: Sounds like fun. I made a lexan windshield for a motorcycle many years ago.
: The material cuts with wood tools, but be careful to avoid chips on the
: edges, as they reduce the amount of bonding area and look ugly. In most
: regards it is like plexiglas or other acrylic plastic sheets, but you can
: score plexiglas and snap it on the scored line, and I'm not sure if Lexan
: would be so willing to do that.

: I assume you are using a solvent to weld the edges, and not a
: "glue". I think Methylene chloride or Ethylene dichloride are
: the solvents, but you will want to check with the supplier. Solvent welded
: joints are just about as strong as the material itself, but the angle at
: which the parts meet at the joints can cause stresses to concentrate.

: If you go with 1/8th inch material the boat is going to be very flexible. If
: you go with 1/4 inch material the boat is going to be heavy.

: Clear lexan expands and contracts a lot more than plexiglas with changes in
: temperature. A type of lexan which is reinforced with chopped glass fibers
: is more stable, but somewhat translucent. The local railroad used clear
: Lexan for windows in some stations where vandalism was high, and the
: panels were mounted in special tracks so that there was about 1/2 inch for
: the panel to expand and contract with changes in Chicago weather (plus 1/4
: inch and minus 1/4). That is for a window about 40 inches wide. Your boat
: will probably be about 4 1/2 times longer than this, so if their design
: means anything, be prepared for the boat to expand an inch or contract an
: inch over its entire length, over winter and summer conditions. You may
: not paddle when it is below zero, but your boat may be stored in those
: conditions. Should the boat sit under a hot sun for an afternoon you'll
: have the opposite effect.

: This is important if you have parts made from different materials (say a
: metal, or wood seat track with foot rests) which run length-wise and
: probably won't expand and contract as much as the plastic. So mount them
: in such a way that they can "float" in the mountings, and avoid
: stressing the plastic.

: I'd reinforce the seams with chine strips of Lexan. Or, look at the
: overlapped lapstrake construction used in "Ultralight
: Boatbuilding" by Thomas J. Hill.

: Your biggest concern is going to be the precision needed to make 16 foot long
: joints that are very closely fitted. You'll probably need some forms and a
: strongback to hold your panels. With the methods I've seen for plexiglass
: construction, which should be similar, you clamp them tightly so there is
: no discernible gap. The solvent is applied to the joint and it seeps in by
: capillary action. If the gap between the panels is too large the solvent
: won't get there. Thickened glues and fillers consisting of small
: quantities of the same plastic dissolved in solvent can be used to fill
: the gaps.

: With Hill's construction method the forms, and wood chines attached to them,
: serve as guides for cutting the panels of plywood he uses. You would
: simply substitute 1/8th inch Lexan for his 1/8th inch plywood. Hill's
: books hows how he uses the framework as a guide for his plane. He dresses
: down the inner piece of plywood and lays the adjioning panel so that it
: overlaps the area he has machined. With numerous clamps he draws the
: panels together while his glue sets up. In your case you could see through
: the upper layer and watch as you clamped things together. You would have a
: large glue (solvent) area -- maybe the panels would overlap by an inch or
: more -- and you could apply glue from either inside or outside. The areas
: where the panels overlapped would give you a thickness of almost 1/4 inch,
: and provide stiffness and strength, just like chines provide that service
: in skin-on-frame kayaks.

: If you don't like Hill's method of building, consider the Putz design, or at
: least his construction methods. You build the forms, mount a chine at the
: corners, and machine it so that the edges align with the angles where the
: panels meet. With this, or with Hill's method, I'd use a router or an
: electric plane, rather than hand tools, and mount them as Hill shows. Once
: I had one edg of the chine cut I'd lay the panel on, overlapping the chine
: slightly, apply a copious number of clamps (probably I'd make these from
: PVC pipe with duct tape over the slit edges so they wouldn't bond to the
: boat should they come in contact with the plastic solvent) Then, after the
: solvent had fused these pieces I'd machine the second edge of the chine,
: cutting off any overlap from the first panel. When this was done I'd glue
: on the second panel. Fitting this edge would be trickier, but I'd let it
: overhang a bit, and cut off the excess later with a router and a laminate
: trimming bit. Clamoing this edgw would be more difficult, but I think you
: could use a combination of duct tape, bungie cords, and weights to hold
: the panel tightly until the solvent had fused the panels and evaporated.

: Be careful with those solvents. They are not kind to human physiology. Work
: with plenty of ventilation, and wear the proper respirator mask.
: Fortunately you use only small amounts of solvent if your joints are well
: formed, and it evaporates fairly quickly. The smell doesn't linger very
: long -- a few hours.

: Good luck if you decide to pursue this project. It sounds "do"
: able.

: PGJ

: One other thought. With most kayaks it doesn't matter what swim suit you
: wear, but in this case you would want to wear something bright and
: attractive, as people will have a good look at it.

Oh, don't forget lots of suntan lotions.