double Boat::DisplacementLongTons()
{
    return DisplacementPounds() / 2240.0;
}
/* values greater than 2 are a danger, less than 2 is "good" */
double Boat::CapsizeRisk()
{
    return beam_ft/pow(1.1*DisplacementPounds()/64, 1.0/3);
}
/* values of 30-40 for cruisers, 20 or less for racers, higher for
   heavy boats */
double Boat::ComfortFactor()
{
    return DisplacementPounds() / (.65 * (.7*lwl_ft + .3*loa_ft) * pow(beam_ft, 1.33));
}
double Boat::SailAreaDisplacementRatio()
{
    return sail_area_ft2 / pow(DisplacementPounds() / 64, 2.0/3.0);
}