How big must the coxswain's cockpit be in a bow-enclosed boat?

In a boat with an enclosed bow coxswain's position, the opening must be at least 70 cm long and as wide as the boat for at least 50 cm. The inner surface of the enclosed part must be smooth, and no structure of any sort may restrict the inner width of the coxswain's section. The rule is there to avoid accidents arising from capsizing (RCA Rules of Racing, rule 3.6).