: I've decided on the overall dimentions of the SOF. 18'3" length,
: 20" beam, 3" gunwales. I don't mind low initial stability but I
: want good secondary. I want a fast seaworthy craft that is easy to roll.
: Low rear deck but not too low (maybe two inches off the water). I'm
: 6'1" and 185lbs.

That sounds reasonable for a general purpose boat, but much will depend on other design factors.

What are you using for your gunwales? Three inches is awfully tall unless you're using something relatively weak like cedar.

As for stability, I've found that the biggest determining factor is getting your butt as low in the boat as possible. Due to the frame structure, it's somewhat natural to set up padding so you sit at rib height. This can seriously compromise stability. For best results, you want to sit as low as possible, straddling the keel stringer. I've found it helpful to remove the center from one rib in the cockpit. Alternatively, you could alter the spacing to achieve enough room. Even rib spacing is not mandatory.

I've made my boats with a DTS of 6.5" at the backrest, which means a layback height of ~7" with the coaming in place (1" tall), since it rests on the slightly recessed backrest beam and I'm sitting on thin pads. I may be modifying one of my boats into more of a "rolling machine" and one of the changes I'll makes is to reduce the DTS a bit and recess the coaming more.

: Cunningham says to set the gunwale angle to 73 degrees (17deg from vertical).
: I paddled a SOF I like with gunwales set at 22 degrees from vertical. I've
: read accounts from builders setting them at 25. Now to the questions: How
: does the gunwale angle affect performance and stability? This is my first
: SOF... In terms of gunwale angle, should I follow the instructions or do
: my own thing.

Higher angles create more sheer. This can translate into more rocker if you follow the curve. It eliminates the need to add wedges to the ends of the gunwales (to achieve the same amount of sheer), saving some weight.

The increased angle means narrower ribs. After looking at a lot of boats I've come to the conclusion that higher angles work best in lower volume boats, as it's more difficult to get much depth with a higher angle, unless you want the hull to be really narrow at the chines.

As for stability, I'm still working on that one. None of my boats have a great deal of secondary stability and the primary ranges from "comfortable" to "yikes!" A squarer hull (wider chines) increases primary stability and more flare increases secondary, but it's a trade-off. In a boat with relatively low stability to begin with, the differences are rather subtle. It's not a case of a minor change making a boat go from scary to rock solid, at least not in my limited experience. It strikes me that a good plan is to assume that your SOF will probably be considerably less stable than any other boat you own and you probably won't be disappointed.