RE: [Paddlewise] Electric Pumps ??

Electric pumps in a kayak are always a compromise between pump output and 
power consumption.  I think the Rule 500 and similar models from other 
manufaturers are a good option, since they run on small bateries for quite a 
while.
Larger ones, like the 1100 gal/h draw exponential more power from the 
batteries.  My cockpit with me in it (water displacement) and as full with 
water as you can get in is pumped out in ~4 minutes with a 500 gal/h pump.  
And after reentering there is in most times less water in the boat than 
after filling it up with water to the underside of the coaming.
I use Rule 500 pumps powered by Alcaline AA cells in line in my boats. The 
little AA hold up for ~40 min - 60 min of pumping.  A single set lasts me 
for the seasons rescue practices, a second fresh set goes in for "real" 
trips.  However, I carry a manual pump as backup.

Batteries and switch are in a 500ml Nalgene wide mouth bottle.  The switch 
is mounted trough the lid, the outside covered with a rubber membrane (i.e. 
piece of a rubber glove) glued down to the lid with aquaseal.  Aquaseal also 
selas the little holes in the bottle were the 2 cables go through.  However, 
after each trip I take my bottle out and open the lid to dry it out.  
Otherwise it doesn't take long and the bit of moisture collected by 
condensation corrodes the cheap contacts of my battery holder away.

I tried to come up with a electronic switch, triggered by water closing the 
contact between 2 electrodes. It works, but I haven't built it in yet.  (the 
circuit is a darlington 2 transistor circuit switching a relay for the pump 
power circuit). Reason for trying this system is that I find it no problem 
to start the pump before reentering the boat, but once the water is out the 
pump keeps running and you have to open the skirt and fiddle around to 
switch it off.

Ulli

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