Kayaking and vortices

Last summer, when I was kayaking hungrily over the Wadden Sea and a seal was following me, I looked at my paddle and saw that it did more than I want.

Every time I put the paddle blade in the water next to me it was making one vortex on each side of the blade! Well, actually not the paddle did it, but me! The fact was that I myself was losing energy to make those two vortices each time I put a paddle blade into the water.

On the picture (it's not me by the way) you see the two vortices: one at the shaft and one in the middle of the blade. So after one left stroke and one right stroke four vortices are made.

Estimating that the energy in one vortex is about 10 Joule (yes, I made some doubtful calculations), the total energy lost by doing one left and one right stroke is about 40 Joule. I do both strokes, left and right, in about one second so I lose 40 Joules per second, which is the same as 40 Watt.

Considering that I am not very trained and can produce about 250 Watt on the Wadden Sea, those vortices have cost me 16% of my power!

That's quite much.

So, how to get rid of those vortices? Vortices arise along sharp edges moving through water, like the sides of a paddle blade. Rounding the edges may help a little. But better is to get rid of the water flow around the blade, then no vortex has reason to occur.

If we had a blade through which the water could flow as there were no blade at all, so with no resistance, we would have no vortices. But without a blade there is no resistance to move forward with our kayak.
We need a special blade. A blade that is non permeable (100% closed) in the middle and 100% open at the edge where water can flow without any resistance. In between the openness should vary from non permeable in the middle to fully permeable at the edge of the blade.

A blade like this will not show flowing water around the edges and no vortices will arise. Making a blade like this in a simple way means drilling a lot of holes through a blade - that is to say in the middle none and going to the edge more and more.
Better would be to use a suitable material, some membrane ranging in permeability. And to compensate for the openness the blade must be some bigger of course.

But when all the work is done I should sign in for the kayak championships!