Since the XTs are our newest kayaks, I will give you a quick tour of the design process. The real process took a couple of years - and countless sketches on napkins, with some computer simulation added for good measure.
To make a kayak like the XT, a completely new frame structure had to be invented. The challenge was to make a long and sleek folding kayak with excellent stiffness. In other folding kayaks, the designers often rely on a deck structure to give the hull enough depth to enhance stiffness. We wanted to be independent of the deck. The solution turned out to be 6" wide I-beams along each side of the hulls.
Conceptionally, adding I-beams is simple enough, but implementation was a challenge. The I-beams had to fold up and pack into a compact package, and they had to be rigid once assembled in the boat. That means that all the joints have to be absolutely solid, and the forces involved are considerable. A number of ideas were proposed and discarded until Ralph came up with the concept of attaching the locking system to each cross rib. Stainless steel pins fit into matching holes in the top and bottom joints of the I-beams and keep the joints solidly together. One pin is fixed to the top of each cross rib, and another to a lever that snaps into place against the cross rib. This locks I-beams and cross ribs together in a solid and lightweight frame.
Unlike other Pakboats where longitudinal skin tension is built gradually as the frame is assembled in the skin, XT frames are built outside the skin, so a new tensioning system was required. We tried and discarded ratchets and finally settled on a lever system built into both stems. The levers transfer tension to the I-beams and push against the ends of the kayak skin.
The kayak skin needed some work too. With the I-beam frame, we no longer have simple gunwales that can be inserted into channels. Instead, we wrap the top of each side of the skin over the gunwale and secure the sides to the frame with cord loops.
Tightening the skin sideways is a familiar operation. The XTs have inflatable tubes like the other Pakboats - the slimmer style that we have used in PakCanoes. Inflating the tubes makes the skin nice and tight. Not much new design work to do here - except that we tapered the ends of the tubes to get the sharp entry lines of a high-performance touring kayak.
The XT decks are very different from decks we used to have on the Puffins (but a simplified version of the new XT deck has migrated back to the Puffins). We wanted to have the XT decks solidly supported and at the same time be able to change seat positions freely so an XT could be used both solo and double. The solution turned out to be a deck support structure built into the deck itself. No part of the kayak frame is intended to support the deck, so the hull can be completely open. The cockpits and seats can be placed without regard to any part of the frame. While we were at it, we made the cockpits longer to make it easy to get in and out of the XTs (or Puffins). To minimize assembly time, we wanted to leave part of the support structure as well as the back band and (optional) thigh straps permanently attached to the deck. This required adding a flap on each side under the deck fabric to attach accessories.
XT seating was a challenge. We wanted a seat that would be suspended from the sides and not touch the bottom fabric. It should be very comfortable and easily packable - and not put undue stresses on the frame. The result is a sling type seat suspended front-to-back in a frame that rests on the chine rods. On top of the front support is an inflatable adjustable thigh support. The back band can be adjusted independent of the seat. We are very happy with the result!