On this one, (first try) I only used a single ply layup. Next time I will do a double ply which add a lot more strength, and the edges between strips don’t have to be so critical.
You want to lay up the veneer on a bit of diagonal, because it bends and conforms to the compound shape of the hull much better. Remember with a rounded hull, you wind up with compound bends, since you are bending a curve (Gunwales to keel curve) and at the same time you are bending the other way for the rocker of the keel. Simply use a piece of paper and you will see that it bends easily in one direction or the other, but not both ways at the same time. Place it on a diagonal, and it bends both ways.
I’m sure Will or Dan can give the engineering reasons “why” - I just know it does. Same with placing glass fabric over the outside of a hull (use existing boat and just lay a 4 inch wide strip of paper over in about the same location as my birch strip) - you will find the cloth will layout and conform to both directions if it is placed on the diagonal so threads (warp and weft) cross the hull at about a 45 degree angle to the keel. If you turn so one set of threads crosses at 90 degrees, you will find it has a tendency to pucker if it isn’t going across a straight line of the keel. Obviously if you lay up 2 layers of veneer, at opposite angles, you begin to get strength like you do from plywood.
Veneer that I used, comes on a roll at Home Depot/Menards/Lowes and has iron-on adhesive on the back. I used an iron to “tack” the veneer to each of the stringers, but then went inside and brushed on a coating of epoxy just to make sure the veneer adheres to the stringers! The roll comes 2 inches wide x 8 feet long, and for the Mistral it took 2 rolls. They were on sale at $2.50/roll when I saw them and bought 8 rolls. Normal price is probably around $4.00/roll.
If you build stringers and set them into the shadow templates, you can strip with balsa in the same manner, and you don’t have to taper any of the strips. Just lay them at an angle to the keel between 45 and 60 degrees. If the balsa edges are straight, you can edge glue. Building this way eliminates the ends of the strips that have to be tapered to fit the curve/bend of the previous strip. Just start up near the bow and hold the strip in place at an angle that you like, and where the strip lays flat. Keep in mind, that after you are done, if you want a “bright” (clear) finish, you have to think ahead in which direction you lay up the strips. I think (personal opinion) I like the strips to start near the gunwale and angle back, down and around to the keel. If doing a double cold-mold, remember to reverse your first layer as the second layer will cover the first!
Because you don’t have to steam or heat the strips to bend them to lay flat against the stringers, it is an easy, non-messy process and building time goes quite fast. Also you can glue with out waiting for strips to dry first if they were wet or steamed. That why it is referred to as “COLD” mold. Many, many plywood outboard runabouts were production built this way during the early to mid 1950’s. If you want to get real fancy, you can special order custom veneer made from exotic wood species.
I have a piece of “bananna wood” veneer that I bought for a deck of a 1 Meter. Didn’t use it all, so have a bunch left that I keep eyeing. It is 12 inches wide x 8 feet long originally, so I can experiment with just how wide of strips I can layup on this little hull. Just think, if you can layup (on the diagonal) a piece of veneer that is 5 inches wide by 6 inches long you have just covered 30 sq. inches of hull surface with a single piece of veneer. Mighty fast build - compared to 1//4 inch wide or smaller strips. Only a layer of fiberglass is faster.