Focus
Hi Paul
Such an intriguing subject like this (composite vs sof) brings out the best in paddlers and builders alike. Thanks for starting this thread!
I see that Sing, Greyak (Kris), Bob D and others have already chirped in with excellent advice so I don’t have alot more to offer…but heck, why not? LOL
My biggest reason for not having a SOF right now (besides cash) is comfort, safety, and diversity of use.
*Comfort - without padding out the floor and doing some major stretching, I cannot be comfortable in a SOF. The ribs bother me going into it, sitting in it, and exiting it. They usually also strip off my paddling shoes unless I use rodeo socks. Unless you are also planning on getting or maintaining good hamstring flexibility, sitting with straight legs for hours on end can be akin to being stretched on a torture rack in a dungeon. Many will say to put a camping pad down to alleviate the pain and discomfort, but then I couldn’t put up with those things as they tend to move with you when you get out anyway.
*Safety - Unless you get a sea sock (bag you sit in that attaches to coaming), your SOF could fill up just as easily as any rec kayak if you exit or are pulled out in conditions. I have seen where folks like Mike Silvius and others have put 1 inch foam bulkheads fore and aft to help make it a bit safer, but would not fully put my life on the line with these as they still leak due to kayak skin flex. Also, if you do use these, you then need to put in hatches as well to access these areas and should also get the bow/stern float bags anyway.
*Diversity of use - We all know that any boat is a compromise of many of our needs and wishes. No one boat can do it all unless your needs are few. That being said, an SOF is very difficult to use as a weekend camper boat due to low volume and difficult in packing/unpacking gear from it. Some can do it to a point (see Brian Shultz) but it is nowhere as easy as a composite with three hatches to store items in. I consider a SOF to be perfect for day cruises (less than 2 hrs) fitness paddling, and rolling for me. Maybe Greyak, Brian S, or others feel differently, but then - hey - this is a forum for opinions, right? 
In regards to the BP that I had built - it was designed to be a day tripper, roller, play boat, etc and I think it will work fine for this. As for any longer trips, overnighters, etc I will go with a larger volume boat such as my Greenlander OC boat or Outer Island.
Also, did anyone point you to the Betsie Bay Kayaks yet? Great boats that use a proprietary layup of wood/fiberglass and have sizes to fit just about anyone and work for daytripping, weekenders, rolling, fitness paddling, etc.
Enjoy your search - Bob D and Kris can tell you that I never stop looking for arrows to fill my quiver. (now if I can only get Kris to let go of that WS Sparrow Hawk)
No bulkheads
According to Derek Hutchinson, the greaest advancement in kayaks is the bulkhead.
My SOF is 17'6", fast, handles nicely, rolls well and isn't a comedy getting into. I love the frames and rugged historical look of SOFs but I am still in the land of reality.
I get nervous in it in cold water when I can feel it flex under me in rough seas plus no bulkheads or hatches never lets me forget that it's a historic recreation. The other thing that has not been mentioned yet is the fact that you loose about 3.5" or more of interior space due to ribs and frame. So many SOFs that people wiggle into would be easy without a frame.
There's a little magic when you paddle a SOF and think about what's going on under you and the feeling and sound of the skin against the water. Even the smell of linseed oil is nice. For me, it has a notible and beautiful place in the kayaking world and the fact that so many people get really hooked on it is good. Plus every one is unique.
Have 3 commercial Skin on Frames
Also known as folding kayaks. I use the Feathercraft Khatsalano most often. Has a really nice feel to it. Very flexy with the waves. Easy to get comfortable in once all the seat adjustments are made and the hips are padded out. Takes a bit more effort to get up to speed than a composite boat, but I took mine on lots of trips.
You could try a Japanese made Fujita in Everett http://www.fujitana.com/ Or head up to Vancouver and demo Feathercrafts either at the factory or Ecomarine, both on Granville Island. .\ Feathercraft will be at Puget Sound Kayak Symposium May 19-20 also http://www.metroparkstacoma.org/page.php?id=97
Not the same as a custom built boat, but it will give you an idea as to the feel.
Yost?
http://yostwerks.com/
Another approach to SOFs…
And if you really want to mix technologies, remeber that George Dyson used aluminum frames with lashed joints on his baidarkas.
Comfort/Safety/Diversity
Some points to add…
“*Comfort - without padding out the floor and doing some major stretching, I cannot be comfortable in a SOF.”
How many have you been in? Whose? The rollaholics? They’re not all build to suit contortionists and sadists!
Of the half dozen or so I’ve been around - I could only BARELY fit one other than my own, and it got uncomfortable pretty quickly just playing around. No way would I paddle it anywhere. I’ve done up to 15 mile non-stop in mine (gets much better after first hour), and if I weren’t 40 lbs overweight it would be as comfortable as anything else (note, I do sit on floorboards - no keel stringer wedgie and no need for foam - but I use a pad for other reasons - see below).
“The ribs bother me going into it, sitting in it, and exiting it. They usually also strip off my paddling shoes unless I use rodeo socks.”
I use a thin (1/4") foam sheet, and this completely alleviates any rib issues (also keeps dirt and skin wear to a minimum. Not needing insulation here I could use heavy plastic sheet or canvas. Others need some warmth/padding. IMO this pad/mat is PART of a SOF. It can move as you noted, but really has nowhere to go (and I tuck one end in between coaming and deckbeam).
“Unless you are also planning on getting or maintaining good hamstring flexibility, sitting with straight legs for hours on end can be akin to being stretched on a torture rack in a dungeon.”
Flexibility certainly helps - but this is TOTALLY dependent on what you build (and again, not on type/materials). Must be custom fit to you - and the only way to really do that is build it yourself or modify. Pretty hard to make one looser
My legs still have a slight bend and are not pressed between top and bottom. As I paddle one thigh is fully engaged with masik, the other is not. My legs are flatter and closer together in my SOF than in my QCC, but not by a huge margin - and I find myself in the SOF position more and more in my QCC. I actually chopped the SOF decks as I originally built in a bit too much room when trying to maintain some comfort. Ended up in a sort of in-between position that was not right. The lower masik offers better support/comfort now. My floorboards were shortened also (just under butt now - were under legs too). They lift me about 1" off the skin - and this means my heels are lower than my but which helps with comfort and paddling mechanics.
Little things go a long way.
“*Safety - Unless you get a sea sock (bag you sit in that attaches to coaming), your SOF could fill up just as easily as any rec kayak if you exit or are pulled out in conditions.”
I don’t use a sock. Too hot here, to much to deal with. I do use float bags. These custom bags fill nearly all the space from bow to footbrace, and back to stern. The kayak is narrow and close fitting so I fill most of the rest. Float bags = bulkheads for flotation.
If my SOF’s completely flooded - there’s really not much room for water. Some around the frame, some between my legs, some at the ends (which also tend to trap air. I have flooded it to as much as it could take - then added more until water inside was higher than outside - and I’m still in trim and still have freeboard! Kayak is heavier, but still paddles quite well as the weigh is evenly distributed. A little slower to accelerate/decelerate - but the stability is remarkably unchanged. Discovering this was a pleasant surprise - and I’m much less concerned about wet exits or holes than I was before (moving from paranoid to reasonably concerned/aware).
The SOF behaves very differently flooded than my QCC, which gets progressively harder to handle and keep upright with a flooded cockpit. All the water is amidships - and sloshes with each wave causing a lot of instability. In contrast, the water in the SOF is distributed evenly and there is no large volume sloshing in a big cockpit area. The added water weight in the flooded SOF could be a liability in surf zone - but other than landing issues I’m not sunk or stranded if I hole it (at least as long as the float bags hold) - while I would be if I holed the composite.
Of course this is just one experience with one SOF - but does show there can be more safety potential than might otherwise be assumed.
Hatches are not an issue for me - as I only day paddle. The hatches on my QCC are always empty. If I wanted to camp out of the SOF I’d figure a way to split the load fore/aft and some in a pack on rear deck. That gets back to your diversity comments - and I didn’t build this one to go camping (if I want to camp - the QCC should be able to haul enough for a month!).
I guess if I have a single point here it’s simply this: If using a SOF - use it as a SOF - with SOF accessories/techniques.
SOF are a system. Trying to use one exactly the same way you’d use a composite kayak, with same gear, is like using a GP the same as a euro. It may work OK, but not optimally, and you can bias yourself against it by doing so.
All that said, I do only day paddle mine, on mostly calm and always warm waters (but that has more to do with locale than kayak type).
Dimensions…
your SOF would be the same size as my Ronin, if you add on 1.5" to the foredeck and had a standard 16x20" cockpit. The Ronin was my all around day boat, could paddle for hours in that with the occaisonal "nature break". I used to take that out to the harbor islands, year round, and felt quite comfortable with it. I loved it for just paddling but it was not the greatest for surfing. Not enough volume and rocker so it would tend to pearl and broach pretty quick. The 2nd SOF, Kaze, addressed some of that by being 18.5"x17'2" with a back deck of 6" and foredeck of about 8" and, more important, about 3.5" rocker in the front and 2.5-3" of rocker on the back. The middle section of Kaze has minimal deadrise (almost flat for quicker planing) compared to the the Ronin Means Kaze is much more optimized for surfing than the Ronin but will probably be a bit slower in point A-B paddling.
The fact of the matter is that, if you know somewhat what the different characteristics of a hull design will do, you can set out to make a SOF to perform closer to what you want in the conditions that you prefer. That's one of the main difference (attraction) of a sof compared to a mass produced kayak. The sof is literally custom to my size and preferences. A mass produced boat is optimized for that generic person within a certain size range.
sing
here is the perfect video for you to see
http://www.youtube.com/watch?v=gYyvIExWkqU&mode=user&search=
from Shaman kayaks
kinda funny