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 Allegra 24 is commonly known as a beefed up version of the Flicka 20, perhaps the most famous pocket cruiser of all time. Looking deeper there’s more to the family connection than meets the eye, co-designer of the Allegra 24, Fred Bingham, is also father of Bruce Bingham who designed Flicka.
Her designers Fred Bingham and Lou Nagy, a naval architect and civil engineer, started with the same basic hull form of the Flicka 20 and stretching her four feet without increasing the beam. The extra room is quite noticeable below deck, with a separate head compartment and nicely sized berths that are 6′ 5″ long at a minimum. Apart from this, at first glance the Allegra 24 seems quite similar to the Flicka, there’s the full keel, transom hung rudder, bow sprit and small cutter rig. Most delightful of all is the traditional charm that’s still there.
Looking deeper, there have been significant improvements in the hull form. The bow has a finer entry with more flare, there’s higher freeboard, the beam has been carried further aft and importantly, the buttock sections have been kicked up which resolves Flicka’s issue with low cockpit drains. Under the waterline the very full keel on the Flicka gives way to a forefoot cutaway and the hull further aft has a flatter run which helps her speed and acceleration.
The fiberglass hull uses biaxial glass reinforcing that’s pre-impregnated with acrylic-epoxy resin. This is a relatively modern technique that results in more glass and less resin in the layup leading to more rigidity and strength. The use of acrylic-epoxy resin should make for a very osmosis-proof hull. Decks and cabin tops are PVC foam cored and the super structure in general is of very sound construction exceeding Lloyds specification for offshore boats. It’s interesting to note there are no through-hulls placed below the waterline and cockpit drains have been beefed up to two inches diameter.
Under sail the Allegra 24 leaves all comparisons to the Flicka 20 behind. She’s a fast boat, one of the fastest pocket cruisers in her class capable of exceeding hull speed quite easily and is a particularly strong performer in light winds. Next to the Flicka, she points higher, is nimble through the tacks, and is much better slicing through chop. Her bow flare and higher freeboard makes for a much drier ride and in following seas where the Flicka tends to squat in need of more stern buoyancy, the Allegra lifts well. A quick glance at her numbers reveal three feet more waterline length, 50% more sail area, despite a displacement that’s in the same ballpark as the Flicka.
The Allegra 24 was made available in kit form or as bare hulls. Bingham organized various builders who could complete the boats on a custom basis. They were located in various locations throughout the country including Ventura CA, Riviera Beach FL, Noank CT, and perhaps others as well. The partnership between Nagy and Bingham eventually ended and the number of boats in known existence remains sketchy.
» Good Old Boat Magazine, Nov/Dec 2006 Allegra 24 by Karen Larson
» Good Old Boat Magazine, Nov/Dec 2006 Four small bluewater cruisers: A comparison of Allegra and three rivals by Ted Brewer
» The Sailor’s Book of Small Cruising Sailboats by Steve Henkel, p267
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