The reasons for the deviation:
- Keel - A laminated keel will be less prone to expansion / contraction and therefore less likely to split under hard use. Bottom line, the boat will last longer.
- Planking - By laminating mahogany over the plywood skin, I can finish the boat in a natural wood tone instead of painting it.
What this means to the lumber purchase plan is that I need to order different thickness plywood for the planking and order additional material for the second layer of mahogany. The keel will also be a different thickness which is a further change of the materials listing. And finally, depending upon the lengths and widths of material that I can get, I can layout more pieces of the boat on fewer pieces of raw lumber, therefore reducing the quantity of the lumber I have to buy. Since marine grade lumber is quite expensive this is a desirable outcome.
So the plan is an exercise in calculating how many different pieces I can get on any given piece of lumber, how many pieces of larger lumber can be cut down to get the smaller sizes I need, alternatives depending upon what lengths and widths are available, and finally which lumber I need now and which lumber I can delay purchasing if the cost exceeds my current budget.
I am about half way done with the plan right now. I've determined that calculating the lumber requirements for the frames is going to require additional work in determining how big each frame piece is so I've devised a document defining each frame piece and I will be using the plans to determine the rough cut size of each piece and then adding those dimensions to the document. When completed, I can use this document in a similar manner to the materials listing to calculate lumber requirements for the frames.
Sorry for the long winded post. As a hobbyist, I sometimes get carried away with the details and its hard to contain my enthusiasm.