fivepointfive - April 2023

DESIGN
The 123 of
5.5 Metre design
Steve Quigley and Kate Devereux from One2three Naval
Architects in Sydney, Australia, describe the design process
for GBR 41, Girls on Film.
Peter Morton or ‘Morty’ as he’s affectionately
known is the founder of Wight Shipyard UK and
a good client of One2three Naval Architects in
the commercial high speed ferry arena. Together
we designed (and WSC built) the successful
Red Jet high speed ferries that operate daily on the
Southampton to Cowes route.
We’ve been colleagues and mates since 2014 and in that
time, we have assisted Morty in many of his maritime adventures,
so when he decided to design a 5.5 Metre he asked us to
provide technical support to UK designer David Hollom for what
would eventually become GBR 42 the current World Champion.
Somewhere along the way in the design process Morty
suggested that while we were analysing the three Hollom hull
candidates against the benchmark design that we might like to
“have a go” because while he intended to build new male mould and
tooling for 42, he had a spare deck, keel, rudder and parts from SUI
222 so he would consider building a second hull. So, we took on the
challenge and the boat was launched as Girls on Film GBR 41.
We leveraged off the GBR 42 project running in parallel, with the
structural engineering completed by Suzy Russell of Orca Consulting
and the project managed by Andrew Palfrey. Morty’s old friend
from the 1980s Tom Schnackenberg analysed the CFD studies,
performed in-house at One2three by Evan Spong, and confirmed the
results and the VPP predictions. David Heritage and his team built
the hull in Cowes. Sam Haines and Ruairidh Scott from North Sails
completed the awesome team of locally based UK designers with
One2three dialling it in from Australia.
After doing a rational assessment of the current champions
rating certificates our target concept was directed firmly at being
a good ‘all-rounder’ in the middle of the rule range, in terms of
displacement, sail area and waterline length, so that the boat
would perform well in all conditions.
DESIGN PROCESS
To start the design process, CFD analysis was run on five
different hull models. The benchmark was champion New Moon.
The other hulls tested were three designed by David Hollom, and
a One2three Naval Architects hull with emphasis on softening the
drag inducing hard chine knuckles and reducing wetted surface
area. The analysis was performed at both lightship and sailing
displacement. Identical appendages were added to the hull
models to compare righting moment at different angles of heel.
Heel angles 0, 10, 20, 30 degrees were run at a range of speeds,
to give a matrix of data for all five hulls to analyse, and to make
sure the hull performed well at all sailing angles.
The One2three hull was then refined at measurement points,
the bow was stylized, and a measurement check performed to
calculate sail area based on the 5.5 Metre rule.
A detailed weight estimate was performed to calculate the
longitudinal and vertical centres of gravity. A trim check was
completed to longitudinally position the keel and internal ballast.
The hydrodynamic and aerodynamic centres of effort were
56 • fivepointfive • APRIL 2023