Electric Pump for Sea Kayak, Mark III

For several boats now, I’ve been outfitting my sea kayaks with electric pumps. (My reasons are explained in the first part of this posting.)

an electric pump in a sea kayak

So I’ve fitted my new-to-me Valley Etain with an electric pump as well. The overall design is pretty similar to my last pump, with a waterproof Pelican battery box designed to let me run the system on either 12 rechargeable AA batteries or 8 alkaline AAs. A stretchy Velcro strap and a pair of stainless steel footman’s loops hold the battery pack in place against the bulkhead at the back of the cockpit.

pump battery system, out of its box

the electric pump and battery box in place behind the sea kayak seat

Also as in my last pump, the on/off on this system is a magnetic reed switch, soldered into the positive wire and “potted” with marine sealant inside a short length of PVC pipe so it’s completely watertight.

One change I did make was to place the potted switch on the right side of the cockpit rather than under the front deck as with my other boat. This is partially because I found the activating magnet on the front deck was messing up the hiker’s compass I like to keep in my chart case to orient my maps. (On both the Etain and my Tyee sea kayak, I also have deck compasses, but they’re far enough away from the magnets not to be affected.)

the sliding actuator magnetic on the outside of the kayak

The other reason for locating the switch and sliding magnet on the right side was to create a nice symmetry with the slider that raises and lowers the skeg, which is on the left side of the cockpit.

When it comes to electronics, I haz sad skillz rather than mad skillz, so it took me a while to realize why the first couple of magnetic switches I made froze in the closed/on position and wouldn’t turn off after the magnetic was removed: the original reed switches I’d used on my old system are no longer made. With the best replacements I’d found, the higher peak amperage of a 500GPH pump was enough to arc the contact permanently closed. Once I dialed back to a 360GPH pump, the problem went away.

The magnet that activates the reed switch is sewn inside a little nylon pouch, threaded onto a stretchy Velcro strap that runs between a pair of stainless steel footman’s loops on the right outside of the cockpit. (The strap and footman’s loops are identical to the ones that hold the battery pack in place in the cockpit.) I slid the potted switch into an old Cordura flashlight holster, ran thin bungi cords through either end of the holster and threaded those through cable clamps mounted on the inside of the bolts that hold the footman’s loops. So the sliding activator magnet and reed switch are held exactly parallel on the inside and outside of the hull respectively.

the magnetic reed switch on the inside of the hull

If a chain is only as strong as its weakest link, a pump system is only as fast as its tightest bottle neck, so I used a wider drill bit to core out the mushroom head thru-hull fitting a bit and widen its inside diameter.


Here’s the finished product in action:

Update June 2021

On a trip this spring, I discovered the Pelican Micro Case housing the batteries had flooded, wrecking the batteries and wiring. This is the first time I’ve experienced this after having made at least four such pumps (three for myself and a fourth for a friend.) But it pushed me to do something I’d been considering anyway: running the wires through the rear cockpit bulkhead and into my day compartment. So now the battery box sits in a (nominally) watertight space and has the second-tier protection of the Pelican Case.

At the same time, I spliced a non-return valve into the hose running from the pump to the mushroom head through-hull opening. This will take the place of my previous foam “corks” and will mean I don’t have to remember to reseal the opening after I’ve turned off the pump.


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