Hydraulic suction dredges 



By far the most promising device which has yet appeared for the control of 

 all stages of the life cycle of the drill is the hydraulic suction dredge. This was 

 first developed by the Flower brothers in the nineteen thirties (H. B Flower, 

 1938 ; 1948; J. R. Nelson, 1948a, 1948b) principally to remove drills and other 

 enemies from oyster beds. Since that time some 6 more suction dredges have been 

 constructed (Glancy, 1953). These include a number of interesting modifications 

 associated with the needs of the owners Because of the versatility of these dredges 

 and their usefulness in deeper water, they are utilized in a number of the operations 

 involved in oyster farming. J. R. Nelson (pers. com.) informs me that the F, Mans- 

 field & Sons Co. suction dredge,, the "Quinnipiac" is employed principally m drill 

 control, but because it is the most efficient means available it is also employed to 

 a great degree in handling oysters and shells and other materials encountered in 

 oyster farming. 



Glancy (1953X whose concern is shared by the writer, seriously questions, 

 however, whether in drill control the method of operation of the suction dredge has 

 always been based upon the soundest biological principles . Among the many pertin- 

 ent questions which he poses are the following: (1) In the interests of maximum 

 efficiency in drill control is it advisable to design suction dredges for a number of 

 oyster cultural operations? (2) Are intake nozzles designed to most efficiently 

 remove drills from grounds over which they operate? (3) Is the construction of the 

 dredge boat adapted to effectively retain small drills? (4) What minimum width of 

 strip should be cleaned around uninfested oyster grounds to prevent the migration 

 of drills frcm adjacent infested areas? (5) What is the most expedient means of dis- 

 posing of captured drills? (6) What is the effect of this kind of dredging on oyster 

 bottom and on the animals living there? As is indicated in this review only some of 

 these questions have received answers, and most of these are incomplete . 



It is worth noting that in actual practice, at least one company ; the Frank 

 M„ Flower & Sons Go ,, has achieved satisfactory control of drills on oyster 

 grounds by ingenious application of the company suction dredge the "Frank M. 

 Flower" (H B. Flower, 1948) As developed by H. B. Flower and currently 

 applied (H. B. Flower, pers com,) this method of control involves three separate 

 transplantations of drills; the following description and discussion of the method 

 will be based on the drill cleaning of a 50 acre piece of bottom: 



Step. 1. After marketable oysters are harvested, the ground is thoroughly 

 suction dredged and the material so obtained is passed onto a conveyer belt screen 

 with trapezoidal openings 13/8x1 3/4 inches. The finer components of this- 

 material (a total of 3, 750 cubic yards of sand, fine shell, drills, etc., in this in- 

 stance) are flushed through the screen, transported to the nearest soft muddy 



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