Section 45.145 - Hatchway covers(a) Hatchways in position 1 and 2 must have weathertight hatch covers with gaskets and clamping devices.(b) The maximum ultimate strength of the hatchway cover material must be at least 4.25 times the maximum stress in the structure calculated with the following assumed loads: (1) For ships 350 ft or more in length, at least 250 lb/ft2 in position 1 and 200 lb/ft2 in position 2.(2) For ships less than 350 ft in length, at least AL in the following formula: (i) Position 1: AL = 200 + C
where C = 50(L-79)/271
(ii) Position 2: Al = 150 + C
(c) Hatchway covers must be so designed as to limit the deflection to not more than 0.0028 times the span under the loads described in paragraph (b) of this section and the thickness of mild steel plating forming the tops of covers must be at least 1 percent of the spacing of stiffeners or 0.24 in, whichever is greater.