloat which does not open up to the inside of the kayak. You can slosh some refreshing water over your catch and the water runs out through the scupper holes. Provision is made for your plotter battery in this space but that should be stowed in a dry bag.
Boyles and Charles law!
No I hear you cry I hated this stuff at school (but this is really useful stuff for a kayaker to know).
(P1 x V1) / T1 = (P2 x V2) / T2 Remember now?
P = Pressure
V = Volume
T = Temperature
1 = Outside of Kayak
2 - Inside of Kayak
Your sit on top kayak is sat on the beach at 30C when you close the drain plug and throw yourself and the kayak into the cooling English Channel at 15C. T2 drops as must P2 and your kayak will suck air and water into itself until P2 = atmospheric pressure. The reverse is also true. You beach your kayak and leave it in the sun with the drain plug sealed. T2 rises as must P2 and if that’s as much as ½ a PSI (sorry I still do Imperial Units) and your kayak surface area is say 3 sq yards 1 x 3 x 36 x 36 = 3888 lbs force (hull and deck). You will be very glad your hatch leaks a little to allow the pressure to dissipate – better still undo the drain plug.