Unsymmetrical flooding is to be kept to a minimum consistent with efficient arrangements. Where it is necessary to correct large angles of heel, the means adopted shall, where practicable, be self-acting, but in any case where controls to cross-flooding fittings are provided they shall be operable from above the bulkhead deck. For new class B, C and D ships the maximum angle of heel after flooding but before equalisation shall not exceed 15°. Where cross-flooding fittings are required the time for equalisation shall not exceed 15 minutes.