Hi Tony,
What drawings are you using? Endurance did not have metal sheathing at the bow but rather it was specially constructed to withstand ice encounters with a bow made of oak timbers with a cumulative thickness of 52" according to one source. The Endurance Conservation Management Plan in section 2.1.1 states that the maximum hull thickness was 30 inches. It does not state if the bow was thicker though. You may want to contact them and ask about the now timber thickness.