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)
The Swan 36 is the boat that kicked it all off for the prestigious Finnish yacht maker Nautor’s Swan, a name recognized among sailors as makers of some of the best production boats built. Its founder, Pekka Koskenkylä, way back in 1966 approached the hallowed New York design firm Sparkman and Stephens while they were working on some design projects in Finland. Koskenkylä’s idea was to build a yacht in the 10 metre range that would be strong, seaworthy and fast enough to be suitable not only for cruising but racing as well. He wanted to utilize fiberglass molding techniques which were still in its relative infancy at the time.
The outcome of the agreement was Sparkman and Stephens design number 1710.51 which was a hull form already being used in boats being built by Cantieri Benello (Gaia Class), Cheoy Lee (Sigma 36, S&S Design #1710.8) and by Chantier Bertin in France. Where the Swan 36 design differed significantly was the use of a separate rudder from the keel, quite an innovation for its day and a configuration for which Sparkman and Stephens was having great success with in their Americas Cup designs (in 1967 and 1970 their separate rudder 12m boat -Intrepid_ went on to claim successive defense victories.)
With her departure from a full keel, the Swan 36 stands somewhere between the classic and a new generation of design thinking. She still retains moderately long overhangs and a deep bilge yet her hull has a pronounced tumblehome with a pointed diamond shaped plan profile which was becoming popular in RORC racing designs of that era. Her interior layout was simple and functional.
She was introduced in the spring of 1967 with the first Swan 36 delivered to British sailor Dave Johnson, whose racing successes around the UK generated a good reputation for Swan as a maker of performance racing yachts. Notably, in 1968, Casse Tete II won seven wins out of seven at the Cowes Week regatta. As the Swan 36 continued to impress on the racing circuit, owner feedback and wish for improvements propelled Swan to produce the Swan 37 in 1970, the same year the Swan 36 production ceased with a total production of 90 boats.
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