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National 10 (Turnabout) is a 9′ 8″ / 3 m monohull sailboat designed by Harold R.Turner and built by JG Marine starting in 1953.
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 √LWL
A 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)
Most recent known builder (2015):
JG Marine
67 Skilton La.
Burlington, MA USA
The NATIONAL 10 was originally known as the TURNABOUT CLASS, built in 1953 by Harold R.Turner as a small wooden single or double handed junior training dinghy. Many boats were completed by “do it yourselfers” from kits.
Fleets have been located primarily in New England and Northeastern regions of the U.S.
In 1972 the TURNABOUT CLASS formally changed it’s name to the “NATIONAL 10” class. It also decided to refine the class by approving a new mold, adhering to the original wooden design as much as possible. This was accomplished by J.R.Duplin Marine with some major improvements, including aluminum spars. The minimum class weight of 215 lbs was increased to 255 lbs. to keep both the older Parker River turnabout, the woodies, and the new Duplin National 10’s more competitive.
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