Fluid Knowledge
Greg grew up by the sea and was privileged to enjoy all manner of sea and sky
sports. Hobbies included designing and experimenting with hydroplanes,
hydrofoils, seaplanes, rc gliders, robotic whales, birds and flying possums,
and led to studying Zoology, marine technology and fluid dynamics at Uni. Greg
has a practical and theoretical knowledge of fluid mechanics and water and aircraft.
This applies not just to craft designed by humans but also flying and swimming
organisms. Greg has designed and built full size ocean going artificial whales
, swimming sharks, and birds that actually fly in the air as gliders and
maneuver only using natural bird wing movements rather than flaps and ailerons.
The small radio control free swimming orca built as an experiment in the 1980s
was followed years later by a full size ocean going orca built for “Killers in Eden”.
Clicktop image for short Itza Cat video 1mb
Planing catamarans
Greg and Alex Cirrigottis developed the itza cat in the late 1970s whilst Greg
was still in High school. Unlike all other sailing catamarans on the market,
the itzacat had planing hulls rather than thin displacement hulls. This enabled
the cat to achieve extraordinary speeds around 20kts. The hulls are angled so
that the planing hull is flat on the water when the other hull is flying. Click
the second itza cat image for 2min fullscreen video 40mb quicktime .mov
Step Hulls
Greg, and Alex developed the planing hull catamaran further with a 17 foot long
step hull cat. The hull shape was based on Greg’s experimental experience and knowledge of seaplane floats. A stephull is a hull
with an abrupt change in level along its length so that when travelling at
speed, the water in contact with the bottom of the boat encounters air space
rather than boat bottom. A stephull travelling at speed may only have a small
percentage of its actual length in contact with the water generating friction,
whilst a conventional planing hull will have a large percentage constantly in
contact. A short wide section of planing surface is more efficient than a long
narrow surface. The step also allows the crew to manually adjust the pitch trim of the boat for different conditions. The ride quality of a flat bottom planing cat is much
harsher and bumpier than a displacement cat and is more like the ride of a
speed sailboard. Greg’s later StepHull designs incorporated Vee bottom and strakes to improve ride
quality and rig stability.
Greg design registered this craft in 1982. To the left is a fading photograph of
a twin masted model step-hull prototype from 1980 when Greg was in high school.
The 17 foot step cat incorporated a second step after the first step . The main step was fitted with
step ventilators leading from the deck so that air could rapidly fill the place
behind the step and allow the step to clear and the boat to plane quickly. With
the ventilators the transition to planing was preceeded by slurping and
gurgling noises similar to sucking on the bottom of a milkshake ! Photographs of the 17 foot step-hull cat will be posted as soon as they can be
tracked down!
Copy Cats ?
Sailing enthusiasts may note that the same logical step hull design principles
have been recently applied to a 60ft ocean racing sailing cat by French sailor Yves Parlier. Yves’ boat designer also was inspired by the fast and efficient hulls of Seaplanes.
To the lower left is an example of the high performance Step-hull sailboards
shaped by Greg’s brother Bruce McKee based on Greg’s research of seaplane and racing hydroplane step hulls.
These boards from 1988 have astonishing performance and suffer far less from the
drag increases due to the porpoising or pitch variations of conventional
boards. They incorporate tunnel hulls trapping air beneath them and run on only two or three points of minimum wetted
surface area when at speed. These craft all have very sharp edges to their
planing surfaces so that spray is cleanly released and thrown outwards rather
than clinging to the sides as occurs on round bildge craft. The larger yellow board features step ventilators to facilitate rapid transition
onto the step.
Wakeboards
Water sports enthusiasts may be interested to note that Greg’s brother Bruce, besides being one of the world’s top Surfboard shapers and innovators also produced the world’s first production wakeboard in the early 1980s, the McSki or SSS skiboard.
Videos (require quicktime)
Early 1980s experiments
Robotic swimming Sharks 5MB .mov
Flying Rainbow Lorrikeet 1.6MB .mov
(extreme language warning) 1980s
Own Design Aerobatic seaplane. First ever attempt at designing or flying an RC
powered plane 1980.
The float design similar to Greg’s sailing craft
Swept forwards wing canard with NACA 66-012 laminar flow symetrical section
fuselage and wings. Designed in 1985
Sculpted and built by Greg, this full sized replica of “Old Tom” can dive and surface and has a working blowhole. It is on location here in
Twofold bay, Eden.
An animatronic great white able to operate in sea water alongside real sharks.
Click image for Video
A full sized Humback submersible built for a television series and operated in
open ocean.
It is a fully operational wet submarine.
The full size replica of Old Tom in Eden about to dive. The streamlined form of
the orca weighs around 6 tonnes yet is maneuverable and quite easy to
accelerate to speed. A real orca can swim at speeds up to 60km/hr . Fast enough
to barefoot waterski behind.
A different Great White to the one above, this version sculpted by Paul Trefry
and painted in silicone by Greg.
This free swimming radio control submarine model of Old Tom was made in 1985 and
maneuvers in the same manner as a real orca, using tail and pectoral flukes.
The body shape of an orca is a low drag, natural laminar flow form similar to a
naca 66-020 airfoil section.
This forward swept wing canard uses the tuna fish like naca 66-012 laminar flow
sections for all flying surfaces and fuselage. It is extremely aerobatic and
has identical performance flying upside-down as right way up. The extremely low
drag gives it very high speed despite having no engine.. Unstallable in normal
flight
Tandem wing design verification model made in 1986 during Aeronautical
engineering study at Uni. The fuselage form is based on the laminar flow naca 66-018 airfoil section found in the bodies of Tuna fish, and
similar to the Orca above.
The high speed design is hand launched at Dobroyd lookout in Sydney. The front
forward swept wing has the same wing area as the rear wing and controls pitch.
