Land distances are well publicized and available from many sources. Distances by water are a little harder to determine. If you are in a human-powered craft, your route will be slightly different from that of a power boat. You'll tend to hug the inside bends on rivers, & take a much "shoaler" route in general. Depending on the draft (the depth of water required to float it) of your vessel, you may chart a course that includes the back channel of islands to save the time of going around it "the long way". This site doesn't really cover distances for ocean voyages, but if it did, there are other distance choices to make.

Most Navigation charts will give "sailing line" mileages. Of the sparse publications I have found, the U.S. Port-to-Port Distances publication has been most helpful. From it, I have created the following distance calculators, and will continue to expand on these in the future.

Distances Between United States Ports.....NOAA and U.S. Dept. of Commerce