This is meant to be about edges, so there's no need to duplicate the colors. In fact, keep your attempts at duplicating the edges approximate, too. We're aiming to see what the paint want to do when you adjust the wetness of the paper and the brush. Lap gave his paint plenty of room to flow. That blue stroke, for example, was not "designed" to look exactly as it does. The artist made his statement and let it be, confident that whatever the paint did would be fine.
After you've filled up some paper with practice edges, make a couple of invented seascapes using hard, soft and mixed edges. On one, be as fussy as you like, making lots of corrections, rubbing out mistakes, whatever. On another, though, leave the paint alone once you apply it. It should be very informative to see the difference in the overall feel of the two approaches.
Here's another of Piet Lap's paintings: