100 YEARS
OF THE
10 RATER RULE
RUSSELL POTTS
COPYRIGHT 1987
1
This 5th World Championship regatta for radio 10-raters marks the centenary of
the Length and Sail Area Rule, introduced by the (English) Yacht Racing
Association (YRA) on 1 January 1887. Though it had only a brief life as a full
size Rule, it was quickly adopted by model yachtsmen and has continued in use by
them ever since. It was also the vehicle for many significant advances in model
yacht design and sailing practice and its 100 year history may be used to
illustrate the way design is influenced by current theory and by available
technology.
THE ‘1730’ RULE
Before 1887, the Rule for full size craft was the Tonnage Rule of 1881 to the
‘1730’ formula:
Tonnage for rating =
(L+B)2 X B
1730
(L = Load Waterline Length; B = Extreme Beam)
At this period full size yachts of widely varying dimensions raced together and
the Rule sought to measure the ‘size’ of the hull so that the advantage of sheer
size could be eliminated by various systems of ‘Time on Distance’ handicapping.
The ‘1730’ Rule taxed beam very heavily and typically produced deep narrow hulls
with little form stability. Stability was supplied by a very heavy lead keel
carried deep. The type was known as ‘plank on edge’ or ‘lead mine’ for obvious
reasons. Sail area was unmeasured and yachts were heavily sparred and
extravagantly canvassed, requiring large crews to sail them effectively under
racing conditions. When their racing days were over, they were regarded as
acceptable cruisers under reduced rig; the hull form gave standing headroom in
relatively small boats and the narrowness of the accommodation and the
difficulties in taking the ground in tidal harbours were largely discounted.
‘
Clara’ 20 tons
midship section
2
MODELS UNDER THE ‘1730 RULE
Though the ‘1730’ Rule was in force only from 1881 to 1887, it was of great
importance in the development of model yachting in Britain. During this period
the sport was first beginning to be organised on more than a local level. One of
the main aims of Tom Bruce, the editor of the first specialist model magazine
‘Model Yachtsman’, was to promote interclub racing. This demanded the use of a
common Rule and led many model yacht clubs to builds boats that would rate as 10
Tonners under the ‘1730’ Rule when measured at a scale of 1 inch to the foot
(1:12).
In model sizes, the 10 Tonner was a boat ‘of convenient size to take on a train
to a distant town and light enough to be carried from the railway station to the
lake without undue effort’. (About 48 inches loa and total displacement of up to
20 pounds.) Model 10 Tonners resembled their full size sisters in general form
but were in many cases more extreme in their proportions with a length of five or
six beams and even more outrageous sail plans. They used a series of rigs of
various sizes to suit weather conditions. The boats had a long straight of keel
and were sailed to windward without rudder, using sail trim alone. Off the wind,
if they raced off wind at all, they were steered by the use of a free-swinging
weighted rudder. A range of different sizes and weights was used to suit the
course and wind strength. Many clubs felt that the problem of off wind control
was too difficult; others maintained that an intelligent use of a suite of
weighted rudders would give all the control that could be desired. Much depended
on local traditions and conditions.
At this period, the model yachtsman could make no mid course adjustments to helm
or sail trim to meet changes in wind strength and direction. Thus, straight
running and the absence of steering tendencies were of paramount importance.
There was, however, no theory to support his design efforts to achieve this end.
Hull ‘balance’ was recognised as desirable, and most naval architects emphasised
the importance of ‘harmony between the entry and delivery of the hull; none gave
any indication of how this could be assured at the design stage, other than by
intuition and long experience. Well into the 20th century, many successful full
size yachts were notoriously hard mouthed and difficult to control in a blow,
with the long narrow straight keeled boats to the ‘1730’ Rule, this did not
create too much difficulty.
3
Fig 3
a model 10T
THE LENGTH AND SAIL AREA RULE
In 1887, in an attempt to produce a less stereotyped form of hull, the YRA
introduced the Length and Sail Area Rule. This was devised by Dixon Kemp, who
was both Secretary of the YRA and Yachting Editor of the sporting weekly ‘The
Field’. This rule for the first time took account of the propulsive power of the
sail area as well as of the size of the hull. The formula was:
L X SA
6000
(L = Load Waterline Length; SA = Sail Area, measuring the whole area of all sails
of the largest rig.)
The rule for the first time required a limited sail area to be used to the
maximum efficiency, and the hull resistance to be reduced by more efficient
design. The effect was for the hull to become lighter, shallower and broader,
with much of the stability coming from the hull form. Simultaneously, the hull
profile began to be cut away, as the findings of William Froude on the
importance of skin friction came to be generally accepted. As the hull depth and
displacement were reduced, fins became narrower and deeper, with smaller amounts
of lead carried at relatively greater depths.
Rating =
4
These trends were carried furthest and fastest in the ‘Small Rater’ classes of
level rated dayboat that sailed in the Solent. The 0.5 and 1 rater classes in
particular were the arena for fierce competition in design and construction.
These small keelboat and centreboard classes, in which Soper, Sibbick, Payne and
Linton Hope were the leading designers, saw the development of the ‘skimming
dish’ hull with great beam, long overhangs, a fin and bulb keel, and a skeg
mounted or spade rudder. Great emphasis was placed on minimum structure weights.
The type also produced the ‘Solent rig’, which maximised the efficiency of the
limited sail area by concentrating it in a high peaked gaff mainsail, often with
through battens, and a small jib.
Fig 4 ‘Unora’, 1894;
Solent Small Rater
THE COLLAPSE OF THE LSA RULE
Despite the success of the Rule in fostering an exciting, if expensive,
group of small dayboat racers, it was not popular with those who wanted a
rather large boat. The Victorian yachtsman expected a high standard of
accommodation in boats large enough to live aboard and the lsa Rule with
its shallow hull form did not permit standing headroom until the yachts
reached quite large sizes. This meant that a racing yacht which had become
outclassed could not be used for the style of cruising that owners of the
time preferred and thus had little or no resale value. As early as 1892
the falling off of new orders for yachts of over 10 rating was causing
concern to yacht designers and builders, who feared for their livelihoods.
A committee, led by Fife and Watson, waited upon the YRA to urge that a new
Rule be introduced which would require hull forms that would give adequate
accommodation and preserve the link between racing and cruising yachts. It
was also argued that the more extreme styles of boat under the Rule were
unseaworthy. This is an objection that tends to be raised against any Rule
by those who, for whatever reason, wish it to be changed.
The YRA declined to take action, on the grounds that ‘their members desired speed
above all’. It was also known that 1893 would see the launch of a large (142rater) yacht to the Rule for Edward, Prince of Wales, and the YRA did not wish to
snub this move to give a Royal cachet to yacht racing. Watson’s design for the
Prince, the famous ‘Britannia’, had some success in her first few seasons and
prompted a few other wealthy owners to build large yachts to the Rule, but this
did not make the Rule acceptable to owners of smaller yachts. In 1896 the YRA
agreed to adopt a Linear Rating Rule devised by J. E. Froude. This was intended
to bring racing and cruising yachts together in a common form and used a system
designed to ensure that even out-and-out racing craft would have a hull form that
would provide a practical cruiser with ample accommodation. This Rule came into
use in January 1897 and set the broad pattern that was followed in the various
revisions of the Linear Rating Rule and in the International Rule introduced by a
conference of European Yachting Associations in 1907 and revised several times
subsequently.
5
Though the Linear and International Rules were adopted by model yachtsmen, they
never supplanted the popularity of the 10-rater, which continued to be by far the
most popular class in Britain until well after 1945. From the turn of the
century until the late 1960’s there was an active and highly competitive 10-rater
League in the London area. Many important design innovations were developed
within the context of 10-rater competition.
EARLY MODELS UNDER THE LSA RULE
Model yachtsmen did not immediately adopt the new lsa Rule in 1886. They were in
general keen to build to the current full size Rule, but the 10 Tonner already
existed as a common interclub boat and was not easily displaced. There was also
uncertainty over which was the best size to adopt for a model under the lsa Rule
and initially the 15-rater was favoured. The ‘Model Yachtsman’ ran a design
competition for 15 raters in 1891 and these are the earliest surviving model
designs to the Rule. The designs mimic the style of larger full size yachts
under the Rule, with a full keel and wine glass hull form; the rig is usually a
cutter. Similar competitions for 10-rater designs were held in 1893 and 1894.
By this time some of the entries are looking to the style of the Solent ‘small
rater’, with a shallower canoe body with fin keel. The competition entries range
from 38 to 40 inches lwl and from 19 to 25 pounds displacement. Sail area was in
the region of 1500 square inches.
Fig 6
‘Blackbird’
10-r,
6
Greenock
1895
DESIGNING COMPETITION
FOR 10-RATERS.
Fig 5,
1894 Competition entries;
The main design problem faced at this stage was to produce a hull which combined
the speed advantages of reduced wetted area with the tractable steering
characteristics essential in a successful model. The specialist magazines of the
period make it clear that the most advanced modellers had not found a solution.
The competition entries of 1894 include an early example of one ‘solution’. This
is the twin fin; twin fin boats, and even triple fin configurations, had a wide
vogue in the period 1893-1910. The style was regarded as the best (or least bad)
solution to the model yachtsman’s problem. It was, however, a solution of brute
force rather than design. It was not ideal, as the wetted area that had been
saved in the hull was returned in the excessive fin area and there were also
problems with the turbulence generated by the multiple appendages. A twin fin
configuration was experimented with in the full size Small Rater ‘Corolla’ in
1894, but was found to be much slower than the conventional fin of the period.
Modellers, however, could only persevere with the twin fins and renew their
experiments with automatic steering devices to control the boat on off wind legs.
7
Fig 7
Fig 8,
‘Zebra’.
‘Shamrock’,
8
1900
1899
STEERING DEVICES
Many styles of automatic control had been tried at earlier periods, but none had
won favour. As Tyrell E. Biddle wrote in 1894 ‘They spring up every season, like
the flowers in the spring and fade and die like autumn leaves. The weighted
rudder continues for ever.’ However, the early years of the 10-rater Rule saw
automatic systems come into general use.
A wide range of types was used, from a simple reverse tiller operated by the
mainsheet to the most fearsome and complex collections of engineered brasswork.
The most popular was that devised by George Braine of the Model Yacht Sailing
Association at South Kensington and first used in 1904 on his twin finned 10rater ‘Buttercup’. This gear gave a greater range and greater subtlety of
adjustment than its competitors and was within the constructional capacity of
most modellers. With a few minor improvements over the years, this gear
continued as standard equipment for racing models for 40 years until it was
replaced by Vane gears of various types.
Fig 9,
Braine Gear
DANIELS AND VOLUMETRIC HULL BALANCE
The introduction of effective steering gears helped on the off wind legs, but
boats were still sailed to windward with the rudder locked and had to rely on
hull balance and the fine tuning of sail trim to make their most effective
course. The breakthrough in design practice and theory came in 1905-6, when Bill
Daniels, then a young man in his early twenties, produced the 10-rater ‘XPDNC’,
with which he won the Highgate Bowl and other important trophies in the London
area. In an article written in 1915 he explained that his aim was to produce a
9
shallow hull with a fin and bulb keel similar to the Solent Small Raters, and to
solve the problem of hull balance, so that the boat would have no steering
tendency as the angle of heel changed. He claimed that the prototype of the boat
was sailed with five different fin configurations and fifteen different rigs
before he recognised that the solution had to be in the design of the hull
itself. He developed a method of determining hull balance by calculation of
upright and heeled centres of buoyancy at the design stage. The hull form was
then adjusted until the fore and aft movement of the CB was reduced to a minimum,
typically less than half of one percent of the lwl. I have been unable to find
any earlier comparable design procedure in the full size literature. Though a
purely static balance, this method produced a vice free boat in practice.
Most generations of model yachtsmen claim in their writings that, while their
predecessors were engaged in games for boys, they had reached the level of a
scientific sport for men. Daniels made such a claim in 1913 at the banquet held
after a British team had comprehensively defeated French and Belgian model
yachtsmen at Enghien-les-Bains in the first formally organised international
model yacht competition. Unlike some others who have made the claim, he was
right. His design techniques, coupled with the use of the Braine gear, set the
pattern for the technical development of the sport for the next 60 years.
The success of his boats ‘XPDNC’ and the later ‘Onward’ of 1911 and their copies
and close cousins resulted in the near standardisation of 10-rater design, at
least in London and the south of England, from their introduction until the late
1920’s. These design concepts also had great influence elsewhere in Britain and
the Empire through their publication in the journal ‘Model Engineer’, and in the
1913 and subsequent printings of the Percival Marshall handbook ‘Model Sailing
Yachts’. In this form the design ‘XPDNC’ remained in print until 1951. Boats
influenced by Daniels’ designs were being built in New Zealand by 1915.
The typical 10-rater of the period was about 60 inches overall, 36 to 38 inches
waterline and up to 1600 square inches of cotton sailcloth in a Solent rig.
Displacements were in the 15 to 17 pound range. Braine gear was almost
universal.
Fig 10,
‘XPDNC’,
10
1906
Fig 11, ‘Oriane’,
Fig 12,
before 1914
10-r on the Round Pond,
before 1914
AERODYNAMIC THEORY
So universal was the Daniels influence, that in 1923 Edward Hobbs wrote that the
class was played out in its design development; he did not anticipate any
further significant change in the style of boat. In fact, as he wrote, things
were changing. On the one hand, the MYA adopted the YRA (full size) method of
measuring sail area, which had the effect of substituting batten limits for cloth
measurement as a means for controlling the roach area of sails and also
substituted an ‘85% of fore triangle’ measurement. These changes potentially
gave additional free area, particularly if the leach lengths of sails could be
increased.
11
So long as gaff rigs continued in use the effect was relatively small, but
aerodynamic theories developed in 1912-13 for aircraft wing design by the French
engineer Eiffel and by a British team at the National Physical Laboratory began
to reach yachtsmen in the early 1920’s. The work of the American Manfred Curry,
originally published in Germany in 1925, incorporated the results of the first
wind tunnel work aimed at sail rather than wing design. Alfred Turner, the
greatest theoretician of model yacht design of his day, quickly picked these
ideas and in 1926 proposed Bermuda rigs of much higher aspect ratio than either
the gaff rigs then used on 10-raters or the Bermuda rigs found on the A Class and
6-metre models of the period. He argued, as did H. B. Tucker, the Chairman of
the MYA and editor of ‘The Model Yachtsman’, that such a rig would make more
efficient use of the sail area and would maximise the benefit of the free roach
area given by the change of the Rule. Thus a smaller measured area could be used
to generate, within the Rule, a longer hull which could still be efficiently
driven.
The height of the sail plan required a more efficient rig with a hollow mast,
either in wood (only practicable with the advent at this period of reasonably
water resistant glues) or metal tube, and improved staying systems deriving from
full size practice and making use of wire and rigging screws rather than cord and
bowsies, as had been the norm earlier. Even so, increased rig height and
efficiency called for greater displacement and more ballast to extract the
available power from the sails. Tucker spoke of 50 inches lwl as a practical
aim, but the first boat of the new generation made a comparatively modest step in
this direction, with a lwl of only 43 inches and a sail area of 1395 square
inches. This was Jim Steinberger’s ‘Phoenix’ of 1930. The most impressive step
forward is in the very tall sail plan. She was phenomenally successful in her
first season in a very competitive 10-rater fleet in London and had great
influence, as did her successors, ‘Ballerina’ and ‘Coquette’.
Fig 14,
‘Phoenix’,
1930;
In 1934 the first 50 inch lwl boat, ‘Vivix’, was built to a Tucker design and
very gradually a 48 to 50 inch, 25 to 27 pound boat became the norm for new
designs and sail plans standardised on a Bermuda rig of high an aspect ratio; few
boats however carried rigs as tall as ‘Phoenix’, which had a 77 inch hoist. Many
existing 10-rater hulls were converted to Bermuda rig and given additional
ballast to compensate for the greater sail power. ‘Angus’, which is present at
this regatta is an example of this style of boat. She was built some time in the
late 1920’s and converted, relatively late, in 1945.
12
Fig 14, ‘Ballerina’,
1934
The downwind power of the smaller rig was improved by the use of a kicking strap,
which was widespread in models long before it was adopted by full size sailors.
There were also improvements in the spinnakers used, both in design, with the use
of balloon spinnakers set outside the jib, and in material, with the use of jap
silk for lightweather ghosters. This line of development continued when sailing
resumed after the 1939 war and British skippers started to come to terms with the
use of the Vane gear.
SAIL TECHNOLOGY
The next important change was a significant advance in the efficiency of the sail
material. In 1952, model yachtsmen discovered varnished terylene, used in the
electrical industry to insulate transformers, and adopted it in place of cotton
for their sails. This change had been anticipated to some extent by the ‘XL’
sailcloth produced in the late thirties by H. G. Perks. This was a cotton
treated with a ‘secret formula’, but was not widely used and in any case was not
produced after 1939. Various other attempts to improve the performance of cotton
by painting it with dope or varnish were made, but none were entirely successful
and it was only the universal adoption of varnished terylene ‘tin sails’ in the
early 1950’s that had an effect on design. Sails made of the new material were
about 15% more efficient than cotton and allowed larger unmeasured roaches to be
effectively carried. The effect was of course to reduce measured sail area
further and push lwl up to 55 and eventually 60 inches.
At the same time as synthetic sail material was coming into use, the first
faltering steps were being take in the use of glass reinforced plastics for hull
construction. Wooden construction remained the norm for several years and even
those boats built in GRP did not fully exploit the potential savings in structure
weight. There was little need to do so because, under the influence of the
increasing efficiency of the rig, the trend in the class was for boats to get
slightly longer but a great deal heavier. The extreme of this development was
reached in John Lewis’s ‘High Tension’ of 1964. The waterline was 60 inches,
giving only 1000 square inches of measured sail area. The displacement was 34.8
pounds and the ballast was contained in a thick, laminar flow, fin composed
entirely of lead.
13
Fig 15, ‘High Tension’,
1964
SAIL PLANS
The contemporary spread of the vane gear, which had been developed by model
yachtsmen in the USA during the 1939-45 period and was almost universal in
Britain by the mid 1950’s, permitted a change in sail plans and the use of a
larger jib to drive the boat rather than a minimal jib, used largely as a
steering sail, which was typical of Braine gear practice. Similarly, the vane
gear, by separating the steering function completely from the sails, enabled
bigger and more efficient spinnakers, by now made in rip stop nylon, to be
carried down wind. This again reduced the sail area required to be contained in
the main sail plan and led to longer boats.
THE BULB REDISCOVERED
The search for increased hull power without massive displacement prompted the
revival of the fin and bulb keel, which had largely dropped from sight in both
model and full size design under the influence of the International and other
Rules which discouraged it. A very early venture in this direction was made in
1952 with ‘Triplane’, a design closely based on Uffa Fox’s ‘Flying Fifteen’
keelboat, but this was not fully followed up for some years. The fin and bulb
keel in its modern form was first used in 1961 by Stan Witty, and was generally
adopted by other designers by 1964.
In terms of the design process, this change to a large extent separated the
functions of the canoe body, the fin and bulb and permitting them to be very
freely manipulated in relation to each other, and simplified the task of
producing a fully integrated design. In the particular context of the 10-rater
Class, the bulb keel gave much greater power to hold up the rig while permitting
a reduction of total displacement to give a finer and more easily driven hull.
The desire to plane called for a serious attempt to reduce both total
displacement and the structure weight.
14
Fig 16, ‘Windwing’, Stan Witty,
1967
RULE CHANGES
The development of sail plans and sail materials had given a great increase in
the effectiveness of the rig which had encouraged the longer lighter planing
hull. In 1966, Roger Stollery’s ‘Warlord’ design exploited this trend fully. It
also redesigned the hull construction to suit the available GRP technology and
used, for the first time, a wing mast, which gave substantial free area under the
Rule as it then stood. The boat would sail effectively to windward under the
mast alone and outclassed the existing designs. Following her success in the
1966 MYA Championship, the Rule was revised with effect from 1969 so that the
whole of the sail cloth was measured, as was the area of the mast. This
increased the measured sail area of all existing boats and to keep existing boats
within rating, the divisor in the Rule formula was amended to 7500. Changes in
the way spinnakers were measured tended to encourage smaller main rigs and larger
spinnakers.
After the Rule changes, the trend to lighter, longer boats continued, with
waterlines rising of 64 and 65 inches, which had been rare, became commonplace.
(‘Cracker’, John Lewis 1972). At this stage the class began to go into a decline
in Britain, partly because of the general decline of vane sailing and the
overwhelming popularity of the Marblehead in the radio fleet, partly because the
downwind speed of the boats made sailing them under vane a pastime for the young
and very fit. John Lewis continued to design boats for the class, but the number
being sailed fell away.
15
DESIGN FOR RADIO SAILING
Radio 10-rater sailing was originally no more than putting a radio into existing
vane designs, and initially ‘Cracker’ was a favourite vehicle for radio in
Britain. It soon became evident that however efficient this ‘toothpick and
pocket handkerchief’ type of design was to windward under vane, as a radio boat
it had disadvantages. The accuracy of trim required to make effective use to
windward of the small high aspect sail plan was not possible to obtain under
radio; even more important, the loss of the spinnaker on the off wind legs of the
radio course was an insuperable disadvantage. The trend in radio boats was to
get shorter on the waterline again and to carry more significant areas of sail.
Planing performance was demanded and development followed a parallel path to that
in the radio Marblehead class, with displacements further reduced, deeper fins
and higher ballast ratios. The main emphasis has been on applying the new
technology of lightweight construction, carbon fibre masts and mylar sails to the
class. There are still wide variations in approach to the design of radio 10raters, with the concepts reflecting local conditions for which particular boats
are intended.
The internationalisation of model yachting which has followed the introduction of
radio control has meant that design inputs from France, Sweden and Australia,
among other centres have become significant for the first time in the history of
its development.
[This paper will eventually be incorporated
yachting in Britain on which the author has
cover both the technical and social history
attention to the inter-relationship between
Illustration credits:
into a comprehensive history of model
been working for some years. It will
of the sport and will pay special
model and full size developments.]
MAP Plans service/ASP: Figs 7, 9, 10, 16
Ray Brigden: Fig 11
Author’s Collection: remainder
Copyright
16
1987 Russell Potts