Thursday, June 03, 2010

Fitting an electric pump to a sea kayak

An electric pump will allow you to start paddling and bracing immediately after performing a reentry and roll in rough conditions. I believe it makes a significant contribution to your overall safety in challenging conditions, should the worst happen and you find yourself out of your kayak.
There are many different web pages on how to do install a pump but many are complicated, involving many connections switches, relays and connections and some are compromised by the owners reluctance to drill a hole in the kayak. In a marine environment, the more connections you have, the more likely it is that one will fail.

I have chosen a different approach, which uses a minimum number of connections. The Rule 25S-6WC 500GPH automatic bilge pump is designed for jet skis. Inside the pump body an electronic circuit spins up the pump for about a second every 20 seconds. If no resistance (water) is met then it switches off. If resistance is met, it will carry on pumping until air enters the pump inlet when it will stop. After this it will go back to spinning up every 20 seconds. (Some other Rule automatic pumps spin up much less frequently and are therefore unsuitable for kayaks.) The battery draw is negligible. I used it for 10 days in the Outer Hebrides and at the end of the 10 days there was enough battery power to empty the kayak several times. I have chosen not to use a switch or a fuse. I chose to use a sealed lead acid battery because the pump is 12 volts and if you were to use rechargeable AA batteries you would need 10, which is a lot of connections! Also most NIMH AA rechargeable batteries don't hold their charge in storage and it is a hassle to charge 10 just before you go out. They also have poor cold weather performance compared with a sealed lead acid battery.

Rule 25S-6WC pump
12v 1.3Ah sealed lead acid battery fitted with...
snap together connector which is soldered to the battery terminals.
(I used to use simple spade connectors straight onto the battery terminals but I found they came off.)
12V SLA trickle charger, don't try to use a car battery charger on a small battery like this!
Some 3mm sticky backed foam to stick on the back of the battery and the bulkhead, where it will fit against.
Velcro hook and loop tape to stick onto the foam pads on the battery and the bulkhead. (I found you get a better "stick" using the foam between the Velcro and hard surfaces.)
A 3/4" skin connector for the hose.
About 10" of 3/4" hose
Unibond "No more nails", waterproof adhesive, which is much more effective than silicone sealant.

The fun starts drilling the hole with a hole saw. I like to put pumps in front of the footrests, next to the forward bulkhead. Put some tape over the gel coat and drill very slowly.

Bed the connector in a little adhesive and screw it up from inside. Glue the pump mounting base (blue) to the hull, because of the vee bottom, I have stuck it slightly off the mid line to get it square on the hull. It is best to roughen the pump base and the hull with coarse abrasive paper then clean both surfaces with a solvent such as alcohol. Leave the pump base glue to dry for 24 hours then fit the hose, heating it in hot water will make it more flexible. Clip the pump into its base. Now drill two 3.2mm diameter holes in the middle of the bulkhead and push the wires through to the front compartment. Seal on both sides with glue. Leave enough wire to bring the pump back to the cockpit opening for cleaning its filter (if it ever gets blocked) and use cable ties to secure the loose wire to the hose.

Working in the front hatch, solder the connectors to the wires. Working outside I find it easier to use one of the little high temperature jet butane lighters than a soldering iron.

Push the plastic connector on to the two terminals and give it a good spray with water dispersant.

Now the whole lot can be assembled together and the battery stuck to a Velcro pad on the bulkhead. You will now hear the pump spin up then stop every 20 seconds until you pull the connector apart. The connector can only clip on one way so you will not be able to reverse the polarity by mistake.

I have tried three different one way valves in the hose. Even the best reduced the flow rate by 50% so I don't bother. You can fit a kitchen sink plug to the outside of the connector. Some people suggest putting a loop in the hose to prevent sea water coming in through the pump but the Rule instructions specifically warn against that as it can create an airlock which will stop the pump.

Does it work?

You bet it does and its simplicity makes it reliable!!

This is why I do not like switches. This switch was mounted in the day hatch with a waterproof boot covering the toggle which went forward through the rear cockpit bulkead. It has seen three seasons' use and was sprayed twice per year with a Suzuki brand wax spray for protecting outboard motor electrics. It did still work when it was removed but for how much longer...?

There are some other links to installing pumps,
Here and


  1. Excellent article, thanks. I take it there's no need to waterproof the battery? I wondered if it got a bit fizzy if immersed in seawater, but hopefully that shouldn't really happen.

  2. Hi Tom the front compartment is pretty dry but I did test it by flooding it with sea water. The battery and pump carried on pumping.


  3. How loud is the pump with it kicks on every 20 seconds and is there anyway to vary the pump interval?

  4. Hello Bryan, you can hear it if it is very calm but otherwise you will not notice it. There is no way to alter the time. There is another Rule automatic pump that spins up every 3 minutes but that is too long to wait.

    I think the noise of the pump is also very attractive to dolphins!


  5. If possible I put my electric bilge pumps behind the seat because it's usually the lowest part of the hull so it picks up a bit more water.
    My installs have the battery in day hatch and use a magnetic switch instead of the automatic switch that comes on every 20 sec.
    I do like your simplicity (no switches and no relays) and possibly higher reliability, however the auto Rule pump costs way more than the manual one.
    If I calculate the waterproof box and related switch components in the price maybe the cost is similar :-)
    More details on a bilge pump switches at:

  6. G'day Douglas,

    as a Scot living and paddling down under, I get a hell of a kick out of your site, your adventures and of course your wonderful photos. Many thanks.

    I like the little pump, I'd looked at the automatic Rule pumps before but not seen that model. Thanks for posting it. The lead acid battery is a good choice. I use a 2AHr Yuasa one, NP2-12. It's very slimline and fits well in an otter box. The AAs are simply not designed to deliver the sort of currents required, I wouldn't recommend them.

    kind regards and keep up the wonderful work please,

    John Anderson
    Budgwewoi, NSW.

  7. G'day Douglas, The subject of electric pumps has caused almost as much controversy down here as the old skeg V rudder debate. I use (on 3 different boats) a simple battery like yours installed in the day hatch, connected to a waterproof toggle switch deck mounted just above, then to the Rule pump behind the seat. The switch is protected by a simple plastic conduit saddle No problems after 3 years. Gnarlydog has also fitted a pump behind the seat of his Nordkapp LV, with a bit of his well documented ingenuity

  8. Greetings Gnarly, I do not think it matters whether the pump is mounted at the front or rear of the cockpit. Yes the cockpit rear is a cm or two lower at rest, on flat water but not when the kayak is pitching in the waves that are likely to have put me in!

    There is more space at the cockpit front (unless you have a custom bulkhead). Many recent British kayaks have sloping rear cockpit bulkheads that leave insufficient room on the deck behind the cockpit coaming to fit a pump outlet. Rockpool get round this on their factory fitted electric pumps by putting the outlet through the side of the hull. This means they have to use a one way valve. I found that the same valve that Rockpool uses caused the pump flow to be reduced by more than half.

    I note you have used a loop in the outlet hose as a valve but in their UK data sheets Rule specifically advise against this (in underlined, bold CAPITALS!!) duie to the risk of airlocks stopping the pump.

    Hello John and thank you, I also have that larger capacity battery which I use if I am on a longer expedition but I find the smaller one has plenty capacity for up to a week away.

    Hello Owen, good to hear from you. I have edited the original post to show a photo of a three year old switch which was in the day hatch of one of my kayaks. A difference between Australia and Scotland might be dampness. It's wet pretty much all year in Scotland, which really goes for boat electrics and Scotsmen. Hence my brother lives in Melbourne and my brother in law in Brisbane!

  9. Douglas, you are correct on the loop in the hose potentially creating an airlock. Occasionally in some set ups the pump just grabs air and not water.
    A quick stop/restart of the pump (possible with a manual switch) fixes the problem.
    I am not sure what kind of non return valve Rockpool uses but with all the valves I have used the same problem of airlock occasionally occurred.
    I believe Rule is against check valves too.
    Unfortunately having the outlet somewhere behind the cockpit puts it low enough that water will enter the cockpit by the outlet hose in rough seas. Not a lot but over an hour or so there is enough to slosh around and needs to be emptied. On a recent Rule install with a Whale (brand) non return valve the airlock problem became frequent.
    The loop in the hose has been so far the least problematic for me.
    Needless to say that your outlet location is high enough to prevent most water reentry. I notice that the outlet is off centre. I have seen one install where the water will spray the paddler’s face in head winds :-)
    And I am with you on the toggle switch corroding: mine did too after a year.

  10. Hi Douglas, I have been looking at retrofitting one of my boats with with an electric pump for at least five years. I have reviewed many different sets of installation instructions on-line, but I have always been put off by the complexity. As I have communicated to Gnarlydog I am not the brightest guy when it comes to home improvement projects. You have provided the first set of instructions that I have seen which may actually entice me to give it a try (e.g. simplicity).

    BTW, I am counting the days until you publish your review of the Cetus LV.
    Thanks again, Joe

  11. Gnarly, my exit is high enough not to let water in unless it is very rough but I do have a bung for it!

    Thank you Joe, full Cetus LV review soon!!!


  12. Great install on pump, very simple, I am not sure if I am understanding the functions of the automatic pump, I thought as long as the pump detects water it will engage, whether it is 20 seconds or 3 minutes cycle, the comment on the longer cycle in a kayak dose not make sens to me, One year new to sea kayaking and loving it, Great site with great info

    1. Hi John, thank you. The problem with automatic pumps is when you are in rough water, the water in the cockpit is slopping about. At one point the pump will suck air and stop. A pump with a 20 second cycle will start pumping again in 20 seconds but one with a three minute cycle will take three minutes that is a long time to wait after you need a quick bail out. Then if it sucks air soon after staring again, it's anther three minute wait!
      Douglas :o)