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)
After years of building small sturdy daysailers from as early as 1964, the Cape Dory 25 was Cape Dory’s first foray into fully fledged cruisers. The story goes that founder Andy Vavolotis got a hold of the molds for the Greenwich 24 from Allied Boat Company in 1972 and raised her freeboard to improve headroom, thereby adding seven inches to her length.
Other alterations included a fully enclosed head, a hanging locker, and an enlarged galley. She’s a sloop rigged full keeler with a narrow low-freeboard hull that invites a wet ride. The design is quite dated but traditionalist will love the classic lines and underwater profile, and of course true to Cape Dory tradition, the construction is bulletproof.
Though the Cape Dory 25 was designed for coastal cruising some have taken their boats offshore. Author Ed Campbell writes of cruising the Gulf Coast of the United States, including a passage to the Bahamas. In one incident his Cape Dory 25 survived a collision with an underwater cable strung between two offshore oil rigs. For offshore work, no doubt good prep is in order, the guys at Atom Voyages suggest reducing the cockpit footwell volume and modifying the companionway dropboards so they don’t fall out when raised slightly.
Headroom is only five feet down below, this didn’t get fixed until the 25D successor came along which bumped it up to five feet eleven inches. Power comes by way of an outboard situated in a well in the lazerette. There have been small changes through the years including a switch from fixed port lights to bronze opening ports around 1979.
Production ended in 1982, when the model was replaced by the beamier, heavier, and deeper Cape Dory 25D. Of all the offshore capable Cape Dorys, non have sold better than the original Cape Dory 25 with a total production run of 846 boats.
» Cape Dory Owners Association, Cape Dory 25 brochures, owner discussions, and further information.
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