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by Duncan Cameron
The Westwind 24 was one of the very early Ted Hood performance cruising designs (1966), and may have been the first one built in fiberglass. This design certainly benefited from Hood's sailmaking prowess, and his first big racing successes. These included the original " 40' Robin " in 1959, and continued with the 1962 and 1964 America's Cup contender, "Neferti".
This background certainly contributed to the Westwind 24's efficient sail plan and surprising turn of speed!
Hood's basic concept of the Delta Form ("Whale Belly") continued to evolve through numerous designs, including seven separate models of Bristol Yachts (31'-45'),
the Hinckley 43, and the Wauquiez Hood 38. It probably reached its mature form in his own line of Little Harbour Yachts. Ted Hood eventually produced over 1600 yacht designs.
There is a "Designer Profile" of Ted Hood available here.
The principles of Hood's design philosophy are set out in "A History and Technical Overview of the Hood Design Philosophy", by the Ted Hood Design Group. (Many thanks to his colleagues, at The Fontaine Design Group, who kindly provided this excellent brochure, as well as copies of original design drawings for the Westwind).
Design Overview
(Any errors in interpretation are, of course, my own. This is simply intended as a summary.)
One of the chief benefits of Hood's designs is eliminating the high drag caused by a thick fin keel. This enables a major reduction of wetted surface, and substitutes the more efficient centreboard foil.
A number of tradeoffs must be made, of course. First of these is weight - more ballast is required. The increased weight is needed to balance the reduced leverage ("righting arm") because the ballast is carried up in the hull, instead of down below in the fin keel. Secondly, to reduce the extra ballast needed, the hull form must also be deeper, to carry the internal ballast as low as possible.
Figure 1. Hull Form and Centre of Gravity Figure 2. Centre of Buoyancy and The Righting Arm
(Ted Hood Design Group,
"A History and Technical Overview of the Hood Design Philosophy", p.7) (ibid., p.7)
.. .
As illustrated, the Delta Form hull is deeper. In this example, it also carries almost twice as much ballast, to produce the same "ballast moment" (15,000 lbs X 2 ft = 8,000 lb X 3.75 ft), compared to the fin keel.
The third major difference from a conventional fin keel design is also shown above (Figure 2), where the beam is greater. This contributes to 'form stability', i.e. as the boat heels, the centre of buoyancy moves further outboard. This lengthens the righting arm, increasing the righting moment, or 'stiffness', compared to the narrower fin-keeled hull.
Finally (well, not really, but this is just a summary), comes the fourth major difference, reduced wetted surface due to hull shape. The Hood design has deep, rounded 'V' sections, as shown below. These sections, "A", form a shorter line from the waterline to the bottom of the hull ("chain girth"), than the flatter sections + keel shown as "B". The rounder the underbody, the less drag-causing wetted surface. This reduced drag, of course, increases speed, right up to the point where the limit of maximum hull speed is reached.
Figure 3. Chain Girth and Wetted Surface
(ibid, p.9)
Conclusion:
The overall effect is to produce a large, fast boat, easily driven in moderate breezes, with excellent stability and seaworthiness. The weight penalizes acceleration, but gives her the ability to carry a generous sail plan, to carry full cruising provisions, and to maintain speed and stability in a wide range of conditions.
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