Well, Jack, let's see how my math is...
If 1 inch real measurement = 7 feet scale measurement, that means
1 inch real = 84 inches scale or 1/84 scale
Since 1 divided by 84 = .0119, divide any distance on the model by .0119 to get the real 1:1 size.
For example, if the mast is 3" tall, 3" divided by .0119 = 252" or 21 feet.
This also works in reverse:
If you need to make a part for the model that is 8 scale inches long, multiply it by .0119 and the part needs to be .0952" long (or just under 1/10").
Hope this helps.
Enjoy your modeling...