CONTAINMENT SPECIAL
CASE STUDIES
CASE STUDY - 11 MOVING TOGETHER
SITUATION: USING NET WEIGHTS
INCIDENT: DIFFERENTIAL MOVEMENT OF THE NET CAUSING TEAR
RESPONSE: CHANGED WEIGHTING SYSTEM
The situation: On the fi sh farm – as in life – we want people to move together. Going ‘against the fl ow’ doesn’t help in the team, and it certainly doesn’t help when our net weights don’t move in unison. In this example, one fi sh farmer had re- cently acquired a new site from a differ- ent company. This was an existing opera- tion and the workers continued to farm the existing equipment under their new owners. And, over time, the new company started to review work at the site and put in place measures to improve the op- erations.
The existing nets (100m circles) at the new site were weighted on alternate down ropes using heavy fi xed weights. The new company started to think that the net needed additional weights to help main- tain the net shape in the tidal fl ows. They put new weights on to the alternate down ropes that, to date, had not been weighted.
The new weights used were not as heavy as the existing ones. This was a delib- erate ploy to achieve the total desired weight to be deployed on each net.
The incident:
Unfortunately, however, the differ- ences in weights between the old and new weights caused a problem. Unknown to the farmer, the two weights moved dif- ferently in the tide – they were not in unison. This led to differential movement of the net and one part of the net became wrapped around the fi xed weight and caused it to chafe over time. This led to the
net tearing and the fi sh escaping. It should be noted that this fi sh farmer – like many – employs divers on a regular basis to check their nets at all their sites.
THE RESPONSE To help identify the cause of the problem, the company marked the position of the net on the circular pen unit. This was done so that when the net was taken ashore for in- spection, the company could easily know how it was aligned on the site – this simple action made it easier to speedily identify the cause. As soon as the company identified the cause of the problem, they changed the weighting system to prevent a similar incident occur- ring.
The examination of other nets at the site showed that chafe was beginning to occur elsewhere, although not to the same extent. The net in question was worst, since it was at the end of the site subject to the greatest tide.
As well as a weighting issue, this was also an inspection issue. Although the company had put in place expensive measures to help identify any net problems before they be- came an issue, they had not been picked up by the divers on this occasion.
So the company also put in place measures to ensure that their subcontract dive teams are all trained in the issues to look for when undertaking their inspection duties.
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