Feature Article
Feature article on yacht repair and refitting written by Richard
Stewart for July 2000 issue of Composites Technology magazine.
YACHT REFITTING INCREASES VALUE
AND PERFORMANCERefit & repair yards flourish, meeting demand from growing fleet.
By Richard Stewart
The worldwide fleet of large private yachts is growing, causing
an increase in the number of repair and refit yards dedicated to
this segment of the marine industry. Older fiberglass vessels are
increasingly being refit for various reasons – to trim weight, add
living space, improve performance – all of which enhance the
owner's enjoyment and the yacht's value. Marine experts at the
recent International Marine Repair & Refit Exhibition & Confer-
ence (IMREX 2000) shared case histories of projects and
provided options and solutions for yacht owners and managers.Refitting for speed is one of the most common rebuilding pro-
jects. That can involve simply streamlining the underwater
running gear and re-powering the yacht with a more efficient,
higher-performance propulsion package. It can also include
extending the hull and replacing solid-wood bulkheads, decks,
overheads and other structural panels with cored composite
materials to minimize weight. For sailboats, it might also mean
replacing masts of aluminum or wood with carbon fiber.Any boat can benefit from fewer pounds per square foot on
the bottom, according to Rick Hyer, Engineering Manager,
Chris-Craft Boats (Sarasota, Fla.). “More planing surface is
always desirable, especially in a highly loaded bottom,” he
says, noting that benefits can be realized in ways other than
just added top-end speed.Such was the case with a project that involved extending the
hull of a 50-foot motor yacht by five feet, adding 4,000 lbs.
in the process. Attention was paid to minimizing weight in the
construction, then redistributing the weight to adjust the vessel
for proper balance. The result was a longer boat that ran as
fast as it had before the extension, but with the same power.
And it ran easier, Hyer notes. The boat achieved better fuel
economy than before the refit and it had better characteristics
throughout the power range.He recommends using composite materials to reduce weight
in a refit as long as the additional cost can be justified.
“Graphite/Kevlar/hybrid products commonly used in go-fast
boats normally are not selected for use in motor yacht con-
struction,” he says. The price differential for such exotic
materials does not generally make sense for motor yachts.
Conventional glass-reinforced composites and sandwich
panels are better bets, Hyer feels.The interior is a good place to spend some money to save
weight, observes Hyer, since interiors account for as much
as 30 percent of the average luxury yacht's gross weight.
Fiberglass-skinned, balsa-cored panels cost about three times
as much as sheets of ¾” marine plywood, but they weigh
about half as much. Honeycomb-core panels, while costing
more, weigh even less than balsa. Common sense should
prevail in the refit when justifying the cost of materials, he feels.“Substituting the exotics and hybrid composites for more
inexpensive conventional composite materials might save
1,000 lbs. on a project,” notes Hyer, “but at a 500 percent
price premium. Spending that kind of money to save 1,000 lb.
on a 60-foot yacht displacing 80,000 lbs. certainly doesn't
make sense.”EXTENDING THE HULL
ADDS SPACE, VALUEExtending the hull has become a common refit operation,
especially for older motor yachts with squared-off rear
sections or transoms. An extension can create flowing
lines to update the appearance of the yacht for higher resale
value, while providing more deck and storage space,
according to Andre Cocquyt, a marine consultant and
owner of Stuart Catamarans (Stuart, Fla.).“There's very little you can do on the bow or the pilot house
of a yacht to change the look dramatically. So the creativity
is mostly expressed in the aft deck and the transom,” he says.
For most yachts in the 45' to 70' range, Cocquyt does not
recommend extending the waterline much beyond 10% of the
original length due to adverse affects on the vessel's trim and
handling characteristics caused by longer extensions.The least expensive type of extension is the addition of a
swim platform or an open cockpit to the original transom. A
more complex project might include curving staircases and
an overhang over the extended section. In either case, the
extension must be as structurally sound as the original hull,
notes Cocquyt.Original drawings are used to determine the vessel's FRP
laminate schedule, which is closely followed to mold the new
section. Panel stiffness of the extension should be similar to
that of the yacht's panels, otherwise stress lines can develop
at the connecting point, he explains. Longitudinal stringers or
reinforcements in the hull section of the extension extend into
the yacht's hull and are bonded to its stringer system.Laid up using fiberglass mat and woven material, the extension
is commonly completed before the yacht arrives at the boat
yard, notes Cocquyt, reducing time required in dry-dock.
Molds to produce extensions for the more popular yachts are
kept on hand for ready use at larger boat yards. A typical hull
laminate consists of ¼” of fiberglass on both sides of 1½”-thick
foam core panels. Once the extension is joined to the yacht, a
temporary female mold is used to develop a fair and continuous
extension of the hull and topsides.
COMPOSITES VALUED FOR
LIGHTWEIGHTING INTERIORSStructural sandwich panels are commonly used in marine refits.
The panels are a layered construction that sandwiches two
strong thin facings with a core that is strong and stiff enough to
hold the facings flat. These outer skins, which typically are
sheets of FRP, are bonded to the core material to carry the
compression and tension loads. The core and the adhesive that
bonds the laminate carry the shear loads. The core can be of
foam, balsa wood, or a honeycomb structure made of paper,
plastic, aluminum or other material that provides sufficient
shearing resistance for the application.The use of cored panels for interior bulkheads, partitions,
overheads and floors can save significant weight and provide
excellent stiffness. In addition, plastic honeycomb sandwich
panels, such as those from Nide-Core Corp. (Palm City, Fla.),
extruded from polypropylene, provide superior acoustic and
vibration insulation qualities.The galley is a good candidate for lightweighting with composites,
relates Cocquyt, who has extensive experience in structural
repairs and refits. Corian, Avonite and other solid surface
materials typically used for countertops are the heaviest part of
any galley installation, he says. These materials, which weigh an
average of five lbs./ft2 , are usually installed on top of marine
plywood, adding another 2 lbs./ft2 . Cored composite panels
make an excellent substitute. Using fiberglass-faced aluminum
honeycomb-cored panels can provide the required strength but
with a weight reduction of 3-4 lbs./ft2, relates Cocquyt.He recently completed a U-shaped galley counter top using a
polyester methacrylate polymer in liquid form that can be
poured, sprayed or brushed over top of a 1-1/4” thick fiber-
glass/Nomex® honeycomb-cored panel. The finished counter
weighs just over 20 ounces per square foot and looks and feels
as good as the more traditional surface materials, he says.Cored panels offer the fabricator a degree of freedom that is
difficult to achieve through traditional carpentry and joinery
work, but proper training is important for employees who are
new to working with these materials. “Even experienced
carpenters and furniture makers tend to use the panels as they
would use plywood,” Cocquyt observes, noting that gains
possible with cored panels come not only from their light
weight but also from their inherent stiffness.“A lot less internal structure is needed with cored panels,” says
Cocquyt. “Radii can be made very fast by cutting and bending
the panel rather than fabricating solid-wood corner posts. But
because of the complexity and perhaps unfamiliar techniques
required to work with cored panels, they are not recommended
for every job,” he adds. A small square-cornered cabinet of
less than 10 ft2 total surface – requiring inserts, cleats and edge
finishing if cored panels are used – would not be worth the extra
time and effort it takes to save only a few pounds, notes Cocuyt.
On the other hand, for larger surfaces that need less substructure,
using cored panels can save significant time and weight.The mating of FRP and honeycomb makes a perfect marriage
for lightweight structural panels because each product enhances
the properties of the other, according to Tricel Honeycomb Corp.
(Gurnee, Ill.), which manufactures panels with Kraft paper honey-
comb core – a kind of “super-corrugated material.” Honeycomb,
when properly applied during the lamination process, can increase
the beam strength of solid FRP by as much as ten times. A
honeycomb core panel can also save considerable glass and
resin when compared with a solid FRP panel, yet still increase
beam strength, the company relates.Before starting a refit project, Cocuyt recommends sitting down
with the boat owner and other decision-makers to discuss the
choice of materials. “Never forget that the client has the final say.
The role of the technician is to do his best with the given para-
meters, not to alter the parameters,” he says. “If the client wants
inch-thick onyx or other materials that affect the weight of the
yacht, that's his choice. But it is our job is to inform him about
the consequences and suggest alternatives.”EXTENDING THE HULL
ADDS SPACE, VALUEExtending the hull has become a common refit operation,
especially for older motor yachts with squared-off rear sections
or transoms. An extension can create flowing lines to update
the appearance of the yacht for higher resale value, while
providing more deck and storage space, according to Cocquyt.“There's very little you can do on the bow or the pilot house
of a yacht to change the look dramatically. So the creativity is
mostly expressed in the aft deck and the transom,” he says.
For most yachts in the 45' to 70' range, Cocquyt does not
recommend extending the waterline much beyond 10% of the
original length due to adverse affects on the vessel's trim and
handling characteristics caused by longer extensions.The least expensive type of extension is the addition of a swim
platform or an open cockpit to the original transom. A more
complex project might include curving staircases and an overhang
over the extended section. In either case, the extension must be
as structurally sound as the original hull, notes Cocquyt.Original drawings are used to determine the vessel's FRP
laminate schedule, which is closely followed to mold the new
section. Panel stiffness of the extension should be similar to that
of the yacht's panels, otherwise stress lines can develop at the
connecting point, he explains. Longitudinal stringers or reinforce-
ments in the hull section of the extension extend into the yacht's
hull and are bonded to its stringer system.Laid up using fiberglass mat and woven material, the extension is
commonly completed before the yacht arrives at the boat yard,
notes Cocquyt, reducing time required in dry-dock. Molds to
produce extensions for the more popular yachts are kept on hand
for ready use at larger boat yards. A typical hull laminate consists
of a quarter-inch of fiberglass on both sides of inch and a half
thick foam core panels. Once the extension is joined to the yacht,
a temporary female mold is used to develop a fair and continuous
extension of the hull and topsides.REFITTING SAILBOATS
WITH CARBON MASTSA refit designed to improve the performance of a sailboat is the
replacement of the mast with one molded of carbon fiber. A
carbon mast offers less weight aloft, which lowers the boat's
center of gravity and results in a more stable platform, according
to Ben Sprague of Goetz Marine Technology (Bristol, R.I.).
Typically 30-35 percent lighter than aluminum, a carbon fiber
mast produces more power from the sails in light winds. The
reduced weight also allows a boat to be refit with a taller mast
to provide increased sail-carrying capacity for even more perfor-
mance, while still saving weight over the original mast.Goetz increased the rig height on a 1913 Herreshoff P-Class
yacht by 12 feet using a carbon mast, yet still saved about 500 lbs.,
reports Sprague. An Alden 58' yacht was refit with a carbon
mast of the same height as the original but with an internal sail-
furling system in the mast. The weight savings was 540 lbs. over
a comparable aluminum furling mast. Owners claim that boats
refit with carbon masts sail faster upwind, heel less, right them-
selves quicker when hit with gusts and are quieter than aluminum
masts.Pound for pound, carbon fiber spars, including masts, booms
and spinnaker poles, are nine times stronger than aluminum and
15 percent stiffer than aluminum, according to Sprague. The
wall thickness of carbon spars can be increased to add reinforce-
ment wherever needed – something that is not possible with
extruded aluminum spars. Carbon masts and booms have grown
in popularity among racing enthusiasts due to the strength and
stiffness they offer. Carbon masts can withstand knockdowns
in heavy wind that typically snap or crumple aluminum masts.In terms of cost, a carbon mast is roughly three times more
expensive than a standard aluminum mast, says Sprague, who
notes that the differential varies depending on the quality of the
aluminum version. Compared to the cost of a high-quality custom
aluminum mast, carbon fiber might cost only 60 percent more, he
notes. For a 40-foot boat, a fully rigged carbon mast might cost
$18,000-$20,000.Most carbon fiber masts are hand layed up with unidirectional
carbon fiber/epoxy prepreg over male mandrels. The mandrel is
extracted after the tube is cured with heat, either under vacuum-
bag pressure or in an autoclave. Female (concave) molds are also
used, producing two halves that are joined together to complete
the mast, creating glue-lines and overlapping seams. A benefit of
male molding is that the composite material is not interrupted by
joints around the circumference. However, the mandrel can be
difficult to remove from long masts. Some carbon spar manufac-
turers prefer the female molding process for very long masts.
CARBON SPARS PRODUCED
TO AEROSPACE STANDARDSHall Spars (Bristol, R.I.), another manufacturer of carbon fiber
spars, favors male mold layup and autoclave curing. High-
modulus carbon fiber prepreg is typically used for masts of
high-performance racing boats because of the increased stiffness-
to-weight ratio that it provides over standard-modulus carbon.
The cost of high-modulus carbon may not be justified for all mast
applications, however. The company recommends a cost-benefit
analysis before the customer selects which material to use.A computerized spar design program and Finite Element Analysis
(FEA) software are used by Hall Spars to engineer carbon fiber
masts and booms. FEA models determine critical loads and the
location of maximum stresses caused by the loads, enabling the
designer to specify section wall thickness and reinforcement points
accurately. This technology produces spars that are not excessively
heavy or so light that they can fail in heavy winds.The composites department of Hall Spars contains two mast
mandrel rotating machines. One is capable of molding masts as
long as 80', the other has a 140-foot capacity. The centerpiece
of the shop is a 63-foot-long purpose-built autoclave with an
inside diameter large enough to cure a racecar.All carbon spars produced by Hall are cured at 250 degrees F.
at 6 atmospheres (85-100 psi). Composites cured in an autoclave
are as much as 50 percent stronger in compression than those
formed under vacuum pressure alone, the company says. The
autoclave almost entirely removes strength-sapping voids in the
laminate. The pressure of the autoclave produces smooth finishes
on the outer surfaces of the molded spars.After the composite tubes are cured, they move to the pre-paint
assembly department, where components such as masthead fittings,
tracks, spreaders and other parts are attached. The spars are sent
to an outside paint facility to be coated with a hard, durable
Awlgrip® finish, a product of U.S. Paint Corp. (St. Louis, Mo.)
After coating, the spars are returned to Hall for final assembly and
attachment of the mast rigging before shipment.DOCUMENTING REPAIR
PROCESS RECOMMENDEDAnother seminar at the IMREX conference covered the impor-
tance of involving the customer from the earliest stages of a repair
or refit project and of thoroughly documenting all stages of the
job. The documentation assures that the job was done right. As
part of the yacht's permanent record, it is also valuable for resale
purposes. Documentation of the work is especially important
on hull repairs and hull extensions of boats constructed with
cored composites, which can be complex, says Dana Green-
wood, Director of Engineering and Manufacturing, Luhrs/Mainship
Corp. (Palm Coast, Fla.)Digital cameras are finding widespread acceptance at marine
repair and refit facilities to produce documentation packages that
can be submitted to the customer on a set of CD-ROM disks.
Each ply of the repair or refit should be recorded as it is laid up
so that there can be no disputes about the laminate schedule,
joints and overlaps after fairing material is applied over the
repaired area. Complete tap-test data should also be included
in the documentation to show the extent of damage before a
repair is started, Greenwood feels.For hull extensions, he recommends having the vessel surveyed
by an independent surveyor. The report establishes the original
performance, handling and noise levels as well as other factors
present before the work is undertaken. That information is useful
in case the owner comes back after the project is finished to
complain that the boat is noisier or slower or exhibits some other
negative performance characteristics that were not evident before
the work was done. The survey should identify sea conditions,
wind, depth of water and load – all of which can have a signifi-
cant effect on performance. Knowing the conditions encountered
during the survey can prove useful in an evaluation during sea trials
after the project is completed.The survey will also establish the vessel's true dimensions, which
can be different from those stated by the manufacturer, notes
Greenwood. A boat purchased as a 42-footer might only measure
40½ or 41 feet long, something the owner should be aware of
before the marine facility starts a five-foot extension project that
the owner expects to result in a 47-footer – and ends up short.Greenwood's advice to marine repair and refit facility operators:
“Being smart is knowing what you're dumb at.” That means hiring
specialists and subcontractors to handle aspects of a project that
the facility is not experienced enough in or fully equipped to deal
with in a professional manner. Refitting and repairing large yachts
has become big business for many marine facilities. Costs of these
projects are high, and the consequences can be significant for a
boatyard that fails to protect itself from unsubstantiated claims of
boat owners or managers.
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