The safest and fastest cats for ocean passages will feature moderate freeboards, high underwing clearance, low bridge-deck cabin height and moderately broad beam. Many designs are available only on a custom or semi-custom basis, but most of today's production cats combine satisfying, often exhilarating sailing with spacious and comfortable living aboard. Although the boat's maneuverability and stability are ruled by the spacing of the hulls' centerlines, overall beam measurements are more widely available and can be used for comparisons. However, there is a point when the boat becomes less stable longitudinally or diagonally than athwartships, so there is a balance. Bridge-deck underwing clearance forward is vital, but it is important throughout the length of the bridge deck.
Clearance is less of an issue in flat water, but offshore it is imperative for comfort and safety.
Waves slamming underwings have damaged many boats. Wider-spaced and longer hulls span more ocean, allowing swell and chop to affect the underwing more and demanding more wing clearance. Many boats use complex curves under their wings, which helps to dissipate any slamming and excess loads. Multihulls appear as ugly boxes to some sailors while others think they are as elegant as seabirds. One catamaran aficionado wisely directed his designer to draw up a boat with a typical 50-footer's accommodations, then make the boat 65 feet long.