Consider a tube connected to a hole in the hull and running up to the deck, it will act like a sight tube on a tank (what you could put on your motorcycle tank to gage the gas inside) and allow you to see the depth of the water outside the hull ... it will rise and fall with the waves, right?
Now pur a flapper valve at the bottom so water can only enter the tube from the bottom ... how high will the water get inside the tube? As high as the highest wave, as anything less will not be able to overcome the column of water already in the tube that wants to be at equilibrium with the outside level.
And what you are trying to pump out is denser than water, so if I fill the tube with that it will not reach the tops of the waves.
Your best bet is either windmill (not mentioned) or draft animal power (abundantly plentiful I believe) and the way water has historically been pumped in the middle east (where I understand there is sometimes a shortage).
Why go hi-tech when you can go 'K.I.S.S.' and an easily repairable\replacable system, especially if it was "known" technology:
In 1750 BC, in Babylon, Hammurabi promoted the extensive use of water-lifting devices such as counterweights
and animal powered wheels.
for pictures of them see
http://www.ummah.net/history/scholars/water/
Enjoy.
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