Ekapi,
I've tried the Target Coatings EM 9300, PPG's Break-Through, General Finishes 450, plus a couple other water based finishes. I had the best results with the General Finishes 450. After a couple hours in the water the finish softens and can be scraped off with a finger nail. The kayak with the Break-Through has grass embedded in the finish after placing it on some grass after two hours in the water. I had wanted to use a water based product to spray. I'm going be using Zar oil based poly on the next boat. I did a water soak test and after 5 days in the water the Zar did not soften. I'll apply the Zar with a foam brush. It's not recommened to spray the Zar because of bubbles, though I wouldn't spray it if it was. I did a test on some scrap material with a foam brush and was able to get a fairly smooth finish. I can always use some wet / dry 600 grit followed by a polishing compound.
Bob