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 Ingrid 38 from the pen of William Atkin is a heavy displacement blue water ketch derived from Colin Archer’s famous double ender designs, which in turn were inspired by Viking boats renowned for their heavy weather characteristics. Perhaps Atkin sums it up by saying it’s “the kind of boat that behaves herself in rough water and can be depended upon to sail herself”. (To that part we do hear frequent mentions of the superb one-finger-on-tiller tracking and a comfortable ride.)
With her old world style she’s a good looking boat with a sheer line reminiscent of the Crealock’s famous Westsail 32. Her seaworthiness is there to see in her full keel, heavy displacement and overbuilt construction. Her hull is heavily hand laid in fiberglass, there’s robust outboard chainplates and an outboard rudder protected by extra fiberglass and a large bronze shoe casting should she scrub the bottom.
Atkin’s main rework on the Ingrid 38 from Archer’s original design was a finer entry on the bow which ‘cushions’ her landing off the waves. Below the waterline she has a long full keel with deep v-sections forward keeping her stable in the rough. The ballast is encapsulated and is distributed from bow to stern, this helps her to avoid the pitching motion familiar to fin-keel sailors. Rounding this off, there’s plenty of flotation fore and aft which helps keep her dry.
The tradeoff heavy displacement and ultimate stability is usually in speed, the Ingrid 38 is not considered fast. Surprisingly she’s known to sail pretty well in light airs, owners reporting she’ll do half the wind speed up to 8 knots of wind. However, she’s a boat that comes into her own in heavier seas. By the numbers, her hull speed works out at 7.2 knots but she’ll more often manage a consistent 6 knots while cruising. The ketch rig gives plenty of options on all points of sail and she’s an easy boat to single-hand.
Around 1934 American naval architect William Atkin was bombarded with demands for a larger ketch-rigged version of the Thistle 31, a double-ender which he had recently released plans for. Atkin took the lines of Archer’s design and drew the plans for the Ingrid 38.
The first Ingrid 38s were privately built from wood, steel and cement from the plans, but it wasn’t until 1971 that production began in fiberglass by Blue Water Boats Inc (ironically located in a town called Woodinville in WA). The plug and mold for the first Ingrid was built by two Seattle sailors James Musser and Donald J. Pitblado working together, as the story goes, in a commercial chicken coop. James Musser’s original plan was to build Ingrid hull#1 and embark on a Pacific Ocean cruise but others were so impressed by his Ingrid Sandaldust that they requested similar hulls from the mold. From this demand Blue Water Boats Inc. was born. His co-worker Donald J. Pitblado went on to become the owner of Ingrid hull #2 Donna Marie
In 1973 the company took on Jerry Husted, an experienced Puget Sound sailor, as an equal partner which allowed Musser and his wife to sailed off in Sandaldust to live their Pacific dream. By 1974 Husted bought the balance of the shares and production of the Ingrid continued until about 1985 when the molds and patterns were sold off and were stored for a long time in Graham, WA. Around 1997-98 the molds were purchased by Bill Ingerson and he shifted them back to Woodinville in 2000 . Ingerson tried to get a few commitments for hulls but never got much interest at todays production costs.
The Ingrid 38 was produced at the rate of one a month for 10-12 years and there are thought to be around 143 of these boats in existence as well as those constructed from other materials. Many boats were bought as hull and deck kit sets from Blue Water Boats and finished by their owners to a variety of standards and configurations (including using cutter rigs).
A variation on the Ingrid 38 exists in the form the Alajuela 38, her hull being a close derivative of the Ingrid, built to a very high standard and configured with a cutter rig.
The Ingrid 38 is no longer in production but there are usually several available on the used boat market, mainly in the US. Current asking prices are around $35k – $79k USD. Prospective owners are recommended to contact the Ingrid 38 owners group on yahoo.com for advice or information (link below).
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