Project Brighter World
By John R. Marples
In early 2007 Impossible Pictures of London,
U.K. approached me to participate in a boat
demonstration using a Flettner* rotor powered
trimaran. They were filming a demonstration
for the Discovery Channel's Project
Earth series. Our program would be called
Brighter World. Two atmospheric scientists,
John Latham and Stephen Salter, had devised
the Albedo effect, a way of changing the reflectivity
of clouds to deflect some of the
sun's heat, cooling the oceans. It required a
flotilla of vessels to seed clouds with small
saltwater particles. Our trimaran would be a
prototype for this type of vessel.
(*A Flettner rotor is designed
to use something
called the Magnus effect
for propulsion. The
Magnus effect is a force
acting on a spinning body
in a moving airstream that
acts perpendicular to the
direction of the airstream.
It gives the pitched baseball
its curve, the golf ball
The scheme called for installing a couple of
specially built rotors on a boat. We purchased
a used Searunner 34 power trimaran
(a boat I co-designed with Jim Brown in the
1970s) in Florida and trucked to our building
site in Fort Pierce, on Florida's eastern
coast. We chose the location for its access to
Tim Ziel installing the sheet metal mold surface on the mold framework. We replaced the Cleco fasteners with pop rivets after fitting.
The sheet metal pieces were butted together on each mold former.
We built two 4.5' diameter rotors. The forward
(main) one was 27' long and the aft
(mizzen) was 21' long. They were sized and
positioned to center the lift in a similar place
to the sail-powered version of the Searunner
34. A 48 DC electric motor (golf cart motor)
powered each rotor from a bank of batteries
wired through a speed controller. The controller
throttle access was conveniently positioned
in the cockpit for the helmsmen. Battery
charging required a shore power plug-in
at the dock.
Each rotor was a large, smooth cylinder, supported
by ball and roller bearings. In addition,
fences - 8' diameter discs- were added
to the cylinder about 3' apart to improve lift
performance. Since the surface area of the
fences and cylinder was quite large, we chose
a foam/carbon fiber sandwich construction
to keep the weight down. We made each cylinder
in a cylinder mold in four longitudinal
sections with joggle seams at the joints. Coring
foam was beveled at the edges and omitted
at the joints and bulkhead attachment areas.
The 27'-long panels weighed about 25 lb
and the 21'-long panel about 19 lb.
The rotors were supported on the boat by
aluminum tube stub masts that went half way
up the rotor to the mid bulkhead. A pin on
the mast top supported a roller bearing, carrying
the full weight of the rotor. Another
larger ball bearing at the bottom maintained
the rotor alignment on the mast and provided
an attachment point for the cog belt
drive system. We added major structural reinforcement
to the boat deck, cabin top and
flooring to support the weight and bending
moment of the rotors. It was crudely done
using multiple layers of plywood to resist the
side loads created by the rotor lift.
The cylinder mold
Panel construction employed a metal surface,
partial cylinder mold and vacuum bag layup.
Cylindrical accuracy for the finished rotor
was crucial since it was intended to operate
at 400 rpm. (That equates to a surface speed
of about 65 miles per hour.) Minor weight
differences between panels could cause significant
imbalances in the finished rotating
structure, so we need the lay-up consistency
to be as accurate as possible.
We chose MDF sheets and aluminum for the
mold structure and surface to assure accuracy
of the component parts. Using cutting
fixtures, we made the MDF formers identical.
The radius was rough cut and then
trimmed with a router on a pivot arm. We
assembled the sidewalls full length, keeping
the lower edge perfectly straight. All formers
were screw fastened to the sidewalls on 4'
centers and registered with the lower edge.
The upper corners of the radius cutout were
sighted to check optical alignment of the
formers. Then the aluminum square tube
stringers were screw fastened into notches in
the formers and adjusted to make sure the
inside surface touched the radius. Small
wood wedges were driven under the sidewall
for adjustments to level the mold assembly.
We tried to verify the alignment with a laser
level, but it was not sufficiently accurate for
our needs. Once the mold was adjusted, but
before we installed the sheet metal surface, it
was glued to the floor.
The mold surface was .040 aluminum sheets, 4'
wide by 6' long. Each sheet was butted to its
neighbor, with the butts centered on a mold
former. The sheets were merely pressed against
the formers and stringers, and pop-riveted to
the top two stringers. Self-adhesive aluminum
foil tape was used to cover the butt joints on
the molding surface, rendering them air-tight.
The foil tape was very thin and when burnished,
was less than the thickness of a coat of
paint. Sunlight reflections on the mold surface
indicated it was very smooth and fair.
To prepare the mold for operation we
mapped out the panel size on the mold surface
and also marked off the vacuum seal locations.
We also glued a strip of .040 aluminum
sheet about 2" wide to the mold to create
the joggle on one edge of the panel. Then
we gave the molding surface five coats of
mold release, hand rubbing each coat to insure
a non-stick surface.
The panel construction consisted of 6 oz
plain weave carbon fiber cloth on each side
of ½"-thick H-80 Divinycel contour core foam. We started the layup with nylon release fabric against the mold, then used
squeegees and roller to wet out carbon fiber
cloth. The foam core was precut to dimension
and coated with a light mixture of epoxy
and 407 Low-Density Filler to fill the
surface voids. We transferred the wet foam
onto the carbon cloth and positioned it.
A panel curing under
vacuum. The panel was
built of ½"-thick
Divinycel foam between
layers of 6 oz carbon fiber
cloth laminated with
WEST SYSTEM Epoxy.
The cured outer carbon
skin with foam core.
Finished panels being
prepped for final assembly.
The first panel joint
was held in place with
Cleco fasteners onto a
stringer after the sheet
metal had been removed.
The middle bulkhead
with main bearing attached.
had cables connected to
the lower bulkhead rim
to carry the cylinder
That was followed by release fabric, baby blanket (quilt batting) and finally, the bag (4-mil poly film). The vacuum manifold was already in place and covered with masking tape. We
pulled the tape off the manifold and the vacuum
seal and attached the bag, with the
pump running. Soon the bag was compressing
all layers and the vacuum gauge normally
showed about 23" of vacuum.
The rotor assembly
Each rotor was made from four panels longitudinally
fastened with epoxy. To prep the individual
panels we scuffed the bonding surfaces
and trim the panels to exact size. We removed
the sheet metal mold surface and fastened the
panels for the first joint to one of the aluminum
square tube stringers with Cleco fasteners.
The mold formers and perfectly straight
stringer accurately kept the cylinder shape
while the epoxy cured. Next, the three ½" plywood
bulkheads were positioned and epoxied
in place, followed by a third panel. Next we
added more ring frames and mechanical gear,
then glued the last panel in place. All the longitudinal
joints used Cleco fasteners to position
and clamp the panels together during epoxy
cure. They worked very well as long as they
were oiled before use to prevent epoxy from
clogging the moving parts.
All three bulkheads installed
and a third panel
Ring frames and other
mechanical gear installed
before the forth
panel was added.
Rotor roll-out. Pipe rollers
make it easy to move
the rotor into position
for transport. It was
then lifted onto a trailer
by a crane.
The rotor is lifted by the
eye-bolt in the top bulkhead.
Note the "tilt-up
fixture" to prevent damage
to the fences.
Experimental work published by Thom in
the 1930s showed a significant increase in
lift created by the rotor if large discs were
added. We duplicated his work on our rotors
with 8' diameter discs added on 3' centers.
Each disc had the same layup schedule as the
rotors and was made on a special round table.
A router on a pivot arm was used to trim
the fences and maintain dimensional accuracy.
With the rotors supported on a rotation
fixture in the shop, the fences were positioned,
wedged in place and adjusted to run
true by slowly rotating the rotor. Once adjusted,
they were glued in place with large
epoxy fillets on both sides. We painted the
assembly while it was still on the fixture.
A crane lifted the rotors into position and
slowly them lowered onto the mast. We did
this early in the morning before the wind
came up. The rotors had to be threaded onto
the mast perfectly vertically so that the bearing
pin at the masthead would engage the
bearing bore on the middle bulkhead, which
was only 1½" diameter. The bearing pin had
a machined "dunce cap" nut to help hit the
target bore. It all worked very smoothly,
thanks to the expertise of the crane operator.
The drive system
Each rotor was powered by a 10 hp, 48-volt
electric motor with a speed controller and a
bank of 6-volt batteries. The motors were
mounted to the mast on clamp brackets of
welded aluminum. A cog belt using pulleys
to achieve the correct speed ratio spun the
rotors at 400 rpm maximum. The system
worked very well without any adjustment
from the first run. The initial design called
for the boat to be carpeted with photo-voltaic
panels to charge the batteries, but we did
not have the money or the time to install
We towed the boat about a mile offshore in
light winds for the demonstration. At first, the
boat bounced around in the light chop and
swells, but as soon as the rotors started turning,
the boat stabilized and became very
smooth. We achieved 6 knots boat speed in 6
knots of wind at the best run of the day.
Kevin, the "presenter" put aboard for the
filming, was initially rather skeptical about the
boat's potential. But by the day's end he ran
out of superlatives to describe the performance.
The whole crew was pleased with the
show. The demonstration sailed with about 8
hours of powering time for a single charge on
the batteries. Since the winds were light and
the rotors only rotated to less than 200 rpm,
we had over 12 hours of running time.
The rotors were lowered
carefully over the stub
masts. The mizzen rotor
is being installed. The
main rotor is already in
The 10 hp drive motor
is clamped to a
bracket on the mast.
A cog belt drive system
to rotor. It worked
Demonstration day. The boat performed very
well, sailing at wind speed, even though it
was about 30% heavier (due to the heavy batteries)
than the normal sailing vessel design
weight. The project was considered a tremendous
Epoxyworks 29 / Fall 2009
Copyright © 2009, Gougeon Brothers, Inc. All rights reserved.
Reproduction in any form, in whole or in part, is expressly forbidden without the consent of the publisher. EPOXYWORKS, Gougeon Brothers, WEST SYSTEM, Episize, Scarffer and Microlight as used throughout this publication, are trademarks of Gougeon Brothers, Inc., Bay City, Michigan, USA.