Although I do not have a lot of experience with the copper coil kind of engine, I can point you to some very good instructions by others.
Yvon Masyn
This gentleman from Belgium, Yvon Masyn, has done a wonderful job of creating a simple design that young kids can participate with.
Marc Horovitz
We can thank Marc Horovitz for these high-quality, illustrated instructions for making a complete coil-type boat with recycled tin sheet.
Dr. Guus Flogel
My friend from the Netherlands Dr. Guus Flogel has written the ultimate guide for building a boat with a coil engine out of a wooden Dutch shoe! He has also done the experimental work to determine what size works best and how many coils should be made for best results.
Bob Jay
One of the biggest hassles has been finding the right size of tubing. Bob Jay seems to have solved the problem for people who have a PepBoys (automotive store) nearby. As he wrote me,
"Here's the skinny on the copper tubing . At two local Pep Boys there is a large section of an isle dedicated to various auto parts called " HELP ". They are on red cardboard with the part in plastic blister heat shrink. The red pack has the word " HELP!" in white letters. The tubing that I used is 1/8" x 8'. The HELP number is 55134 and the SKU # 37495 55134 2. I hope this helps ya out."
Thanks Bob. Another thing I think is worth pointing out is that copper can be annealed (softened). This is important because bending hard tube results in kinks (which block the tube) rather than smooth bends. Strangely, copper is softened in exactly the way that steel is hardened--by heating to red hot and quickly quenching in water. As copper is worked (bent, for instance) it once more starts to harden. It might have to be annealed again. The procedure is explained in both Marc and Guus' articles.