Here is another perspective: West Hansen is responding to a similar question from Dan Grubbs just a couple of days after the Kansas River race.
I'm always balancing the issues of weight, speed, stability and versatility. I prioritize the four depending upon the length of the race and the make up of the race course. Unfortuneatly, the ideal answer is to have access to several boats and choose the appropriate one for each individual race. Here's a quick and dirty breakdown of what boats are out there in the marathon and ultramarathon world, however I did not include regional races that have their owns restrictions like the Old Forge race in upstate NY, the perot bayou races in Louisiana or the Yukon challenge that took place last weekend.
ICF (International Canoe Federation). An international organization that sets standards for lots of international races and most importantly, the olympics. Very tippy, very fast, used primarily for sprinting though common in Europe, Australia and South Africa during marathon distances (not ultramarathon). Only kayaks are allowed rudders and double blade paddles.
K-1 - solo kayak, K-2 - tandem kayak, K-4 - four person and really fast, C-1 - high kneel canoe, C-2 tandem high kneel, C-4 you guessed it.
USCA (United States Canoe Association) was formed in the 1970's as a breakaway club from the ACA (American Canoe Association) to concentrate more on competitive marathon canoe racing. Set standards that were aimed at allowing recreational boater to transition to racing without having to go ICF. All boats are sit-down type and use single blade paddles with no rudders: C-1, C-2, Standard Class, Aluminum.
OC (Outrigger Canoe) A whole different set of standard that are geared towards the open ocean racers. This is the Hawaii Five-O stuff. Currently the New Zealanders (Kiwis) are the ones to beat, but Aussie, Hawaii, California and several other Pacific ocean based lands are competitive. OC-1 (solo), OC-2 (tandem) and OC-6. All use single blade paddles. Big boats have minimum weight restrictions. All have outriggers.
A close cousin of the OC crowd is the surfski. That's what I raced last Saturday. It doesn't have any restrictions, but is geared towards being able to handle waves and use double blade paddles. It has a pretty substantial rocker (curved bottom from bow to stern) to be able to catch waves in the open ocean to go faster. Has an understern rudder or overstern rudder, which has been adapted for river running. The surfski comes closer to an ICF boat, due to it's skinny hull, but since there are no restictions for size it is longer to create more bouancy.
Unlimited Class. Now we're getting to the weird stuff. This class was unheard of outside of Texas until very recent years. Typically, to level the playing field, races required classes to fit within the USCA, ICF or OC guidelines. The classes never competed against one another. Either it was a USCA sanctioned race or and ICF or OC sanctioned race and never the twain shall meet. The Texas Water Safari, being the crazy aunt in the attic (we don't have basements), since it's inception 45 years ago let anyone enter with any boat they wanted. Creative minds took over and boats were developed that could handle rapids, ultra-distance and open ocean. As paddling skills and designs improved over the years, the boats got lighter, tippier and more expensive - but still met all the requirements of the course. NOW, several ocean kayak, surfski and ICF boat companies are coming out with Unlimited class boats because there's a growing number of races and racers who are perhaps too big for an ICF boat, or want to go faster than a USCA boat or don't live near the ocean, etc... It's still pretty much a backyard business, but it's starting to take off.
In the MR340 crowd I see a microcosm of history repeating itself. When ultra distance paddling started, folks chose durable, stable boats that were fit for a long, drawn out expedition (see: pith helmets, wood crates, water boys, lamas, etc...). Now, we're looking at 260 to 340 mile races like a series of sprints needing lightweight materials. We're graduating up to more unstable boats and learning to stay stable in them because they're lightning fast compared to the more comfortable expedition sea kayaks.
My recommendation: get the tippiest boat you can stand, but not so tippy that you can't improve your paddling skills and fitness, comfortably. If that's a sea kayak, then that's just fine. HOWEVER, don't fall in love with it. As soon as you realize that your it's master and you can go faster in another boat, then sell it and trade up to a faster model. I always try to buy used boats because they're generally well cared for and flaws or damages are easily spotted. Much cheaper than new boats.
Learn to single blade AND double blade without using your arms. My lats were fried after the race Saturday, but my biceps, forearms, triceps and shoulders were just fine.
If you're stable in a surfski, like Ron's Epic, then I'd recommend an unlimited boat like the Spencer Extreme or the Landick. They're pretty stable, but fast in the right hands. You can single and double blade in them and store lots of gear, if need be. You'll shell out around 2800.00 new or around 1800.00 used.
Too much information? --West
You had a chance to see Texas unlimited boats in the 2006 MR-3400 Race: West Hansen paddled the DSX-canoe and I paddled Spencer X-treme. In 2007 MR-340, you will see again the DSX (Erin Magee) and Spencer Tandem Unlimited (Phil and Mary Jo Gumbert).
There is now a wide choice of unlimited racing kayaks available(i.e., kayaks not satisfying the ICF specifications). These include already classic kayaks designed by Doug Bushnell (West Side Boat Shop). You saw two WSBS Thunderbolt-X kayaks following West Hansen in the Fitty Gritty race. There are also some newer designs in this category like Kayak Pro Vampire or Van Dusen Mohican which is considered to be a cross between kayak and surfski. Valley Kayaks Rapier 20 is an example of a new generation sea racing kayaks.
Finally, so-called multisport kayaks are gaining popularity in USA, especially, among adventure racers. These kayaks originated from New Zealand are built for different skill levels and paddler weight. They are characterized by a rather small cockpit, but a high front deck not restricting leg movement. I paddle Sisson Nucleus 100 which is considered an intermediate multisport kayak. You may see Ruahine Ocean-X in the incoming MR-340 paddled by Ardie Olson.
Personally, I am always looking for some compromise between a boat speed and comfort which, in turn, depends on the race and your goals. I am not very comfortable in sea kayaks with a closed cockpit for a long distance paddling, so, I am biased towards kayaks with an open cockpit like WSBS T-bolt or a high front deck of multisport kayaks.
Of course, it is the best to own and paddle a variety of boats. A fast, light and demanding boat provides for me a great motivation for training and skill improvement. My 60+ lb Sea Wind is an ideal expedition canoe, but it is so much easier to take ultra light T-bolt or Sisson kayak for an 1 hour workout on a local lake, especially, since I have been using
Ez-Vee roof racks.