Ship-Shape Solutions

by Kimberly Chapple

Whether redesigning the entire boat-building industry, searching for a solution to a hostile underwater motion control application, or looking for a seal that exhibits extreme shock resistance to energy waves produced by exploding depth charges outside a submarine's hull--if you're working on a marine application, chances are you face significant challenges inherent in above- and below-surface design.

Changing the Way Boats Are Built

Virtual Engineered Composites (VEC) is a breakthrough technology being used by one boat manufacturer to radically change the boat-building industry. This fiberglass molding process uses a computer-controlled, closed-mold process that forces more styrene to bond with the composite, rather than escaping into the air. Boats are manufactured four times faster using VEC than traditional methods. Besides producing a tougher boat, this process surpasses EPA emissions standards, substantially improving the environment both inside and outside the manufacturing facility.

Manufacturing facilities are digitally connected to a VEC Solutions Center.

In the boat-building industry, VEC technology is primarily used for producing hulls, but will be used for other fiberglass parts as well, including decking, stringers and small components. The process has been compared to the manufacturing revolution not unlike the introduction of the assembly line by Henry Ford. Genmar Holdings, Inc., Minneapolis, MN, recently acquired the technology from VEC Technology, Inc., Greenville, PA, and is using it on its recreational boats line, beginning with its 17- to 21-ft. Larson and Glastron boat models.

Production takes place in a clean, automated and self-contained cell. A 2-part "floating mold," supported by water pressure in a surrounding vessel, takes the place of complex steel-and-wood support and open molds used in the past. VEC "mold skins," the liners that vary relative to the parts being made, can be changed in about an hour, making it possible to produce a number of differently sized and shaped parts in the same VEC cell.

The process begins with a spray of gelcoat on the mold skin by workers. Then precut pieces of proprietary fiberglass material along with precision-molded urethane foam sections are laid into the mold sections. The two mold halves are then joined together and a precise mixture of resin and catalyst are injected, under pressure, into the space between the mold halves. Water surrounding the mold supports it against this pressure and controls the temperature of the molded parts as it cures.

Boats are built four times faster using VEC technology.

Sensors inside the mold monitor every facet of the process and transmit data to a computer which controls more than 500 variables, including temperature, viscosity, flow rates, mass density, gel times and peak exotherms. It automatically adjusts the components to produce a fiberglass part cured in consistently optimal conditions.

Every VEC cell is also linked to a central computer at the VEC Solutions Center in Greenville for quality control and trouble-shooting purposes. The system is so precise, tests have shown less than one-pound fluctuation in total hull weight among the 1,000 hulls already manufactured.

During the process, the hulls incorporate a stringer system and boat floor in a single part, with backing plates in place for mounting the engine and other hardware. A 5-axis robotic router/driller precisely trims (to 1/1000th-in.) the hull and deck, cuts openings for engine and drive mountings, and locates holes for mounting hardware. Hull and deck parts then proceed separately down an automated production line for final assembly before being moved to a staging area for shipping.

For more information: Circle 521 - Genmar or connect directly to their website via the Online Reader Service Program at http://www.OneRS.net/105df-521

Circle 525 - VEC Technology, Inc. or connect directly to http://www.OneRS.net/105df-525

Mapping the North Atlantic

Like few other hostile environments for industrial components, the deep sea is a forbidding place to launch a motion control application. Frigid waters, the corrosive effects of sea water and extremely high pressures combine to create an environment where off-the-shelf components will fail--quickly.

The Bedford Institute of Technology, Newfoundland, Canada, had a research application that required them to map sections of the ocean floor in the north Atlantic. The institute was constructing mapping equipment that would have a cable attached to computer equipment on board the ship.

Rubber Duck stepper motor

The cable would house an array of sensors to be used to perform the necessary mapping work. It would be paid out behind a moving ship. The sensor array would settle to a depth of approximately 2500 ft. To prevent damage to the array during deployment, the cable is closed until in place. A motor would be attached at the end of a long cable and would open the sensor array for data collection once it settled into position.

Challenges included preventing water from entering the motor and the electrical cables, as well as using construction materials that were corrosion resistant. Allowances for material shrinkage needed to be made, as O-rings and other elastomeric materials easily compress under oceanic pressures. Additionally, power losses that occur over the 1,000+ ft. umbilical cord from the ship had to be accounted for, and a filling oil whose thermal properties assure it is still a liquid at high pressures and low temperatures had to be used.

After making some calculations, it was decided that a U42 two stack, frame 42 stepper motor would be the optimum unit for the job. The challenge was to construct such a motor to survive and reliably operate when submerged in ice cold sea water. Empire Magnetics, Rohnert Park, CA, took on the challenge of motor design and fabrication, while Bedford took on the task of testing the motors, with the understanding that some iteration would be required to get the job done properly.

Empire began work on 316 stainless steel housings, O-ring seals, waterproof cables, oil filling and pressure compensation. Bedford built up a pressure chamber from a section of a ship cannon that could withstand pressure to 5000 psi. Then the testing began.

Initial results were very positive. The motor was working as expected at slow speeds, but it was not operating at high speeds and at the highest pressures.

After some additional testing, it was discovered that the ball bearings in the front of the motor had been supplied with metal shields. The pressure on the seals was so great that this shield had been perfectly formed to the shape of the balls in the bearings, so much so that to the eye it was difficult, even upon close inspection, to discern what was happening.

It turned out the first seal set up was actually two seals on a common shaft. The basic problem was the space between the two seals. As the pressure increased on both the inside and the outside, the seals moved. Since the inner seal was against the bearing, it formed the bearing shield metal around the balls in the bearing. The cure was to arrange for pressure equalization between the two seals, while maintaining the seal integrity. Once everything is at equal pressure, only the compression of the material itself needs attention.

The fact that the friction of the metal shield against the ball increased with speed and pressure explained the symptoms Bedford had observed. A quick modification to the motor eliminated the shield and the pressure differential that deformed the shield, and the motor was back in the test tank in short time.

The Bedford Institute went on to build the mapping equipment utilizing the deep sea motors from Empire Magnetics. While the system has been in operation and running smoothly for more than five years, Empire continues to design motors for deep sea and marine applications built to customer specifications.

For more information: Circle 522 - Empire Magnetics or connect directly to their website via the Online Reader Service Program at http://www.OneRS.net/105df-522

Circle 523 - Bedford Institute of Technology or connect directly to http://www.OneRS.net/105df-523

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