The actual lofting process is a matter of draftsmanship, parts of which have been simplified by computer drawing programs. For a complicated shape this is step two in the process. First you need a really good picture or a model. The model would be my first choice.

You don't have to work to any particular scale, but if you try to make the model 1:12 or 1:10 you'll probably save some time later when you enlarge it.

If you want a pretty close knock-of of that zaby, which has the specs listed on their website in metric, work with a 1:10 model. shift the decimal place, and the 5 meter boat becomes a 0.5 meter ( or 50 cm) model. That is about 20 inches long, which is small enough to work on inside on a cold winter night.

You can make the model from a soft wood like cedar, redwood, or balsa, or you can use a block of plastic foam, or a lump of modeling clay or plasticene.

If you work with clay, or foam you can make a plaster mold around your model, then use that mold to make a plaster replica of your design. The plaster won't change shape by being touched, like plasticene can do, but it can still be shaped if needed.

If you make your model from a finegrained plastic foam, such as those sold at art stores for sculpture, Dick Blick has a housebrand for a reasonable price.

http://www.dickblick.com/zz331/14/products.asp?param=0&ig_id=1973

Compare this with their balsa foam II, and regular balsa foam.

http://www.dickblick.com/zz331/11/products.asp?param=0&ig_id=1974

http://www.dickblick.com/zz331/11a/products.asp?param=0&ig_id=30

Once you have a wood model you can slice it on a table saw at regular intervals so you can measure it for making forms. With a foam model you can cut it with a hot wire, or a table saw.

If you don't want to bother with redrawing things, you can cut your model at 3cm to 5cm intervals, corresponding to 30cm to 50cm (roughly a foot to 20 inches) in real size, and simply lay the cut pieces on a photocopy machine and enlarge them to life size.

Carving some alignment marks in the edges before cutting the model would help when aligning the building forms. Set an Xacto knife, razorblade, or utility knife a small distance above your table, and slide the model along the cutting edge, putting a neat thin cut into the model at an exact distance above your worktable. When this is enlarged it will show up as a nice alignment mark.

If you don't want to cut your model you can make a jig with a series of steps, or a set of blocks, which rise above the height of your table in increments of 2mm to 3mm. Slide these "steps" next to your model and use calipers resting on each step to measure the width of the model. This way you get a series of numbers which would be similar to height above the worktop (which you would use as if it were height above waterline when drawing your forms. For example, if you are measuring 10 cm from the back you would set these steps alongside the model and measure the widths. with a block 12 mm from the surface you might get a width of 25mm. The next taller block would be 15mm high, and the width might be 27 mm. the next block would be 18mm high and the width might be 26mm. The next block would be 21 mm high and the width might be 24mm. You could then graph these points using the height of each block (12,15,18,21mm) times 10 to give a life sized 12 cm, 15cm, 18,cm and 21 cm height, and the measured widths would be correspondingly multiplied by 10. Graph the width and height and connect the dots. If you want more detail in your graph, flip the model on its side (90 degrees) and remeasure it along the center line and at fixed distances out from that point. Add those numbers to your graph and the line is practically in front of your eyes.

If the Zaby design is something you are going to use as a starting point, photocopy the drawings they have on the website and enlarge them to whatever scale size you are working at. Trace the outlines from these on your block of wood or plastic (or jsut glue on the photocopies) and you can cut along the lines to roughout the shape of the model on a bandsaw in a matter of a few minutes. A plane, drawknife or coarse sandpaper will get the rough shape closer to your design.

Just a guess, but I'd go with 3/16th strips and 6 ounce fiberglass on both sides. The thin strips would flex easily to get them in place during construction, and the heavier glass would give you the strength. Internal bracing of 3 or 4 evenly spaced wood ribs (about a 3/4 inch to 1 inch crossection should do -- 18mm to 25mm) with 3 layers of 6 ounce glass over them will provide more strength should the iceboat flip over. You can add these after you do the stripping, or you can cut them first and use them as your building forms.

Good luck with your project.

PGJ