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)
Beautiful, strong, and capable the Orion 27, introduced in 1979, was one of the earlier boats to come from the well trusted Pacific Seacraft stable. Pacific Seacraft built its reputation on robust boats constructed with attention to detail. It was notable for being the last design by Henry Mohrschladt, who was one of the two original founders of Pacific Seacraft. Built in California, most examples to this day can be found on the West Coast and at least one has circumnavigated. Brec Morgan set out in Otter in 1998, visiting over 50 countries before completing his odyssey in 2003.
Unsurprisingly for a Mohrschladt design, the Orion 27 has conservative lines. Under the waterline is a long keel with a forefoot cutaway to improve nimbleness and reduce wetted area. The sections carry the tried and true wine-glass shape. Don’t expect record setting pace with this kind of shape; think strong, safe, and good manners for heaving-to in the rough. There’s a 6’1″ bowsprit to help carry her canvas and the rig came in 3 variations; sloop, yawl, and cutter. The cutter rig, best suited to longer distance sailing has a self tending staysail.
In addition to the three rig options, Pacific Seacraft offered two cabin layouts, and steering in tiller or wheel; note most examples are found with wheel steering. In 1981 an improved MkII version was introduced with a longer coachroof, two deck hatches, and an extra set of portlights.
The two layouts were named “A” and “C”. Both have a double v-berth, a hanging locker, a head, and a quarter-berth. A shower located in the head was an optional extra as was a pressurized water system for it.
The A-layout is more common and has a relatively roomy U-shaped dinette to port, lowering the dinette table converts the area into a double berth. On the starboard side is the galley with a nav-station further aft.
The C-layout was designed for longer cruises. Here the U-shaped dinette is sacrificed to gain room for a larger head and shower combo as well as providing space for a larger v-berth and more stowage in the forward sections. At the bottom of the companionway is a wet locker.
Through the years the boat has proven to be of sturdy construction. The hull is of hand-laid fiberglass and the decks are of glass cored with plywood. The hull to deck join is a double-flange bedded in polyurethane adhesive, thru-bolted with stainless bolts. This forms the bulwarks which encloses the deck and is capped in teak.
» Orion 27 Owners Yahoo Group
» A Field Guide to Sailboats of North America by Richard M. Sherwoo, p192
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