pick up another boat
The practice of dry-stacking has become increasingly popular for larger craft, leading to the need for ever-larger lifts.
By Henry Baumgartner, Assistant Editor
Making those lifts is getting tougher all the
time. Especially if the job is shuffling expensive 10- and 20-ton motorboats
in and out of the water.
Forklifts, those old standbys for picking up pallet-size loads, are getting
bigger and stronger in order to haul the boats around. Marinas use the
increasingly powerful versions of the machines to lift boats out of the
water and place them gently on shelves in storage sheds, where the craft
are stacked as many as five layers deep. Companies such as the Wiggins
Lift Co. of Oxnard, Calif., and Taylor Machine Works Inc. of Louisville,
Miss., are supplying boatyards with monster forklifts, some of which are
capable of raising loads that can range from 20,000 to upward of 40,000
pounds at an 8-foot load center.
Previously, marinas had relied on gantry cranes to lift large boats, according
to Bruce Farber, director of engineering at Wiggins Lift. But over the
last 10 or 15 years, many marinas have adopted the practice of dry-stacking
boats that are not immediately required by their owners. This involves
pulling the boats out of the water and stacking them in huge barns for
storage. Moving a large boat might take an hour using a crane, and since
large marinas that dry-stack their boats may have to move dozens of them
in a day, there is an obvious advantage in using a forklift that can get
the job done in as little as three or four minutes.
Marinas
are turning to powerful forklift trucks to pull boats out of the water
for storage.
Dry-stacking was originally seen as appropriate for smaller boats, but
as the popularity of the practice has grown, larger and larger boats are
being stacked. The company has sold lifts to marinas across the United
States as well as in Australia, Brazil, England, Italy, Malaysia, and
Portugal, Farber said. Not only is it cheaper to store the boats in the
sheds than to have them take up valuable dock space as they sit idle for
months, it's better for the boats, which require less maintenance if they
are indoors under cover and get to dry out from time to time. The boats
are out of the weather and out of the sun. Hull-cleaning costs are lower.
Even more important, Farber noted, is an environmental concern. The U.S.
Environmental Protection Agency is increasingly worried about fuel spilling
from tanks and poisonous chemicals leaching from the anti-fouling paints
used on hulls and has been putting pressure on marina operators to do
something about these problems. Keeping the boats in dry storage when
they are not in use reduces not only the opportunity for fuel spills,
but also the time that water is exposed to chemicals.
"Up until four or five years ago, the highest-capacity machines we
had available could handle on the order of 18,000 or 20,000 lbs. at an
8-foot load center," or enough to pick up a 30- or 32-foot boat,
Farber said. By about three years ago, capacities had moved up to 27,000
to 30,000 lbs. at an 8-foot load center.
The load center is the point on the lower surface of the load directly
beneath its center of gravity. As this point moves away from the forklift's
mast—the upright track for the carriage that holds the forks—less
leverage is exerted on the load. Consequently, more power is required
to lift it, and heavier counterweights are necessary to keep the whole
operation from tumbling head over heels into the drink. Typical forklifts
in a warehouse operate at something like a 2-foot load center and are
designed to lift perhaps 2,000 or 3,000 lbs.; the length of the forks
would typically be about twice the load-center value.
There are other configurations of forklifts that handle massive loads.
Freight handlers use something similar to move shipping containers, but
in place of forks that slide under the load, these machines grasp it from
above. And "yard bull" forklifts exist that can lift as much
as 100,000 lbs., but the load centers are typically 24, 36, or perhaps
48 inches, so the moment is not as great.
Wiggins Lift pushed the capacity of its trucks to fill a 1999 order from
the new Gulf Harbor Marina in Nokomis, Fla., which needed a lift that
could handle a new class of boats that had never been dry-stacked before.
The Sea Ray 370 Express Cruiser and similar craft are heavy boats with
engines amidships. They were beyond the capacity of existing lifts. Since
the engines are usually the heaviest things on the boat, having them located
amidships tends to push the load center farther out, thus requiring more
power, pound for pound, to lift. Although the boat weighed in at 23,000
lbs. or so, since the center of gravity was 16 or 18 feet out, the load
was equivalent to 37,000 lbs. at an 8-foot load center.
Marinas
are using forklifts like this one to stack increasingly large boats as
many as five deep in large warehouse-like sheds.
"Gulf Harbor was the first time we took a big jump in capacity,"
said Farber. "We had to design a new mast, forks, and carriage."
The carriage holds both forks and travels up and down the mast. "For
lesser loads, if the mast is strong enough, it's stiff enough," Farber
said. However, he added that larger stresses can cause too much deflection
at the tip, causing stiffness to be more of a concern. This was dealt
with through the use of a truss.
"The main beam is a piece of rectangular tubing, rather than channel
or I-beam, and provides additional torsional stability," he said.
"There is also additional smaller tubing behind the mast." Also,
because of the increased load on the bearings associated with the mast
and carriage, now about 5 million inch-pounds, the size of the bearings
had to be increased.
The year after, the company was asked to design a lift to handle an even
bigger boat. It was designed, built, and delivered in five months, in
time for Christmas 2000.
Trucks in this class have capacities ranging from 26,000 to 33,000 lbs.
at a 16-ft. load center, which translates into 52,000 lbs. at 8 feet.
"We designed a whole new chassis and rear axle," Farber said.
The rear axle, which is used to steer the truck, had to be redesigned
to carry the massive counterweight needed to balance the nearly 50,000
lbs. of mast, plus the weight of the load. Farber estimated the total
weight on the rear axle at about 60,000 lbs. Meanwhile, it was also necessary
to give this behemoth as tight a turning radius as possible, since there
is often not much room to maneuver in the relatively confined spaces of
the boat storage sheds. The truck can turn at an 87-degree angle and has
a total turning radius of 220 inches.
No Lubrication Required
For the pin at the top of the axle that pivots horizontally, composite
bushings were used that don't require grease, since it would never be
possible to administer a lubricant. With 50,000 to 60,000 lbs. resting
on the pin, it would not be easy to force in grease. Farber estimated
that it would require a pressure of 6,000 to 10,000 psi. Given the weight
of the truck, jacking it up isn't an option.
The entire chassis had to be redesigned, also, to accommodate tires 6
feet in diameter. The forks had to be specially fabricated; they were
tapered and made of T1 A514 steel, rated for yield stress at 100,000 psi.
"They have to be as light as possible," noted Farber.
The design of these monsters was accomplished using Pro/Engineer CAD and
Pro/Mechanica finite element analysis programs from PTC of Needham, Mass.,
and the Cosmos/Works FEA program from Structural Research and Analysis
Corp., a Dassault Systemes subsidiary headquartered in Los Angeles.
Farber explained that the designers built the geometry in Pro/Engineer
as solid models. They took the geometry for the major structures, such
as the mast or the carriage, and analyzed them as single weldments with
Pro/Mechanica. The Cosmos program was used in less complex computing areas
where speed was more important, such as smaller or more localized structures
like pins, rollers, or brackets.
To validate the FEA work, during the load testing of the completed machine
engineers checked the deflections on the larger structures and they were
as predicted. What's more, added Farber, "The biggest machine has
been in service about one year now, and there have been no problems."
Is anything even larger in the works? "The next step is 60- to 70-foot
lift heights," Farber replied. "Only people's imaginations are
limiting us."