The theoretical maximum speed that a displacement hull can move efficiently through the water is determined by it's waterline length and displacement. It may be unable to reach this speed if the boat is underpowered or heavily loaded, though it may exceed this speed given enough power. Read more.
Classic hull speed formula:
Hull Speed = 1.34 x √LWLA more accurate formula devised by Dave Gerr in The Propeller Handbook replaces the Speed/Length ratio constant of 1.34 with a calculation based on the Displacement/Length ratio.
Max Speed/Length ratio = 8.26 ÷ Displacement/Length ratio.311
Hull Speed = Max Speed/Length ratio x √LWL
A measure of the power of the sails relative to the weight of the boat. The higher the number, the higher the performance, but the harder the boat will be to handle. This ratio is a "non-dimensional" value that facilitates comparisons between boats of different types and sizes. Read more.
SA/D = SA ÷ (D ÷ 64)2/3
A measure of the stability of a boat's hull that suggests how well a monohull will stand up to its sails. The ballast displacement ratio indicates how much of the weight of a boat is placed for maximum stability against capsizing and is an indicator of stiffness and resistance to capsize.
Ballast / Displacement * 100
A measure of the weight of the boat relative to it's length at the waterline. The higher a boat’s D/L ratio, the more easily it will carry a load and the more comfortable its motion will be. The lower a boat's ratio is, the less power it takes to drive the boat to its nominal hull speed or beyond. Read more.
D/L = (D ÷ 2240) ÷ (0.01 x LWL)³
This ratio assess how quickly and abruptly a boat’s hull reacts to waves in a significant seaway, these being the elements of a boat’s motion most likely to cause seasickness. Read more.
Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam1.33)
This formula attempts to indicate whether a given boat might be too wide and light to readily right itself after being overturned in extreme conditions. Read more.
CSV = Beam ÷ ³√(D / 64)
Following in the hallowed footsteps of the original Seawind, a salty 30 foot ketch designed by Tom Gillmer that happened to be the first fiberglass sailboat to circumnavigate the globe, the Seawind II is a larger, more comfortable redesign that’s a foot longer, a foot wider, and over 23% heavier. These boats were launched in 1975 by Allied Yachts and they had a reputation for being solidly built, though with a history of inconsistent and uninspiring internal finishing. The company went out of business four times, before finally shutting down for the fifth time in 1981, spelling the end of production for the Seawind II.
Allied Yachts was founded in 1962 on the Hudson River a hundred miles north of New York City in the small town of Catskill as a partnership between a fiberglass boat builder Lunn Laminates and a yacht brokerage of Northrop and Johnson and racing sailor Thor Ramsing. Their first boat, the Seawind, a popular 30’ 6” ketch had the company busy keeping up with demand.
These were still the exciting pioneering days of fibreglass sailboat construction when the material was still considered experimental and hulls were conservatively built extra thick. When New Yorker, Alan Eddy, setoff in 1963 to eventually circle the globe in Apogee, the accomplishment did much to not only put to rest skepticism over fibreglass construction, but also to establish Allied’s reputation for building seaworthy sailboats.
Despite the original Seawind proving itself as a competent bluewater sailboat, it had minimal accommodations that were, at best, cramped. So after over a decade of successful production of the Seawind, Allied approached Gillmer to evolve the design into a successor – the Seawind II. Though it was only 13 inches longer, its beam was 13% wider which resulted in a displacement 23% heavier. The result was a much more comfortable boat with significantly larger internal volume and improved accommodations.
Structurally the new boat was just as sturdy and had improvements over the original construction. The hull was hand-laid and substantially thick and well supported bulkheads that were fiberglassed into place. Furthermore the hull-deck joint, which was prone to leaking in the original Seawind was improved with no expense spared. The new joint was complex, labor intensive to construct but very strong. Both hull and deck had outward flanges at the sheer line. These flanges were coated with sealant and a teak batten placed between them. Hull, deck, and batten were then through-bolted vertically with stainless steel bolts. After the sealant cured over a number of days, the joint was ground flush on the interior of the hull and glassed over heavily. Meanwhile on the exterior a heavy aluminum extrusion was filled with bedding, capped over the flange, and horizontally screwed into the teak batten.
The deck and cabin were of fiberglass cored in balsa wood. All deck hardware was through-bolted and reinforced with fiberglass backing plates to distribute the load. The mast was deck-stepped and supported from below by a substantial oak compression frame that extends into the bilge. Ballast is an internal lead casting glassed into the keel.
There’s very little exterior wood on the Seawind II, even the dorado boxes are molded in, resulting in a low maintenance boat, but also gives her an austere look.
Unusual to see in a sailboat this small is a ketch rig which was offered as standard, there was an optional cutter rig which carried slightly less canvas but had similar performance. As to be expected, Seawind II sails well under heavy sea conditions, but perhaps surprisingly it’s quite competent in light weather as well. She has a very comfortable motion at sea, is well balanced with very little signs of weather helm.
Overall the Seawind II today is a practical and affordable choice as a go-anywhere cruiser. She’s strong without being overly heavy, well constructed and proven. Many examples on the used market have held up well, with later models generally having better finished interiors.
» Seawind II owners association website
» Sailing Magazine, Feb 1999, Used Boat Notebook by John Kretschmer
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