Illustration:
Example for a comfortable ride with waterproof box on top of board.
John 75kg, 1.80 m, shoulders’ width 60cm (0.6m)
V = (75 + 30) x 1.1 = 116 L= 0.116m3
W = 70 cm = 0.7m
T = 0.116 / (1.8 x 0.70) = 0.092 = 9.2 cm
Nose bevel: board top length = John’s height = 1.8 m
Board bottom length = 1.8 x 0.8 = 1.44m
For a comfortable ride with waterproof box inside the board (box dim = 30 x 20 x 10cm = 6 L)
To preserve board structural strength, you have to add a minimum of 2.5 (1") cm of EPS foam under the box.
So new board thickness = Box thickness + 2.5cm. (1")
In the above example, new T = 10 + 2.5 = 12.5 cm
New board volume = (1.8 x .7 x 0.125) / 1.1 = 143 L - 6 L (box volume) = 137 L with nose bevel (hence /1.1)
So adding a 6L waterproof box adds 21L to original board configuration with box on top.