> If your not satified with the plans offered on the marked or if you simply
> love your old one and want to make a copy of it. Or, if you want to copy
> some parts of it and then develop the perfect hull. HOW DO YOU DO IT? If
> you don´t want to cut it in pieces? How do you transer the
> threedimensional existing hull to plans to be able to make a new one?
> Fritjof

Gil Gilpatrick, in his book on stripbuilding canoes has a discussion, with some pictures, showing how to take the lines off of an existing canoe. The process is the same for a kayak. Buy Gilpatrick's book for his views on how this is done. There are a few valid reasons for doing this. With old canoes, some of the classic designs are being re-done in modern materials, creating replicas. Sometimes those old designs (created without fancy computers) were very well done. When the companies go out of business it is still worthwhile to continue their ideas.

The general idea has been sketched out in previous posts. A few things I'd add or change:

Get the idea firmly in your mind that you ARE cutting the existing kayak into sections. The go about doing it without doing any damage. (No saws, please!)

What you want to produce are frames that can be used for new construction.

First decide how far apart you want those frames to be. If you are using cove and bead strips you can have the frames further apart. This saves you time and money on creating frames. Typically, frames are 12 inches apart (305 mm), or 18 inches apart (457mm). these are odd numbers in the metric system, so, since you are tracing things out yourself (and doing it from scratch) make it easy and pick a convenient spacing. An even 300 or 400 mm should be just fine.

Mount the original boat firmly to a strongback. This can even be the same strongback you will use to construct your new boat.

I have seen a strongback that uses a tight wire (or string) running down the center, under the frames, as a reference point. I like the idea. (Mark K. would suggest a laser. If you happen to have one on hand, why not.)

I have stretched a string down the center of my strongback and used brief sprays of paint to create a `shadow', defining a straight line that I use for reference. Others use a chalk line.

Line up your original boat so it is centered on this line. You want the bow and stern to be at least an inch or 2 (25 to 50 mm) above the strongback. You also want to be sure that the sheer line is just as high on the left side as it is on the right. You want it level, but upside down.

Building up two stacks of 2x4s at the cockpit, and resting the boat on those might be the easiest way to do the job.

It is pretty, but it does not matter if the boat's water line is parallel to the strongback. If you want to set it that way in order to give yourself a good visual reference, then do so.

You have one reference line under the boat, either a mark on the strongback, or a stretched wire or string. You'll need another one directly above that, which is also above the boat to copy. Nail sticks to the front and back of the strongback. Make them perpendicular to the strongback using a good square. Stretch a string between them. Adjust this string so that it is about an inch (25mm) or less above the hull at the center of the boat. The ends of the top string should be the same distance above the ends of your bottom string or mark.

Decided on how many frames you want yet? Find what looks like the center of the boat, or the widest spot. With asymetrical craft the widest spot may be forward or aft. You want a frame at this point. You work from here to the ends. Putting strips of masking tape on the boat allows you to make easily removable marks, when necessary.

The first frame can be made with several of the suggested methods. I'll have to try the solder method. I'd use strips of printer's rule material (thick strips of a lead alloy) instead. Art supply stores also have flexible lead (that's led, not leed) curves used by draftsmen which might also work.

Other ways that work are to scribe the shape onto sheets of posterboard or cardboard and measuring out coordinate points and redrawing the curves.

The fastest way may be to scribe the curves. It is basically the same method used to make bulkheads fit inside the hull. Some people use a compass or dividers. I'd make a tool from a small block of wood and a pencil or felt tip pen. Drill a hole in that block of wood big enough for your pencil or pen. When you slide this gadget over the hull the pen or pencil point will remain an even distance above the hull at all times. Keep the cardboard straight up and down(use a level) and place it where you need a frame and use this gadget to trace the outline on your cardboard. Cut out the shape you have drawn and test this by holding the cardboard against the hull. Use the strings to determine the alignment at the top of the form.

You can also use a cardboard or wood rule marked at 2 inch ( 50mm) intervals placed a fixed distance from the center lines ) maybe 20 inches or 500mm. Extend a straight edge in from that rule until it touches the hull and measure that distance. Use these numbers and measurements to create a graph-like drawing of dots which you will connect to re draw the hull curves.

If you have a string at top and bottom you don't have to float the boat to get a waterline for determining rocker. Comparing measurements from the center of the boat to the ends will indicate how much rocker is present. If the center is 25 mm from the string and the ends are 75mm from it, then I'd guess you have 50 mm of rocker. If you want more, or less on YOUR boat, you can always mount your new frames higher or lower.

The very front and back (bow and stern) are built around forms that run in line with the boat. Use the wires or strings to determine the height and shape. Trace or scribe onto cardboard, or use measuring jigs to determint points to plot.

Depending on the shape of the hull near the ends you'll have to decide when to quit using hull cross sections and when to start the forms for the ends. You could probably put frames based on the cross section to within a foot (300mm) of the end, but with some designs you dont even need those narrow forms. Most of the time your strips can just bend naturally over a 2 foot (600mm) span between the last crosswise form and the lengthwise end form.

Notes:

When fitting and scribing the cardboard, or measuring points, you only have to do one half of the hull (left half or right half) Flip the pattern at the center line for making the lines for the other side of your boat.

Remember that you are measuring the OUTSIDE of the hull, and if you make male forms they will conform to the INSIDE of your boat. If you are using 6mm (1/4 inch) strips your boat is going to be 12 mm (1/2 inch) wider at all points than your prototype. So, decide how thick your strips will be and adjust your measurements (or drawn or copied curves) by that amount plus a fudge factor of 2 mm (or nominally 1/16 inch) to compensate for the thickness of the fiberglass and resin.

There are some people who use female molds to constuct their boats. I haven't tried it, but it appears to be more difficult to do it that way. If you do this, though, then you won't have to compensate for the strip thickness.

There are also people who measure the inside of the hull. This is a lot easier with undecked canoes than with kayaks, but if you have a boat where the top can be removed, it is an option.

If you trace or scribe the forms you will need to know how high to mount them. make some alignment marks on your cardboard and measure from your strings to get the proper height.

You may want to make your forms 2 to 4 inches taller than your measurements. As long as you raise everything equally this is fine, and gives you more room to work above the strongback.

If there are areas where curves change rapidly, measure and place an additional form. There is no particular magic in having evenly spaced forms. It is just easier when you are working from plans -- and here you have no plans.

Essentially you are creating a 3 dimensional plot, using a centered baseline as one axis. You measure along the length of this line to find the placement of your frames. At these points you measure above it, and to the side to locate points on the outside of the hull. When you reconstruct these points you have a hull.

You may want to simplify things a bit by making your deck from scratch. This is one less thing to copy, and should not affect the performance of the craft unless you go very far off. Typical decks are just based on even curves of a nominal radius. A radius of 1.5 m (60 inches) is pretty good. Make some deck beams to that size, and install them as a base for the deck and as strengtheners (like thwarts on a canoe) for the hull. A plywood deck can be quickly added to a stripped hull, or for that matter, you can quickly lay strips over those deck beams and not bother about making plywood forms.

If you are planning on installing bulkhead, use one of the patterns for a form and make two copies. The first is the plywood frame, the second is the plywood bulkhead. You can stack your material and cut both at the same time, using better (or at least prettier) material for the bulkhead.

Hope some of these ideas help. Paul Jacobson