A new corer having a larger- diameter barrel of plastic was designed 

 to overcome some of the problems encountered with corers previously 

 used. This corer utilizes a barrel made of high-impact grade, polyvinyl 

 chloride (PVC), extruded plastic without an inner liner. The barrel 

 diameter is 3.50 inches outside and 3.22 inches inside. Barrels as much 

 as ten feet long have been used successfully in water as deep as 1,200 

 fathoms. Piston and gravity cores eight andninefeet long, respectively, 

 have been obtained. Tensile, compressional, and impact strengths 

 of PVC are, respectively, about one-tenth, one-third, and one-half 

 those of steel. PVC is light in weight (specific gravity of 1.35), easy 

 to cut into short lengths, and cheap enough (about 75 cents per foot) 

 to be expendable. This plastic appears to be nearly impervious to 

 moisture and, consequently, requires no additional sealing except at 

 the ends to insure interstitial water retention in the sediment core. 

 The use of this corer, named the Hydro plastic-barrel corer, is 

 recommended whenever engineering studies are to be performed on 

 sediment samples. (See Reference X-31.) 



c. Hydrostatic-type corer 



The hydrostatic, or vacuum, corer was developed by Petter son 

 and Kullenberg and later modified by Sysoyev andKudinov. The principal 

 difficulty with this type of corer is that while sediment is sucked into 

 the barrel at a relatively constant rate the corer penetrates the bottom 

 at a decreasing rate; consequently, distortion of the sediment results 

 from the discrepancy between the two rates. For this reason it is 

 not considered advisable for the Hydrographic Office to acquire a 

 hydrostatic corer, although it is capable of taking cores over 100 

 feet long under optimum conditions. (See References X-15, -28, and 

 -38.) 



C. CONTINUOUS- PROFILE SUBBOTTOM EQUIPMENT SYSTEMS 



Although thicknesses of bottom sediments were measured by echo 

 sounding twenty years ago, continuous-profile devices for obtaining 

 subbottom reflections are a relatively recent outgrowth of marine 

 seismic reflection techniques. Echo sounders and continuous -profile 

 equipment are similar and basically consist of: (1) a sound source 

 transducer, (2) one or more receiving transducers, (3) a pre- amplifier, 

 (4) a filter network, (5) a power amplifier, and (6) a recorder. Contin- 

 uous-profile equipment systems are characterized by a sound source 

 having a high repetition rate and filters to permit the selection of 

 high frequencies (usually greater than four kilocycles) for the resolu- 

 tion of thin-bedded strata or low frequencies (usually lower than 500 

 c.p.s.) for maximum penetration of the sediments. 



X-4 



