Technical Information
This page gives some technical details regarding Ten Raters as well as an historical account of model yacht development.
Ten Rater Class Rules - pdf download
Ten Rater Measurements - pdf download
Technical Development of Model Racing Yachts
Summary by David Keay
The measurement of full sized boats, to assist the Tax Collector, was defined
by an Act of Parliament in 1694:
Tonnage = Length x Breadth x Depth of hold
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96
Depth proved difficult to measure so it was assumed to be ½ Breadth & the Act was revised in 1720. Sail area was of no interest.
The challenge was to build the fastest boat to beat the Revenue Cutters using 1/12 scale models as prototypes (London 12’ Experimental Class) so both developed in parallel, looking for the optimum ratio of length/beam. Boat speed (non-planing) is limited by length so under the rule length could be increased at the expense of beam. To preserve stability, draft & weight increased so the ‘plank on edge’ style evolved.
That this was dangerous was confirmed by the foundering of Patons ‘Oona’ in 1886, & unsuccessful compared with the American route, demonstrated by their winning the America Cup in 1851, & further challenges.
Ballast is necessary for stability, a keel improves windward performance. Until the early 19th C all ballast was internal when Cooper introduced a lead shoe, but this created full size structural problems (split garboards & even occasional loss of the ballast keel). New materials now permit bulb keels as normal for serious racing such as the America Cup & models.
Early models needed to be portable (small) but owners were instinctively
competitive, with sweepstake racing. MYSA defined 2 classes:
1st Class: stem to sternpost (LWL) 2’6” plus counter 3 ½”
(2’9 ½” O/A)
2nd Class: LWL 2’ plus counter 2 ½” (2’2 ½”
O/A)
Conventionally 1st Class was schooner rig & 2nd Class cutter, but cutter
rig proved superior so could be elected for races in either class.
In 1855 the Royal Thames introduced Thames Measurement for Tonnage & in 1884 Dixon Kemp (then Commodore of the Serpentine MYC & Editor of The Field) proposed a rule, adopted by the Yacht Racing Association in 1887:
Rating = Waterline Length x Sail Area
................................. 6000
This encouraged ‘skimming dishes’ which was fine for level racing
by models & small keel boats such as 5rater, 1rater, ½ rater, &c.,
not requiring accommodation.
The Linear Rule of R.E.Froude was adopted by the YRA in 1896, bringing back
beam & introducing a girth factor(G): R=(L+B+.75G+4D+1/2 sqrt(SA)/2.1,
but this still permitted ‘skimming dishes’.
The first London introduced its classes – e.g. 30 ton, & had the
12’ ‘experimental’ class, but principally the 15 rater class
to the Dixon Kemp rule. These were 43’’-44’’ W/L with
2000-1900 sq’’ sail area. The same boats were the 42 Class under
the Froude or Linear Rule.
The ‘new’ London defined 3 classes:
1st: 15 Rater
2nd: 10 ton (1/12 scale YRA Rule of 1883)
{(lwl*beam)2 * beam} / 1730
3rd: 240 class (lwl * beam < 240
Each club naturally favoured their own designs, but for inter-Club matches
classes ratified by the Ruling Authority were necessary.
European Nations formed the IRYU in 1906 & agreed modifications to encourage
fuller hulls: R = [L+2G+ sqrt(S) –F]/2.37
This resulted in the graceful metre boats: e.g.,6m,8m, & 12m.for the America’s
Cup.
In 1912 the Boat Racing Association combined the American rules, principally:
Seawanhaka (1883): R = {L + sqrt(sail area)}/2
Herreschoff Universal (1909): R = 0.18L * sqrt SA / 3sqrtD.
Resulting in: R = L*sqrt(S)/3*cubert(Dis) + L/4 + sqrt(S)/4
This was later adopted for the 18ft Class & a variant of the rule was
used for the first Fastnet Race in 1925.
The objective of a Universal Rule (full size, Worldwide) is to handicap all styles of boat so they have an equal chance of winning (the elapsed time is adjusted to corrected time according to the rating) & results decided on corrected time.
Much energy was expended over the next 60 years in amalgamating these rules,
& placating advocates of each, with guidance by Olin Stevens & Heckstall-Smith.
The result is: R = 0.13L * sqrt(S)/sqrt(B+D) plus terms allowing for stability,
propellers & other features, with definitions of L, B D, &c.
There are complex rules for measurement but this International Offshore Rule
was eventually agreed in 1970.
Model Rating followed a similar route with detailed measurements. That for
A-Class, after 5.5m promoted by Heckstall-Smith took from 1913-1927 before
ratification:
R = L * sqrt(sail area)/4 + L * sqrtA/12 * cube root(Displacement)
The first term encouraged light displacement, the second heavy displacement.
Models were around 2m O/A, 1 sq. m sail, weight 20kg.
That for 6M: R = L + 2d + sqrt(sail area) – F/237.
These were around 1m. W/L. 9’’ draught, .7 sq. m. sail, weight
12 kg.
Happily for models racing is by equally rated classes, with more pragmatic
rules for principal dimensions, which allow developments in hull shape. Thus
the 10R, Marblehead, 1m. &c.
Development of Self Steering
Boats built to the 1720 Rule had heavy weather helm, balanced by attaching
the Jib to a bowsprit, sometimes nearly as long as the hull. When models heeled
in response to an increase in wind strength, weather helm returned.
To compensate a free swinging rudder was added, ballasted with up to 1lb.
of lead, & a range of rudders could be fitted for different wind strengths,
or the rudder had a reversed tiller with a moveable weight.
The American Yacht Club (based in Central Park, New York) linked the main sheet to the tiller to assist steering in varying winds around 1890. This idea was developed successfully by George Braine, with a characteristic quadrant to attach the sheets.
The vane was originally designed by Nathaniel Herreschoff in 1875, revised by E. Metcalfe in 1905 & by Jac M. Iverson of Stockholm in 1931. It was used by Sam Berge of Norway in 1935 when becoming International A-Class Champion. It was then adopted by Marbleheads in Scotland by 1937 & eventually became almost universal.
Francis Chichester developed a full-size version from models for his single-handed transatlantic wager with Blondie Hasler, Val Howells & David Lewis in 1960.
Radio Control had been researched from the earliest days with spark transmitters, coherers, & the rest. Military applications received an impetus with the second world war but the equipment was massive. The development of the transistor & servo feedback resulted in small, reliable systems by 1960.
It is amusing to note the slow adoption of developments; with resistance by the clubs, expressed in letters to the Model Yachtsman. Indeed, for marbleheads, the vane area was included as sail area, if the vane could be locked.
References: Peter Johnson ‘Yachtsman’s Guide to Rating Rule’
ISBN: 0-245-50642.2
Model Yachtsman & Marine Models
Lonely Sea & Sky Francis Chichester