that every 2nd hatch may have to be due to having need somewhere to put the hatch whilst they load the hold then swap the 2nd, 4th etc onto the 1st, 3rd etc, the blunt question may have something to do with the submarine effect, the design of subs changed when the wave cutting design gave way to the more efficient whale shaped design as they moved from surface vessels to fully submerged. though I stand corrected.