Hi Mark,
I have built both the Razor Billed Auk and the Nordic Arrow. I built the RBA for racing and it worked well for me for several years. It is a fast boat at 19' x 20" I could hold 6.0-6.2 MPH over ten miles on a good day when I was in my best shape. It is competitive with the Epic 18, Westside EFT, QCC 700, Etc. I also competed against TK1's (development boats) such as Nelo Razor, Kirton Talisman, Simon River Laser, and, Plastex Marathon Master, the latter two I have owned.
In my opinion, the Razor Billed Auk is the sweet spot between a fast flat water boat like the tippy TK1's and the Mystery and Nordic Arrow strippers. It is close in feel to the epic 18. The races I paddled were a mix of flat water rivers, rivers with current, bouy turns, and open water inland lakes. Anything from class 1 WW to 1-2 footers, and some overland carries (with 36#). The RBA is very seaworthy (to a point). I have never been knocked down while paddling it, can't say the same for my other boats. It is a great fitness boat, racer, club paddler, overnighter, etc. I find it my go to boat most of the time, mainly because I can keep up with younger, stronger paddlers, in slower boats. It's a sports car of kayaks, fast and fun even though I no longer race.
I have always paddled it without a rudder. However, I suffered at bouy turns. I will probably add one this winter, just to make life a little easier.
It's an easier build than most designs because it doesn't have any hollow sections. I highly recommend it for your needs. You will not out grow it or be afraid to paddle it when it's a little rough. A round bottom boat as narrow as you suggest will only be good for all out speed on flat water. Boats like this are for skilled hands, in the right conditions. You probably won't paddle it much. I suggest you move into this arena in steps, starting with something faster than what you already have, but still seaworthy, so you will gain experience by paddling more, before jumping into a highly specialized craft.

The recently finished (almost) 20' X 20" Nordic Arrow is a completely different animal. it is a sleek, round bottom, rocket!! However, I have a difficult time paddling in rough water. It's stroke- brace- stroke- brace, although It's much better behaved on flat water. I will need much more time to get used to this one. Stay tuned.......

If you need more info on either design, let me know.

Larry C.

: Can anyone steer me towards some fast boat designs? I have a Night
: Heron, which I'm quite happy with. But when I'm trying to push
: my speed a bit I see the wake off the bow and think I could be
: going faster. The Night Heron is 18' with a 20" beam and
: relatively hard chines. I'm thinking 19 or 20', maybe 17 or
: 18" beam and round bottom. Am I on the right track here for
: speed and does anyone know of any stripper designs that fit
: these parameters?

: thanks,
: Mark