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Clam shake.

Clam Shake

Clam harvesters and their equipment must work daily in a harsh sea environment. The large, heavy loads of clams require rugged equipment, while seawater constantly threatens to corrode metal parts. A custom-made shaker screen manufactured by Simplicity Engineering (Durand, Mich.) has helped the Borden Clam Products Co. (Cape May, N.J.) contend with its clam harvest for over a year.

Weather permitting, Borden's clam boats harvest surf and quahog clams year-round off the southern coast of New Jersey. Of the company's seven boats, three are outfitted with Simplicity shaker screens. After locating the clam beds, the crew dredges up the catch and uses the screen to separate the marketable clams from other sea life and debris.

Borden had used a shaker screen, made by its own welders, that was equipped with a hydraulic-driven, eccentric motor, according to Borden boat operations manager Gene Janowski. The continual maintenance required by this model, however, forced Borden to approach the A.K. Robbins Co. (Baltimore, Md.), a Simplicity Engineering distributor. For over 50 years, Simplicity has manufactured screens, similar to the clam shaker screen, for aggregate and mining applications.

Based on existing screen models, Simplicity fabricated a new clamming screen primarily by adding inverted, stainless-steel angles. The screen features a four-bearing drive with positive displacement. Since durability is a requirement in clamming equipment, bearings and shaft were integrated for sturdy assembly and long life. Rugged H-beams were tied with strong channels to form a rigied main frame, and stainless-steel components provided corrosion protection against the onslaught of salt water and sand. Heavy-gage side plates were reinforced by full-height corner support brackets. Radial drilling in the side plates allowed any necessary adjustment in the field. The screen was originally powered by a 5-hp hydraulic motor, which has since been replaced with a 5-hp electric motor mounted to the main frame.

The device, which has been operating without significant maintenance problems, is usually loaded to the maximum depth of about four inches. A typical load for the screen is about 3200 to 3600 pounds - the weight of one cageful of clams. According to Borden, the screen's maximum loading has not yet been determined.

On the Misty Dawn, the first boat to be outfitted with a Simplicity screen, the crew of four begins its daily outing by using a sophisticated electronic depth finder to locate clam beds. Generally, suft clams (Spisula solidissima) are found relatively close to shore, in waters from 20 to 60 feet deep, while quahog clams (Mercenaria mercenaria) are usually about 40 to 60 miles out, in waters from 140 to 200 feet deep. Federal and state conservation regulations impose strict limitations on both the times for harvesting surf clams and the maximum amount that can be caught. A harvest of quahog clams, which are subject to fewer restrictions, can reach 1600 bushels per 24-hour excursion. (A bushel is roughly equivalent to 35.2 liters.)

After locating the clam bed, the crew deploys its dredging equipment. The vessel makes a sweep of the area, pulling the dredge across the ocean bottom. The working end of the dredge, the knife, cuts into the bottom, scooping up clams as it goes. After each sweep, the dredge is raised and emptied into a large hopper. The catch is then funneled onto the shaker screen.

The Misty Dawn's single-deck screen, which has a surface area of 5 by 8 feet (the two other boats equipped with shaker screens have later models, each measuring 3 by 6 feet), vibrates to return sand, half shells, undersize clams, undesirable sea life, and seaweed through the deck and back into the ocean. The screen deck consists of five sections of staggered and stepped stainless-steel angles that let unwanted material fall through 1 1/8-inch openings. Clamming regulations require that a surf clam measure at least 5 inches edge-to-edge to be kept. Some surf clams are as big as 12 inches; quahog clams, which have no size restrictions, are generaally 2.5 to 5 inches.

The marketable clams slide off the shaker screen at a 15-degree decline and onto a conveyor belt that runs down the center of the vessel's hold. Tall wire baskets, three across on both sides of the conveyor, collect the clams to facilitate unloading at the dock. As the clams move down the conveyor, a crew member positions a metal chute above a basket and opens a door on the conveyor's side rail. The door directs the clams down the chute and into the basket.

The entire dredging and separating cycle is repeated about once every 20 minutes, or three times an hour. The shaker screen, after loading, requires approximately two to five minutes per cageful - or about 32 bushels - of clams.
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Title Annotation:clam harvesting
Author:Kim, Irene
Publication:Mechanical Engineering-CIME
Article Type:column
Date:Aug 1, 1990
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