I like that idea.
It uses the properties of water and gravity to solve the problem of water flowing down the shaft. So much neater than the rubber rings one usually sees around the shaft.
The paddle I used with my sit on top had two little notches, one on each blade.
not the same as Pierre's notches obviously;
but apparently designed to stop drips too.
I've no idea how much difference the notches made in comparison to other paddles but I always got soaked from drips.
I like the look of those wooden paddles
If you're thinking about buying a boat and getting into Canoeing, seek some professional coaching