Wait a minute. Before folks start lining up for free work let me admit; yes, this is a trick question. Good design saves construction time and wasted materials. If you are building the boat yourself and you don’t count your time, then maybe additional weeks don’t count. Pay a boatyard, however, and you will see that construction time adds up quicker than drawing time. The old bromide is really true… "It’s easier (and cheaper) to change something on paper than to change it in real life." In this respect good design will save you more money than it costs.

Nice platitude, but how many real dollars are going to leave my pocket in getting a boat designed? The question that should be asked is how much should be spent. What is the balance between design money spent and value received? A reasonable design cost is roughly 5% of the building cost of the vessel at a commercial yard. An excellent yard may need less information. Another might require much more. There are minimums, however below which construction is risky.