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 Westsail 28 is the smaller sibling to the incredibly successful Westsail 32, a boat that captured the imagination of the American public with the “cruising life”. By the mid in 1970s when demand for the Westsail 32 was in overdrive, the pricing had crept up enough that Westsail needed a new boat to fill the entry spot. The Westsail 28 was launched to fill this in 1975 and was described as “a hearty little offshore cruiser perfectly outfitted for 2 to 3 to cruise trouble free around the world”. The boat made a number of appearances to boat shows along the West Coast and was offered as a complete build ex-factory and later also in kit set form (look for a K in the first 4 digits of the hull number).
Though similar in looks and detailing to the Westsail 32, the smaller boat is a ground up redesign by Herb David and features a number of key improvements. The rig has a taller aspect ratio, the keel is noticeably cut away in the forward sections improving her manoeuvrability, while the garboards are less hollow which help her track closer to the wind.
The resulting boat in comparison to the Westsail 32 is more manoeuvrable with a much more responsive helm and the ride is a tad drier (something the Westsail 32 suffered from). In relation to her size she is faster – expect 110 mile days, but in the wrong seaway she is known to hobbyhorse.
Some of the early boats differ from later ones as design refinements were made while they were rolling out. After the initial six or so boats, 700 pounds was added to the ballast and the total displacement went from 9,500 pounds to 13,500 pounds. With the extra weight the boat sat 4 inches lower in the water bringing the total draft to 4 feet 4 inches. Extra canvas was added to compensate, going from the original 480 sq.ft. to 545 sq.ft. The rudder was also enlarged and around hull number 20 a boomkin was added. In total only 78 boats were produced before the molds were sold in 1979 and shipped to Mexico, a far cry from the 800+ Westsail 32s in existence.
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