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 Jeanneau Gin Fizz is saltier than its name might suggest. Peddled by the fledgling Jeanneau company in the late 1970’s she’s a 37ft 6inch fibreglass production cruiser, designed by Michel Joubert, that has earned a credible reputation as an affordable offshore passage maker. Although not a classic blue water cruiser, the Gin Fizz has proved her mettle on a number of circumnavigations and plentiful ocean crossings.
Marketed in a half-hearted way in the US market as a performance cruiser, her 6′ 2″ draft may have limited her appeal across the pond but over 500 boats were produced in France between 1975 and 1980. In recent years there’s been a revival of her popularity on the used boat market. Notably she was selected by Laura Dekker for her well publicised round-the-world voyage, setting off at age fourteen in August 2010 and successfully completing in January 2012 at age sixteen (beating Jessica Watson’s record set one year earlier in an S&S 34).
Looking at her sections, the word beamy comes to mind. Most of her beam (12′ 6″ at maximum) is carried quite far forward and aft making for a roomy boat. From side on however she carries a sleek profile with a low freeboard and almost flush deck. (Despite this 6 feet of headroom can still be found inside.) A look below the waterline reveals a fin keel and partial spade rudder, a configuration considered quite modern at the time.
The early models were generally ketch rigged, such as Laura Dekkers Guppy but switched to sloop later in production. There seems to be little advantage to the ketch rig despite slightly greater sail area. John Kretschmer, writing for Sailing Magazine, maintains that the sloop version is more practical, more manouverable, and with less clutter in the cockpit.
Both aft and centre-cockpit models were offered. The center-cockpit’s aft cabin isn’t exactly palatial and could be described as an oversized storage locker but it makes for a good seagoing berth, and is in easy reach of the cockpit wheel. And course the extra privacy cannot be discounted.
Owners report that she feels solid under sail and that although she pounds in a seaway she is rugged enough to take it. She is well balanced, points high and can average 5 knots and 120 mile days in spite of her 32ft waterline.
Despite the modern configuration of the Gin Fizz, traditional heavy fibreglass construction was employed and her displacement is a moderate 15,432 lbs. Iron is used for the ballast and is bolted on externally before glassing over. Her deck is balsa cored fibreglass and the mast is deck stepped.
Her interior has been described as unremarkable with average quality joiner work. Ketstchmer lists a number of construction details that tend not to age well including tabbed bulkheads, fabric headliners, and a cabin sole that’s glass over wood and carpeted.
There is a small galley to starboard with two tiny sinks and a good sized nav table to port behind a c-shaped dinette. Up front there is a v-berth with head and hanging locker. Lighting is provided via the narrow perspex portlight which runs the length of the cabin top and it can be quite dark below. Two hatches provide average ventilation.
Issues that have been identified with the Gin Fizz include rusting of the original salt-water cooled engine, delamination of the bulkhead, and swelling of the nylon rudder bearings if the boat is out of the water for a long time. John Kretschmer advises getting the glassed-over keel bolts inspected or x-rayed.
There are generally a selection of Jeanneau Gin Fizz for sale at any given time, generally around Europe but occasionally further afield. Current asking prices are between 23,000 and 50,000 Euros.
» Jeanneau Gin Fizz, an in depth review by John Kretschmer, Sailing Magazine, Nov 2008
» Gin Fizz on Jeanneau’s official website
» Laura Dekker’s website
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