The old North Bay is 20" wide, versus 22" in the Shearwater, so it'll be faster than the Shearwater, all things being equal.

I had a North Bay forever and really liked it, especially for surfing.  I have seen various theories advanced as to why we don't make it anymore.  The real reason we discontinued it is that, at the time (2001), retiring that design was part of the agreement that included rights to the kit for the boat's nearest competitor:  the Arctic Hawk. Also, at a time when it was more costly to have a lot of kits in inventory, we just didn't want so many competing kayaks under one roof.

The North Bay did so well that from time to time I think of resuscitating it.  The only change I'd make is to reduce the rocker in the stern.   

Reduce the rocker in the stern?  Really? 

John's the expert, but I'd say the biggest difference between the two will be handling, from what I've read about the shearwater.  The Northbay is a wonderful boat and I really preferred it to the Arctic Hawk and the Chessies (no Shearwater offered when I bought mine) but it does have some heavy weathercocking issues.  A skeg fixes the worst of them, and it's mostly correctable with paddling anyway, but can be tiring after a while.  It will be faster than the shearwater but not really as fast as its length might suggest because it loses about 8 inches to a foot in waterline because of the angled bow and stern.  Granted, I sit pretty high in mine because it's almost always empty and I'm fairly light (165-170 pounds).  That said, I keep up with anyone I want to that isn't a racer trying to race me and I very rarely paddle at 100% effort.  

The NorthBay holds a lot more gear than I expected and is far more stable than it initially feels when you first start paddling it.  I've heard the Shearwater is similar in that regard though. I think the Shearwater will be a better roller, but the NB isn't particularly difficult to roll (though I haven't mastered it yet).  If that's a big factor for you, a couple of minor changes during build will fix it to be a fantastic rolling boat, in my opinion.  

If you're much larger than me (as I said 165-170 pounds and 6'1 with size 12 shoes) the NB may be a little tight for you.  When I sit "comfortably" in my boat my knees touch both side walls though I sit a little "bow-legged" and others may not have that issue so much.  I don't feel like the boat is too tight though, so I think a Shearwater will feel positively roomy by comparison.

If you have any opportunity to test any out, even on dry ground, just for fit, I'd suggest taking that opportunity.  Just my thought on the whole thing...

Hopefully my comments are helpful.

FrankP

best comments I've heard and very helpful. I'm 180 lb. Would I be likely to get more speed and the desired less rocker if I stretched the design a foot or so?

>>>>>>>I'm 180 lb. Would I be likely to get more speed and the desired less rocker if I stretched the design a foot or so?>>>>>>>

Then you'd have a Night Heron Stitch & Glue.  Also a fairly "loose" boat like the North Bay, but fast and fun.  I think you might find the North Bay tight on you.

No, you don't HAVE to do the parti-coloured staining scheme....

Are you saying it could be  faster or slower or the same? I'm not too worried about tight fit as I've had a Pax 20. What do you mean by a loose boat?

Revensdale, with your extra weight you'll have a little more waterline than I do in a NorthBay.  You should still be fairly comfortable in the boat unless you're particularly short and round, in which case it might feel tight.  The extra weight will help a bit with speed, but honestly I don't see you gaining a whole lot more speed from it, perhaps a sustainable naut per hour (which adds up) but I wouldn't expect anything more than that and wouldn't really expect that much speed gain. 

As for adding length, you could do that, but I'm not experienced enough to know exactly how much affect that would have on performance if you just "stretched" one dimension of the boat without similarly stretching the other dimensions. 

"Loose" means it will weathercock a bit and "fishtail" in following waves or in wind.  For some people it's a desireable trait for a boat, especially when you can eliminate it by dropping a skeg (as you can with the NB).