Sleds and dredges

Dredges, sleds and grabs can be deployed from RV Investigator to collect biological samples, sediment and rocks from the sea floor.

What they're used for

Sherman sled

 ©Asher Flatt

The Sherman sled is a robust epibenthic sled designed to sample on any terrain, but particularly rough seamounts and reefs.

Rock dredges

The rock dredge is used to collect rocks from the seafloor.

Smith-McIntyre Grab

The Smith-McIntyre grab is designed to collect a core of sediment approximately 320 mm x 380 mm x 200 mm deep.

How they work


The sled has a mouth area of 0.5 m2 (1 * 0.5 m) and is constructed out of steel plate. It has with specially designed cutting bars that is capable of collecting large pieces of biota, and rock samples. Samples are retained in a net of 30 mm stretched mesh knotless nylon (2 mm twine size) that is 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 13 mm thickness and tows from the back of the sled with the 13 mm 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 1 mm mesh.

Rock dredges

The rock dredge has a chain-link bag with large metal-jawed opening that scoops the contents into the bag.

The mouth of the dredge is constructed from 12 mm thick galvanised steel with a mouth area of 890 mm x 305 mm or 0.27 m2. The chain bag consists of 6 mm 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 200 mm in diameter and 500 mm long, are attached. The chain bag is very resilient.

Smith-McIntyre Grab

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. During retrieval, 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.