In this study, we explored the options of deploying devices designed to log
odontocete echolocation clicks (C-PODs) in a prospective tidal-stream
energy site off the west of Scotland. Our design needed to be deployable
from a chartered research yacht; the gear be light enough to be manually
handled by two people with a small capstan and that the mooring maintain
the submerged POD orientated vertically even in tidal streams.
1by Jim Elliott ([email protected])
PRIMaRE Annual Conference Wednesday 6th April 2011
Mooring scientific recording equipment in marine habitats is ordinarily
challenging.
But securing recorders in sites suitable for the extraction of marine
renewable energy is more so because a) The inherent energy of the site
substantially increases the risk of the equipment being moved or broken b)
The incumbent water motion makes it particularly hard to maintain correct
equipment orientation and c) fouling, sand blasting and scour are
particularly prevalent .
The specific difficulties differ between wave and tidal-stream energy sites
but the lack of experience in these sites and associated absence of fully
tested “best practise” is common to both.
2by Jim Elliott ([email protected])
PRIMaRE Annual Conference Wednesday 6th April 2011
The channel at the centre top of the image is Kyle Rhea between Skye (left) and
Glenelg (right)
POD #664 was moored in a sheltered eddy with the greatest effect of tidal flow.
POD #667 was moored in a couple of locations in a secondary context.
POD #666 was further to the south and thus less likely to experience the tide.
3by Jim Elliott ([email protected])
PRIMaRE Annual Conference Wednesday 6th April 2011
Silurian is run by the Hebridean Whale and Dolphin Trust and is used for marine
wildlife research and volunteer trips.
4by Jim Elliott ([email protected])
PRIMaRE Annual Conference Wednesday 6th April 2011
We designed two moorings based on the popular ‘J’ design. The difficulty
of tidal effect on buoyed lines from bottom to surface meant an individual
weight system for the C-PODs was required. C-PODs have 0.7kgs of
inherent buoyancy so a riser line (3 m of 10 mm Seasteel) was weighed by
25 kg of 6 mm long link chain and buoyed by a solid 5 kg float. A ground
line (16 mm Seasteel) equal to the depth connected this to the main weight
(concrete and chain filled tyre weighing 50 kg). This was then attached to
the surface (via 12 mm Seasteel) by a polyform ‘40’ inflated buoy and two
metre pickup buoy. Key to the deployment was the positioning of the
equipment relative to the tidal-stream. C-PODs have a detection range of
approximately 200 metres for porpoise. With the mouth of the site (Kyle
Rhea) being less than 150 m wide, the topography of the shore favoured a
relatively sheltered location close to the southern channel. As a
comparison, a second mooring was laid 15 km to the SSE in a low energy
site.
5by Jim Elliott ([email protected])
PRIMaRE Annual Conference Wednesday 6th April 2011
Images of the deck, POD, main weights and surface buoys.
6by Jim Elliott ([email protected])
PRIMaRE Annual Conference Wednesday 6th April 2011
7by Jim Elliott ([email protected])
PRIMaRE Annual Conference Wednesday 6th April 2011
The peaks show the influence from the tide as the POD is knocked down.
8by Jim Elliott ([email protected])
PRIMaRE Annual Conference Wednesday 6th April 2011
This POD was moved from various areas which show a change in influence by
the tide.
9by Jim Elliott ([email protected])
PRIMaRE Annual Conference Wednesday 6th April 2011
10by Jim Elliott ([email protected])
PRIMaRE Annual Conference Wednesday 6th April 2011
11by Jim Elliott ([email protected])
PRIMaRE Annual Conference Wednesday 6th April 2011
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