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)
Originally featured in one of the classic books of yacht design, the Pipedream 37 is a boat can often be found juxtaposing fine Sparkman and Stephens pedigree with the romance and trials of home-built boat projects in far flung places throughout the world. Francis S. Kinney (1915-1993) penned this unmistakably classic cruising sloop in 1960 while working in the offices of Sparkman and Stephens. She’s a well-behaved and versatile boat; her generous cockpit accommodates a large crew for daysails and coastal cruising, yet her timeless seaworthy traits make her a safe choice for offshore work.
The boat first featured in “Skene’s Elements of Yacht Design”, one of the standard texts for naval architecture. Despite being relatively well known through the book, relatively few examples of the boat were produced, the boat never made it into large scale production. Most examples of this boat are from custom builds in wood from the original design plans featured in the book. Oscar W. Schelin (1895-1980) of Kungsors Yacht Yard (Sweden), constructed the first two boats including “Southerly” in 1961 which is featured extensively in Kinney’s book. Her sistership “Avocet” was built in the following year. The boats were built in mahogany using carvel construction. Kittery Point Boat Builders (Maine, USA), under consultation with Francis S. Kinney, produced four hulls in GRP, finishing 3 of them themselves.
The Pipedream 37 has all the pleasing lines of classic sloops of its era that you’d expect; large overhangs, low freeboard, and a very sweet sheer line. It features a cutaway keel and rudder combination, though slower than modern separate fin and rudder designs, for the conservative minded cruiser it offers excellent tracking and structural integrity.
There is generous space in the cockpit, it’s fully capable of accommodating a large crew count for daysails, ten at a stretch. What is sacrificed is interior volume below deck which may be limiting for those planning extended blue water passages. In the original drawings, there are berths for six. This includes four berths in the main saloon via settee and pilot berths, and in the V-berth are two singles; bear in mind layouts will vary between boats as many boats have been customized.
Despite the age of the design, the boat is no laggard; surprising given its relatively short LWL and increased wetted area of its modified full keel and classic wine shape sections. The boat is exceptionally well balanced with finger-on-tiller tracking and a responsive helm, owners comment on her being a fun boat to sail. She has a tendency to heel early which lengthens her waterline, and once heeled she moves briskly. In light winds of 10 knots, the boat can comfortably make 4-6 knots at most points of sail depending on sea conditions. In stronger winds, given the relatively short waterline length measured by todays standards, 7.5 knots is generally the upper speed limit outside of surfing under spinnaker. Like most Sparkman and Stephen designs of its era, the ride is quite wet, and in a strong breeze the low freeboard means often the gunnels will be below the water. There is a some amount of hobby horsing in the rough, common to full keel boats of this configuration.
Few examples are available on the market and construction varies with the custom build nature of this boat. As of 2010 it’s estimated the asking price for professionally built boats range from $50k – $110k USD.
» CKD Boats, accounts and photos of two custom built Pipedream 37s in Cape Town South Africa,  
» Kittery Point Boat Builders, built 4 GRP hulls
» Skene’s Elements Of Yacht Design, the classic naval architecture book.
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