There are so many great kayak plans already out there that you have to ask yourself if it is worth the time and trouble to make up your own plans using this method. For $100 plus you get a proven design free of costly mistakes. I have built kayaks from plans by Guillemot Kayaks, Redfish Kayaks and Bjorn Thomasson Design and never regretted it. The plans are fail safe and you always end up with a beautiful kayak

I agree with Bob on this.

About 'copyright:

However, I wouldn't hesitate to copy a commercial kayak again, as a one-off' for my own personal use and amusement. I wouldn't publish plans or sell multiple boats that were copies of commercial boats.

No good boat designer just starts with an 'empty mind and empty sheet of paper' ...every design builds upon and is related somehow to those that went before.

Nowadays I find it more interesting to modify and repair older glass kayaks, and to 'scratch build' boats from plans i purchase. And those 'from plans' boats need to be boats that are different from what's available in the commercial marketplace here in Canada & US.

If you talk to 'folks who were there' as kayak designs evolved and were produced commercially, you will hear plenty of stories about competitor's boats being copied exactly or with very little modification - 'splashing' a mold from a competitor's boat.
One famous company got started that way, and they even used the same logo as the original boat for a while...so the story goes.