def floatation_stability(W_sub, b, gamma_w=1.1) ->'float_stab_uty':
    """Floatation stability unity check. 
    Reference:
    DNVGL-ST-F101 (2017-12) 
        sec:5.5.5.3, eq:5.42, page:113 
    DNVGL-RP-F109 (2017-05) 
        sec:3.2, eq:3.1, page:12 
    """
    float_stab_uty = gamma_w * b / (W_sub + b)
    return float_stab_uty
