The first thing you will ask your naval architect is what material you want to use to build your new yacht. He has to know before putting pencil
to paper or cursor to computer screen: Weight calculations, interior volume, horsepower, tankage, sail area, ballast-- all depend on the
material. Already you have to make a decision, the first of many; some people think it's also the hardest. It's really the easiest, once you know
the facts.
You have three options: steel, aluminum, or fiberglass. Each has advantages for specific applications: You can't beat fiberglass for production
boat-building, for example, where dozens, maybe hundreds of similar boats of adequate quality will be built using one set of expensive tooling.
Steel, on the other hand, is the default choice for very large hulls where high strength and stiffness must be combined with a manageable plate
thickness, and weight isn't such a factor. Between these extremes, it's the buyer's choice.
The more yacht-club "experts" you ask, the more confused you get. But after you do some research of your own, read the articles, talk to builders
and naval architects, read more articles, even hang out with professional captains, your choice is obvious.
It's aluminum. Here's why:
Aluminum combines light weight, high strength, easy workability, and acceptable cost in one package. Steel is less expensive as a raw material,
but by the time the extra dollars associated with handling it, forming the plates, etc., are factored-in, much of that advantage disappears.
Steel takes longer to weld than aluminum an increases labor costs. It must be sandblasted before priming and painting, another expense; it's
high- maintenance, which translates to increased operating costs; and it's heavy, so less displacement is left over for the 1,001 other things
that must go into a first-class yacht-- things like engines, systems, and fuel. Steel isn't a serious player in this league--leave it for only
the largest yachts or commercial boats.
Fiberglass usually means a skins-and-core composite that creates panel stiffness without excessive weight. Cored composites are relative
newcomers in the custom- yacht field and vary in quality from excellent to abysmal. Trouble is, you don't know which level you're getting because
it's impossible to analyze a composite laminate thoroughly without destroying it. You have to rely on the reputation and track record of the
builder, and hope that everyone is having a good day when they lay up your hull.
In the hands of expert craftsmen working in climate-controlled shops, using high-tech autoclaves, post-cure ovens, and exotic fabrics, cores, and
resins, composite FG produces a strong, light laminate. The aerospace industry uses lots of carbon fiber and epoxy; supersonic fighter planes,
airliners,and the Stealth Bomber soar on carbon. Laminate costs soar, too, often 20 times higher per pound than boat-builders are willing to
spend, and yacht buyers willing to pay, for marine composites.
And you get what you pay for: Composites assembled by even the best yacht builders can suffer delamination, incomplete cure, resin starvation,
water absorption and heat deformation. Finish your hull in Flag Blue or another dark color, and it can lose up to 75% of its strength under the
hot Florida sun. According to one classification-society engineer, it's likely that cored-composite yachts built with bottom-of-the-barrel raw
materials like E-glass fabric and polyester resin will have water in the core within five years. Even more troublesome is secondary bonding: the
attachment of bulkheads, stringers, floors and other structural members to the cured hull. Secondary-bonding failure is a major cause of
composite boat owner's headaches. Composite fiberglass is floating Russian roulette--do you feel lucky?
Boat-building in aluminum doesn't involve luck. It's a straightforward process using easily tested, time-proven materials and methods. On a
weight-for-weight basis, aluminum alloy is stronger than steel. Strength-for-strength, it weighs about half as much and is 10 times more
resilient. Collisions that would puncture steel or composite hulls often just dent aluminum ones. Rather than starting the pumps, the skipper has
the yard cut out the dimple and weld-in a new plate the next time its' there for routine maintenance. Nobody takes an unplanned swim, nor does
the yacht suffer any downtime.
Aluminum, as defined by SOLAS standards, is non-flammable and non-combustible. Because of this, aluminum yachts can be made to comply to new,
more strict I.M.O. commercial boat rules that are nevertheless appropriate for all oceangoing vessels. These rules demand structural fire
protection (containment of fire in a particular compartment by the vessel's structure only without help from firefighting systems) and multiple
watertight compartments. While watertight bulkheads can be built in composite yachts, structural fire protection is problematic, since composite
cannot meet the relevant standards. While these new rules are mandatory for high-speed commercial boats in international service only, a
yachtsman planning long cruises far from land can see the advantage of a yacht that's sink-and-fire-resistant.
The 5000-series alloy used to build modern aluminum boats consists of aluminum and magnesium, with a trace of silicon. Sailboat masts and spars
are usually anodized 6061 alloy and contains a little copper, as well. Copper increases strength but reduces corrosion resistance: The copper in
the 6061 reacts with the aluminum when salt water, or even salty dampness, is present to serve as an electrolyte. This causes bubbles to form
wherever there's a break in the paint film and salt gets underneath. The result: Lifted paint, powdery white corrosion pockets, and other
maintenance nightmares. Unfortunately, many yachtsmen carry this image with them when they think about building an aluminum boat, but the
5000-series alloys are much more corrosion- resistant because they contain no copper.
At Palmer Johnson, a 78-year-old custom yacht-building firm in the tight-knit community of Sturgeon Bay, Wisconsin, they insulate every dissimilar
metal fitting and fastening from the aluminum with bushings and pads of Delrin or another inert plastic. Preventing direct contact between the
metals is the key to defeating corrosion. Below the waterline, an array of sacrificial zinc anodes will prevent galvanic corrosion; their service
life is predictable, and replacing them becomes a part of regular maintenance. Owners especially concerned about galvanic corrosion can specify
an on-board metering system that constantly measures corrosion potential. Checking the meter daily will immediately warn the crew of unusual
circumstances underwater. However, most aluminum boats enjoy a corrosion-free life after decades of service, protected only by zinc anodes.
The earliest modern aluminum hulls, built right after World War II, were riveted. When thin plating is required to meet strict weight
requirements (as aboard Palmer Johnson's 50-knot, 100-foot motor-yacht FORTUNA, built in 1979 for King Juan Carlos II of Spain) rivets are still
often the answer. There are 100,000 rivets in FORTUNA's superstructure, all hidden by painstaking filling and a mirror-smooth paint finish. Her
hull is welded, though, for most applications the preferred method of joining aluminum plate.
A proper weld in aluminum is at least as strong as the metal it joins, so an aluminum yacht, including frames, stringers, gussets, bulkheads,
deck, and all the other zillion pieces, becomes essentially a one-piece structure. Welds comprise only about 3% of the structure. The other 97%
is plating, framing, etc. that's manufactured at the mill under strict control. Both the American Bureau of Shipping and Lloyd's insist on
independent analysis of the alloy to ensure its metal content, test its strength, measure elongation under strain, and so forth. Palmer Johnson
does that routinely, checking a "coupon" of plate--engineering-ese for a small piece--for every 1,000 lbs or so of raw material. Most Palmer
Johnson yachts over 79' are intended for ABS classification; those that aren't are built to identical specs, but aren't surveyed during
construction by an ABS representative. ABS won't classify yachts 79' long or smaller, but Palmer Johnson builds them to classification standards.
Aluminum plate doesn't leak, doesn't soak up water, doesn't delaminate, doesn't deform under heat in normal service--it just sits there,
depending on the welds to keep it in the shape of a boat. Worried about a weld being less than perfect? They're easy to inspect whenever you
want, using ultrasound and X-rays. Palmer Johnson always spot-checks welds during construction, and ABS and Lloyd's require it. Their surveyor
decides where and how much to test. First-class boatbuilders like Palmer Johnson employ expert welders, certified ABS and/or the U.S. Navy.
Welding is a skilled craft, and learning to do it right, to develop the eye-hand coordination, to master the submerged-arc processes required for
joining aluminum, to lay down a weld that equals or exceeds the strength of the plate, takes time. Palmer Johnson figures on 1-1/2 to 3 years
before a man is skilled enough to pass certification, and he's not allowed to strike an arc on a critical component of a new yacht until he has.
Is this too much time to spend creating a productive employee? Not at Palmer Johnson. Once a part of the team, people tend to stay: Average
length of service for employees is currently 10+ years. It's not unusual to meet a 40-year-old foreman with 20 years' seniority--and he's way
down the list. For instance, the construction manager has been there for 35 years.
In catastrophic mishaps, a welded aluminum hull's ruggedness can pluck your yacht from the Total Loss category. Visit Palmer Johnson,
Incorporated, in Sturgeon Bay, Wisconsin, and they'll show you pictures of Yankee Girl, the great Sparkman & Stephens IOR racer built of aluminum
there in 1971. After a successful racing career, Yankee Girl fell victim to errant navigation and washed ashore on a rocky beach in southern New
England, coming to rest in a foot and a half of water and unfortunately drew nine feet. By the time she was dragged off three months later, a
large section of one side was nearly flattened from pounding against the rocks at every high tide. But she didn't leak. She was towed to a nearby
yard, the damage cut away, new frames welded in, and replated. She sailed away literally as good as new.
It's almost as straightforward to modify an existing aluminum yacht.
FORTUNA, for instance, started life as a 86-footer, until H.M. the King decided he needed more speed and a bigger cockpit. When you modify a
composite yacht, you depend on the adhesion between the new and old laminates to keep body and soul together. It's easy to make the changes look
good cosmetically, but will the glue hold? With aluminum, you inspect the welds--if the welds are good, the new structure is 100% as strong as
the old. No guesswork. Ditto for surveying an aluminum yacht before purchase: The surveyor can check everything visually, hire a lab to
spot-check welds and even audiogauge plate thickness, although aluminum plate, unlike rust-prone steel, rarely loses enough gauge to worry about.
Again, there's no guesswork, no "We think..." or "We hope...."
Except for cosmetic purposes, 5000-series alloys don't even have to be painted above the waterline. The unpainted metal reacts with air to form
aluminum oxide, a hard, protective, and, unfortunately, dull-grey coating that protects the underlying metal. Commercial aluminum workboats,
whose cosmetic appearance concerns no one, are often left unpainted above the waterline. Yachts are seldom so ill-treated. Palmer Johnson takes
advantage of modern paint systems to enclose the yacht in a durable, low-maintenance linear-polyurethane shell, and uses a schedule of primers,
fillers and polyurethanes manufactured by U.S. Paint, and offers a three-year paint warranty. One redcoat--prep and spray--during that period is
included in the price of the yacht.
Creating the shell is a multi-step, labor-intensive process demanding painstaking attention to even the smallest detail. First the finish
crew--it doesn't seem accurate to call them painters anymore--coat the abraded and cleaned aluminum with anti-corrosive primer. This etches the
metal and creates a tenacious base for subsequent applications. After sealing the anti-corrosive with a high-build epoxy primer, the crew fairs
the surface with a two-part filler. Here's where good building practice pays off: The less filler you need to create a perfect surface, the less
unnecessary weight you add and the few man-hours you spend. After more primer, and more filler if necessary, the surface gets a final spray of
epoxy primer, a thorough sanding, and the first coat of Awlgrip linear polyurethane topcoat. After about two weeks of drying time, the finishing
crew sand again, and spray on a final coat of Awlgrip. Palmer Johnson practice demands that the finish be mirror-smooth.
Below the waterline, there's less fairing and more attention to creating an impervious shell between metal and seawater, with four applications
of barrier-coat, followed by one of primer and then antifouling per the paint manufacturer's recommendations. Most experts endorse a
non-copper-based antifouling on an aluminum hull; however, some feel that copper-based paint can be used if the barrier coat is maintained, and
the yacht's crew inspects the bottom regularly for damage that exposes bare metal.
The finish process takes time: Figure eight months to prep a typical 150' yacht at Palmer Johnson, and a couple of weeks to topcoat. The actual
painting time might be as short as five hours, with five painters working simultaneously. Applying the paint is only 2% or so of the total job.
Finish painters tend to work odd hours (nights and weekends) to avoid interference from carpenters, joiners, and other dust-raising craftsmen.
Palmer Johnson employees are proud of their boats, too, and rightly so: They build the best custom boats in the world........and they do it with
aluminum.
Author's bio: Michael A. Smith is a Contributing Editor at both Yachting and Boating magazines. For 20 years he was a professional crewman and
captain on a variety of vessels, both pleasure and commercial, sail and power. Since 1986, he's specialized in writing on the technical aspects
of boating. He lives in Stamford, Connecticut.
