: I was planing to build a Kayak from Lexan I've done some glue test and
: everything holds fine. I had not planed to paint the craft but leave it
: clear. What do ya think? Any comments or advice will be appreciated.
: Thanks.

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.