When you have your boat making patterns that look right in the water, figure out how fast it is actually going, guess how fast the real thing would have been going, and you will find that the square root of the scale rule is involved. Test tank users have been using this for donkeys years. It also works the other way, knowing the performance of the original and dividing by the square root of the scale will tell you how fast it should be going to look right in advance.

45kt about 60mph = (60*5280)=316800ft/hr, (316800/3600)=88ft/sec,

scaling, sqrt72 near enough 8.5, (88/8.5)=10ft 5in per second.

If I take my 1//72 boat for a walk around "my" lake, its 1 real mile. The boat has cruised a scale, linear 72 miles. If I take an hour, it will have looked like it was cruising at about 8.5 mph. For the crew, they will think that they have been out for 8 and a half hours. No mysteries, everything is nicely accounted for.