Hybrid Hulls
UMaine engineers helping the U.S. Navy to build lighter, faster
boats using composite materials
The U.S. Navy is exploring the
technology for a new generation of high-speed support ships with the
help of the University of Maine and companies in Maine, Hawaii and
England.
The vessels would combine traditional steel infrastructure with
underwater bodies or hulls made of composite materials. The resulting
hybrid could lead to ships that meet the Navy's needs for faster and
lighter mid-size vessels, says Associate Professor of Mechanical
Engineering Vince Caccese, UMaine's project coordinator. The technology
also could have civilian applications.
This Modular Advanced Composite Hull Form project, known as MACH, has
attracted more than $4.5 million in federal funding, as well as support
from U.S. Navy research labs. The Navy takes a conservative approach to
ship design, and every aspect of the new technology must meet stringent
performance criteria.
"The idea here is to use a metallic skeleton and a composite skin," says
Caccese, whose research has included testing joint designs and composite
structures for government agencies such as NASA and companies from
Maine-based Bath Iron Works to Aegis Bicycles. "Whenever you do anything
below the waterline, it's risky. You need to make sure that whatever you
do doesn't leak. We're being cautious, looking at different kinds of
joints (between composite and steel)."
Composite materials, such as glass fiber-reinforced polymers and
high-strength carbon fibers, have long been used in racing yachts and
other marine crafts. In the last decade, Scandinavian boat builders have
extended that technology to military purposes.
|
University of Maine mechanical engineer Keith Berube makes composite
panels in Crosby Laboratory. The manufacturing process uses multiple
layers of fiberglass fabric and synthetic resins.
|
The inspiration for MACH comes from the
Navatek division of Pacific Marine and Supply Company, a shipbuilder in
Hawaii. Like the technology behind hydrofoils — boats that ride above
the waves on wing-like panels below the water — MACH vessels would
incorporate sleek underwater structures that, while moving, could lift
most of the ship out of the water. Power would come from an electric
motor that also rides under the ship.
"Pacific Marine found that using an underwater body could result in a
dramatic increase in speed using the same horsepower. This approach gets
a lot of the ship out of the water and reduces drag," says Caccese.
Partners in the project include Pacific Marine in Honolulu; Applied
Thermal Sciences, an engineering consulting firm in Sanford, Maine; and
Nigel Gee and Associates, a naval architecture firm in Southampton,
United Kingdom; as well as U.S. Navy labs in Maryland and Rhode Island.
At the University of Maine, students are collaborating with faculty and
professional engineers to design, build and test hybrid hulls that can
withstand underwater speeds of 50 knots or more. The challenge is to
increase structure strength through the manner in which the composite
panels are fastened to the internal steel frame. Moreover, the hull must
be easily manufactured and maintained — all at a cost the Navy can
afford.
In addition to UMaine mechanical engineers, electrical and computer
engineering professor Bruce Segee is leading a team that is developing a
computing and data management system to monitor structural stresses in
the hull and relay information to the ship's crew. Their approach uses
sensors that are built into the panels.
The idea is to give the crew an immediate view of the hull structure.
"Our focus is computing power and networking so that multiple sensors
can be placed inside the panel, but the number of wires going to the
panel remains small and independent of the number of sensors. All you
need for the electronics is power, ground and a network connection,"
says Segee.
Many of the experimental composite parts are being designed and made
from scratch. Working with engineers Keith Berube and Randy Bragg,
students use a process known as resin transfer molding to make panels of
different shapes. As many as 16 sheets of woven fiberglass fabric may go
into a single panel. Liquid resin the color and consistency of maple
syrup is pumped through the fabric layers. One panel can be made in
about a day.
The dry composite panels are studied in UMaine's Mechanical Engineering
Structural Testing Lab in Boardman Hall. There they are bolted to steel
I-beams; then the joints are stressed to determine just how much
pressure they can withstand without bending or breaking.
The tests have produced some interesting results. In one case, applying
a high force bent the three-quarter-inch-thick steel structure,
demonstrating the strength of the undamaged composite. In others, cracks
in the panels helped the engineers determine how stress is distributed
in the bolted hybrid connections. Before they are done, the UMaine
engineers will study dozens of panels and I-beam joints.
While steel hulls are still essential for large naval vessels, Caccese
sees a bright future for hybrid structures on smaller ships. Composite
hulls are lighter, allowing for greater fuel efficiency and heavier
payloads. Composites also are the materials of choice for stealth
technology intended to avoid detection by radar.
With MACH, UMaine engineers and their partners are pushing shipbuilding
into uncharted waters. It will be a long-term effort, says Caccese, with
the potential to transform the nation's maritime industries.
by Nick Houtman
May-June, 2003
Click Here
for more stories from this issue of UMaine Today Magazine.
