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“In
search of Speed and Weatherly Performance”
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Square Rig
The
ideal rig for sail training should include square sails
on at least one mast, particularly if operating world-wide on the Trade
Routes
when the trainees have time to become conversant with its complexities.
The
exciting downwind performance is normally offset by an inability to go
to
windward effectively. This can frustrate plans to reach upwind
locations and,
in the worst case, increases the risk of becoming embayed.
A modern solution is to ‘motor-sail’ using the
engine, making excessive noise,
wasting fuel, and creating an uncomfortable motion, which puts
unnatural stress
on the rig. Not a good solution.
Fore and Aft Rig
The
desired weatherly performance can, of course, be
achieved with Fore and Aft rigs, which are not so crew intensive, but
can
become very threatening downwind, in severe conditions. Historically, a
compromise has been struck in the Topsail Schooner, but it remains only
a
partial solution to the dilemma.
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The Polacre /
Xebec Rig
Philip
Goode, yacht and sail designer, based in Majorca as the Lloyds agent,
had a particular interest in the Barbary coast Xebec, the most
successful corsair of the Mediterranean for two centuries and,
arguably, the fastest displacement sailing vessel of all time for its
size.
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This hybrid sail
arrangement of the 'square' Norse sails on the main mast and a massive
'triangular' Lateen on the fore in one ship had spawned a cult of swift
and weatherly pirate ships whose ability to outrun their pursuers was
legendary.
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Using the
geometry of the Xebec rig, Philip had designed a
number of sail plans for modern yachts which he tested on scale models
but, in
spite of achieving exceptional results on all points of sailing, they
did not
appeal to the owners of today's maxi-yachts.
Fortuitously he was put in touch with
Graham Neilson and a collaborative
project was launched for the PELICAN.
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The
Model PELICANINA
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As a test
vehicle, Philip Goode built a 12½:1 scale model of PELICAN,
incorporating the new long poop and his 3-masted, 12-sail rig. Her centre of gravity (CG)
and meta centre (GM) had to be scaled to that of the future ship and
she had to run on her predicted draught marks. PELICANINA was
3½ metres long and weighed nearly ¼ of a tonne.
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| Test Results |
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PELICANINA
was sailed in the open sea off Palma. The results, recorded on video,
were extra-ordinary and spectacular. She proved to be perfectly
balanced, sailing fast to windward in scale winds up to 60 knots -
unheard of in a square-rigger. Her speed off the wind was exceptional
and downwind there was no tendency to yaw. It seemed that the secrets
of her Arab forebears were being slowly revealed.
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Visit www.weatherlysquareriggers.com
for more detail.
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Problems
Identified
As
expected, the Model identified several technical problems to be solved
before this performance could be replicated at full scale:
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a) Single pole masts
were required. (a la 'polacre'). The
tallest to be 100ft.
b) The yards had to brace within 18 degrees of centreline (normally 35
degrees for conventional square riggers).
c)
To avoid distorting
the square sails at these extreme angles, the pivot point of each had
to be in perfect alignment ( not possible in conventionally stepped
masts).
d) Suspension points
of yards and some stays had to be altered.
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Verification
of the Rig by Lloyds of London
Because the
unconventional sail distribution and rigging plan were bound to
raise questions of strength and security, it was decided to submit all
elements
to scrutiny under the 'Verification of Rig' procedure now available at
Lloyds
Register, in London.
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Computer
Generated Analysis
Here, all
sections of the masts, bowsprit and standing rigging were 'modelled'
and subjected to the maximum wind speeds acceptable for Full and Plain
sail, ultimately reducing to 'bare poles' in hurricane conditions at
122 knots!
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From the
predicted sail loading and ship movement the mast scantlings were
analysed for
axial force (vertical thrust), bending and buckling. Rig tensions were
then
calculated and the standard Safety Factor of 3.5:1 applied to ensure
that the
chosen wire rigging and terminals would be sufficiently robust. A
16-page
report and annexes, with colour computer graphics concludes: "the
minimum
acceptance criteria were satisfied in all cases".
The Masts
The
masts
are 20 sided steel in hollow section.
They are fully galvanised. Historically, 'lower' masts
were always stepped on
the keel, emerging at the weather deck through mast collars, with
wedges,
packing and aprons to prevent leaking. Now, stump masts, which are
integral
with the hull and deck structures are Lloyds preferred option, and are
fitted
in PELICAN. These terminate in a flange, ½ metre above the
wooden deck. The
mast itself, with an identical flange at its base, is then bolted to
the stump
ensuring continuity and water tightness.
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