In discussing the optimum size of a passagemaker and looking at the role of ballast, a related area is the degree of comfort as it is affected by motion and the parameters controlled in the design process. While ballast and hull form will affect the initial and ultimate stability of a vessel. All of us have likely experienced vessels that have a snappy, uncomfortable roll, or those that have a long, slow, miserable roll that makes you wonder if you'll survive a substantive beam sea. I once went out on a new $40 million 150 foot yacht whose Captain would not leave the dock without the stabilizers on. In the latter case the owner could not understand why we didn't want to put a 4 ton submersible on the flying bridge deck. The optimum natural roll period of a vessel is 1.0 - 1.1 times the beam in meters. A roll period of less than that will be too snappy to be comfortable while one more than that will have you wondering if she's safe. The second comfort factor is the degree of heave, or vertical acceleration. This is dictated by a relationship between displacement and overall buoyancy at the waterline (e.g. waterplane area). This number, the waterplane loading, is optimum below certain values that vary with displacement. I've had two sailboats in my past, a heavy, beamy 45' Hardin ketch and a much lighter Beneteau 38' foot sloop. The Beneteau was sleek and relatively fast but most of the family couldn't stand to be below in any kind of sea until we had been cruising for a couple of days. The Hardin's motion was a delight in most conditions. Bruce -- ======================================================================= L. Bruce Jones U.S. SUBMARINES, INC. President POSEIDON UNDERSEA RESORTS LLC Tel: 208/687-9057 Fax: 208/441-7478 E-mail: bruce@ussubmarines.com http://ussubs.com http://poseidonresorts.com "Design, engineering and construction of submarines and submersibles" "Submarine related consulting, sales and operations." =======================================================================