As my first real woodworking project, I am building a classic Herreshoff pram in the British Virgin Islands (tough, I know). The ten-foot boat with transoms in the bow and stern will be light, planked with Northern white cedar milled to be 1/4" thick. The curved planks (strakes) will be bent over a series of rounded station molds hanging from a suspended ladder and then riveted together every 1-1/2 inches. The ladder has to be straight to keep each mold hanging exactly as intended by the lofting.

That is my problem: how can one ensure that the ladder will stay straight? The boat plans, taken from a book by John Gardner, "Building Classic Small Craft," recommends use of two, straight, 12-foot 2x4s each on edge and separated exactly 24 inches outside edge to outside edge by 1x4 cleats attached below the 2x4s and spaced every 15 inches. The molds will hang from these cleats.

We have very limited choices for lumber. Other than importing, everything is construction grade, and treated to prevent termites. Moisture content is high. While it may dry some, with huge changes in season (dry to rainy -- all with high humidity and wind), the wood will change. I own two suitable 2x4s but worry that they will twist, cup and bend over time as moisture continues to equilibrate. Positioning 21" 2x4s between the long 2x4s might help to reduce lateral bend, but what about vertical? I could also work with treated 2x6s but they are heavy and later I will need to turn the boat over. Any suggestions?