Ship-Shape Solutions - continued

Polyurethane Goes Sailing

by John Roderick, Mearthane Products Corp., Cranston, RI

Polyurethane is frequently selected for manufacturing a wide range of elastomeric components because the material is exceptionally versatile, and may be custom-formulated over a wide range of values to suit the requirements of specific applications. Marine product manufacturers take advantage of this versatility for components used above and below decks and even below the waterline.

Submarine dump valve seal

The dump valve on a submarine is used to discharge waste products that have accumulated aboard the vessel. A 10-in. diameter graphite-impregnated ball valve seal is a critical component that prevents sea water, at pressures up to 900 pounds per square inch, from entering the submarine by way of the valve. The high compression set of the polyurethane ensures that the component has sufficient memory to spring back to optimal sealing position in shallow waters where the pressure is off--even though the valve can be exposed to continuous high pressures for weeks on end as the submarine patrols in deep waters.

Polyurethane end stops for sheet travelers and winch gears.

An absolutely unique requirement of this seal is extreme shock resistance to energy waves produced by exploding depth charges outside the submarine's hull. All of the thermoplastic materials originally tested for this application proved to be too brittle, and cracked when subjected to repeated concussions of a simulated depth charge attack. The graphite-impregnated polyurethane (an elastomer) is self-lubricating and provides an optimal combination of hardness, tensile strength, elongation and flexibility to maintain a constant seal. Back on the surface, soft, durable and water repellent polyurethane makes an ideal seal or gasket for portholes and hatches (like a 60 Shore A bulkhead hatch used on U.S. Navy destroyers.)

Sailboat deck accessories

Polyurethane can be formulated for hardness, abrasive resistance and weatherability. For example, UV-resistant polyurethane is used in end stops for sheet travelers. These extruded aluminum parts allow lines attached to a track to follow the movement of the boom from one side of the yacht to another. The parts cost a little more than rubber, but resist continued exposure to sun and salt two to three times longer.

Self-lubricating wear parts

Because polyurethane has an extremely low coefficient of friction when wet, it can make exceptionally good self-lubricating wear parts below the waterline. A prototype, single-piece polyurethane cutlass bearing (used to support the propeller shaft where it exits the hull) demonstrates performance and rotational wear resistance better than conventional rubber bearing designs.

Polyurethane makes an ideal seal or gasket for portholes and hatches.

Not only is polyurethane extremely versatile, but after submission to a peroxide or sulfur curing process, urethane can also be machined with standard metal working equipment. This makes prototype part development and low-volume part manufacturing very economical.

For more information: Circle 524 - Mearthane Products Corp. or connect directly to their website via the Online Reader Service Program at http://www.OneRS.net/105df-524

Battery Isolator for Marine Applications

Solid-state switches by Cole Hersee Company, South Boston, MA, are ideal for boats using a standard battery to start the vessel and a second battery to run bilge pumps, winches, blowers and equipment. The battery isolators direct charging current into the battery with the lower charge, allowing the starting battery to properly provide a strong burst of energy to start the engine, while running the equipment off the second battery.

* Battery isolator switch

The electronic sealed units contain two diodes. Power supplied to the middle stud of the battery isolators flows to each of the other studs. As current can flow in only one direction, current cannot drain from one battery to the other, so each stays properly charged. They have long lives because they are solid state and protected against contaminants, can withstand vibration and temperature extremes, and are available in a range of amperages from 42A to 250A for systems of 12-36V DC.

For more information: Circle 527 - Cole Hersee Company or connect directly to their website via the Online Reader Service Program at http://www.OneRS.net/105df-527