Figure 6. — Gasoline-driven pump on the deck of a 

 clamming vessel. 



been increased from a few hundred gallons 

 per minute up to 3,500 gpm. One commercial 

 boat is now using two pumps to supply the 

 required amount of water. Hose size has been 

 increased from 21/2- up to Gi/j-inch inside di- 

 ameter with some boats doubling-up on the 

 smaller 6-inch hose. As the deck-mounted, 

 gasoline-driven pumps (Fig. 6) became inad- 

 equate, they were replaced with diesel-pow- 

 ered units installed below decks. This modi- 

 fication not only increased the available deck 

 space but also improved the operational safety 

 of the vessel. 



The dredge most generally used between the 

 late 1950's and the present has been a 40-inch 

 model (Fig. 7). This size dredge is particu- 

 larly suited to the handling and towing capa- 

 bilities of most of the commercial vessels in 

 the clam fleet. 



Although the size of this dredge is well 

 standardized, many minor modifications are 

 consistently being made in an attempt to im- 

 prove on its efficiency. These modifications 

 consist mainly of changes in the size and ar- 

 rangement of the water jets, variations in 

 placement and shape of the jet manifold, 

 changes in the volume and pressure of water 

 supplied to the jets, changes to the shape and 

 contour of the dredge knife, improvements in 

 the attachment of the knife to the dredge, 

 changes of the knife depth setting, variations 

 of towing speed, shape, and slope of the sled 



floor, construction and attachment of the chain 

 bag, and towing attachment between the dredge 

 and sled. During this period of development, 

 local modifications to the dredges reflected dif- 

 ferences in the characteristics of the areas in 

 which they were being used. The shape of 

 the dredge might be slightly different or the 

 type of jet header and arrangement of the jets 

 might be different; also, the type and shape 

 of the knife could vary from area to area. Be- 

 cause of these variations, the physical state of 

 the hydraulic jet dredge can be considered to 

 have been almost constantly changing (Fig. 8). 



EXPERIMENTAL GEAR 



As the commercial fishing effort increased 

 on the larger clam beds which were located 

 within easy distance from ports and processing 

 plants, these beds have sustained consistent and 

 heavy fishing jiressure. As the production rate 

 over these beds leveled out, rich beds located 

 at greater distances from ports and plants have 

 been used. However, the balance maintained 

 between the fishing time to be gained or lost 

 by traveling shorter and longer distances, vs. 

 the production rate(s) of the various fishing 

 grounds, became an important consideration. 

 It now appears that in order to maintain the 

 desired production level, either faster boats or 

 more efficient fishing gear is needed. The lat- 

 ter proposal seems to be the more practical 

 solution. One approach to updating or other- 

 wise improving the gear and fishing method 

 is to adopt methods and gear used by other 

 marine industries for use in the surf clam 

 industry. 



Early in 1963, a member of the surf clam 

 industry became interested in the development 

 of an airlift system based upon the principle 

 now used for collecting diamonds off the south- 

 ern coast of Africa. The principle involved is 

 that of pumping air down to the dredge where 

 the air is directed into the bottom of a large 

 hose extending from the dredge to the boat 

 deck. The air causes the mixed water-air col- 

 umn within the tube to become lighter than 

 the outside water and generates an upward 

 movement of the water within the hose. The 

 water flowing into the bottom of the hose to 

 replace the water which has moved upward 



