Sleds and dredges
Rock dredges and Sherman sleds are deployed from Investigator to collect biological samples, sediment and both large and small rocks from shallow reef zones down to the deepest parts of the ocean providing a greater understanding of the changing dynamics of the sea floor.
Unloading a dredge full of rocks from the seafloor.
Epibenthic biological sled “Sherman”
Sherman is an epibenthic sled designed to sample on any terrain, but particularly rough seamounts and reefs. The sled has a mouth area of 0.5m^2 (1 * 0.5m) and is constructed out of steel plate of 12mm thickness in the runners and 10mm in the box with specially designed cutting bars that collect large pieces of biota, and excellent rock samples at times. The samples are retained in a net of 30mm stretched mesh knotless nylon (2mm twine size) that it attached to the rear of the sled. This net is protected by a course external net and rubber matting on the lower side. The tow bridle system along with the solid construction allows Sherman to work in very demanding terrains. The bridle system uses lifting chain (high tensile tested chain) of 10 and 13mm thickness and tows from the back of the sled with the 13mm galvanised chain, secured to the runners, giving the angle of attack to the bottom. This bridle system allows for a 4 stage break-away system that has proven very reliable to date. The system is capable of having an in-faunal net mounted in the mouth area of 1mm mesh.
The rock dredge has an adjustable weak link (shear pin) system on the towing bridle (1-9 tonne). The mouth of the dredge was constructed from 12mm thick galvanised steel with a mouth area of 890mm x 305mm or 0.27m2. The chain bag consists of 6mm galvanised chain forming a square mesh with 70 mm sides. Attached at the end of the mesh bag is a plate to which the safety chain and two pipe dredges, each approximately 200mm in diameter and 500mm long, are attached. The chain bag is very resilient and collects larger invertebrates as well as rocks.
The rock dredge is attached to the trawl warp with a swivel of 5 tonne safe working load to minimise twisting and consequent damage to the warp.
The Smith-McIntyre grab is designed to collect a core of sediment approximately 320mm x 380mm x 200mm deep. The grab is loaded at the surface by compressing the springs and setting the jaws in the open position. The grab is automatically triggered upon landing. When triggered the grab is driven into the sediment by the preloaded springs and its own inertia. When retrieved, the jaws are forcibly closed by the retrieval cable collecting a relatively undisturbed core of sediment. The Smith-McIntyre grab is relatively reliable, returning a good volume of sediment from suitable bottom types.
Updated: 17 December 2014