fivepointfive - April 2023

DESIGN RULES and THE A CLASS
Mighty oaks
from tiny acorns grow
In 1922 the editor of the Yachting Monthly, Maldon
Heckstall-Smith created a formula which was intended
to be used to provide a rating for all sizes of boat.
His dream that the formula would be used for small
affordable yachts was realised when the formula was
adopted to become the 5.5 Metre class rule in 1947.
The idea of the formula started with incorporating the length
and sail area rule of the lightweight rater boats, with a displacement
factor which encouraged a healthier form of hull and more sail area.
Limits were placed seriously penalising the rating if the boat was too
heavy, light, deep or had insufficient freeboard etc.
The Yachting Monthly magazine gave a magnificent Hundred
Guinea trophy to encourage model experiments/research in yacht
design, setting the ‘Yachting Monthly 6 metre rule’ at a scale of 2
inches to the foot to produce elegant looking model yachts with
a rating of 39.37 inches, which initially produced boats with a 44-
inch waterline, 37 lbs displacement and the sail area of 1850 in².
The class now known as the ‘A’ class created a lot of interest
from European countries as well as from the USA and drove the
design development to bring out the best of design, construction
and racing skills for these early international competitions. Two
boat testing by match racing provided an ideal platform for
research, which is still relevant today. Every year ever since then,
the week-long National Championship has been hotly contended
with every designer searching for better speed or handling.
1925 Bill Daniels sailing his Crusader, winner of first YM Cup (London MYC)
On its centenary, Roger Stollery looks at how the
‘A’ class developed from the same rule as the 5.5 Metre
Above: The ‘Rule’ and 1923 Admiral Turner’s Dayspring profile lines drawing
(Robert Hobbs) • Top: 2005 World Champs - Radio ‘A’ boats racing round
leeward mark (Roger Stollery)
Several milestones were passed, like the development
of the Bermudan rig, hull balance theories, the vane gear
which transformed steering downwind in 1935, thanks to the
Norwegian, Sam O Berge and development of non-porous sail
material in the late 1930s. The effect of the vane gear allowed
bigger jibs and spinnakers, so the boats got longer and heavier
to balance the effect of the more powerful rigs. The advances
continued into the 1950s when varnished terylene sail material,
an offshoot of the electrical insulation industry along with metal
masts was commonly used so that
at the end of this era waterlines
had stretched to 54 or 56 inches
and displacement increased to
similar figures.
In the 1960s the availability of
good quality terylene sail material
allowed better shaped sails to be
made, which again gave more
power to the rig and again led
to longer waterline lengths up to
60 inches and displacements to
70lb and upwards, even though
the sail areas were reducing
proportionately. One factor that
led to the end of this line of this
Yachting Monthly Cup
(Martin Bandey)
62 • fivepointfive • APRIL 2023