Mate,
Each to his own re the most suitable craft for a trip like this but thank you for your confidence in me.
I am not exactly familiar with that area of our coastline but have surfed it in places many years ago. If memory serves me correcty, there are plenty of headlands that provide relatively shelterd places to get in and out through the surf.
I would be counting on at at least some times when you will have to come in and go out through the heavy surf that breaks on the open beaches there. Regardless of which boat you take, you will need to develop serious surf knowledge and skills in a kayak to do this safely.
I don't think a longer boat is necessarilly, a better boat in surf conditions. A shorter boat will be less likely to pearl or broach when coming in through surf and provide better maneuverability. It will also provide better accelleration for the power bursts required when punching out between the sets.
These conditions are only a small part of the overall trip however (but I would argue the most critical and fraught with danger.)
A longer boat should provide better overall load capacity, glide and distance capability in a day. Everything in kayaking is a trade off or compromise of some sort.
As a new sea kayaker, I would be inclined towards the shorter, 15'6" version and get to know it very well in surf and ocean. It will do this trip well enough I think anyway and I believe you would probably be less likely go get into trouble in the surf.
As Jack has said, you will also need to aquire skills in self rescue and become competent in them
I am no boat designer but have some pretty definate ideas on what I think will work.
I think this boat will be a winner for several reasons.
1. It is a thing of beauty to behold. it just looks "right" to me.
2. The generous beam, combined with the soft chined multi panelled hull should provide very good initial and secondary stability. This will make for a very forgiving boat for intermediate paddlers
3. It should track very well with minimal wind signature or weather-cocking. This would mean that a rudder is not necessary but if fitted would mean minimal usage. Deploying a ruddr really does slow you down.
4. I think I have said it before, but I would call this boat, as drawn at the moment as being a recreational Sea kayak. What I mean by this is that its primary function would be day paddles off shore or one or two days. but still very capable of doing a multi day trip if desired. This is exactly what the Contour is and is, I believe, why it is so popular here. It is just soooo versatile.
I am dead keen to build this boat - in either the 14'6" or 15'6" version. Either one will do all
I want from such a boat. And, I think will leave many of the big name, longer, so called sea kayaks in her wake.
Regardless of what kayak you finally settle on, you will probably want to re-supply at some point during the trip. There are plenty of little towns along the way where you can do this. This is what I would want to do.
Jack probably makes a good point re the dip in the foredeck but from my point of view, it would probably be harder to to build into a deck than would be justified by any benefiet gained from it. That is why we have spray skirts. I am very happy with the hull and decks combination as drawn. (but again, that is just me)