Jim Elliot Presentation

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.



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.



Silurian is run by the Hebridean Whale and Dolphin Trust and is used for marine

wildlife research and volunteer trips.



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.



Images of the deck, POD, main weights and surface buoys.



The peaks show the influence from the tide as the POD is knocked down.



This POD was moved from various areas which show a change in influence by

the tide.



Jim Elliot Presentation

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