The table below will calculate the number of ribs allowed (based on 1:144 scale ship models and 15% penetrable length) and the amount of solid area desired at the bow and stern

Select a Ship:
Enter Solid Areas:
at BOW: inches (2 inches max)
at STERN: inches (1 inches max)
Select Rib Width:

Calculations for a Abdiel-class warship 418 ft long (34.83 inches scale)
15% Impenetrable (solid) Area: 5.22 inches
Solid Bow Area: -2.00 inches
Solid Stern Area: -1.00 inches
leaves 2.22 inches for ribs

Using 0.25 inch ribs will allow for 8 ribs along the length of the hull
(and one rib may be 3/8 in wide, or one additional 1/8 in rib)