Research, development, production and evaluation of innovative grab sampling devices with a view to improving the quality and efficiency of sea-bed sediment sampling
- Reference:
- 08/P18
- Organisation:
- Gannet Scientific Services (with Plymouth Marine Laboratory and Cyclone Marine Ltd)
- Amount Funded:
- £43,600 (for Phase I only)
- Status:
- Complete
It is probable that a major factor in grab-sampling difficulties
lies in a design feature common to all current grab types. That is,
the closure of the grab jaws depends on the lifting tension of the
grab cable. This obviously limits the initial closing force on the
jaws to the weight of the grab, but also relies on a near vertical
angle of the cable for efficient sampling. Any significant sideways
pull will tend to pivot the grab and drastically affect sampling
efficiency.
There are a number of possible solutions in grab design that
might solve or alleviate this problem. Either the grab can be
designed so that a sideways pull by the cable is not as likely to
tilt or lift the grab as the jaws close, or alternatively, a
departure from conventional design can be made whereby the closure
of the jaws is independent of the cable. This project aims to
investigate both of these routes with a view to producing and
testing grab designs that will sample more efficiently, especially
in coarse or hard packed sediments and in difficult conditions.
Twin sampling versions will also be investigated.
Progress so far has resulted in the production of a prototype
cable-closed grab with a very low profile and an operating geometry
that aims to maximise sampling efficiency by minimising the effects
of cable side-pull. The design incorporates many innovative
features, including the use of a differential windlass in place of
lever arms. This grab is ready for field testing.
A design for the second prototype grab has been resolved. This
grab will use compressed air and a stainless steel ram to achieve
closure. The design includes several of the features of the cable
closed grab.
Twin-sampling versions of both types will be investigated
following field trials of the first prototypes.
Addendum Report
In July 2009, compatibility trials of the twin grab were
conducted as part of the East Coast REC survey work. A short
report on the findings of these trials is now available for
download (May 2010)
MEPF REC 08/04 - Addendum
Report