On several trials problems occurred where the snood was pulled out of the setting tube before the baited hook had left the base of the tube. The use of brushes at the top of the tube has overcome this problem.
The major design requirement for the trough was to ensure adequate and even flushing of the water over the trough surface and the smooth passage of water to the mouth of the setting tube. The devices with multiple water outlets at the top of the trough
provided adequate flushing.
The basic hinge assembly with the use of shock absorbers performed effectively on all trials.
Although problems occurred in moving the tube into and out of the setting position during the F. V. Daniel Solander and F. V. Brenda Kay trials, improved roller carriage design used on the F. V. Atu S second trial has over come
this problem. For the larger 50 metre vessels a hydraulic lift may be necessary because of the increased length and weight of the USD.
Setting Angle devices
When paravanes were trialled in the open sea by tuna fishing vessels significant problems occurred. The commercial trials identified three drawbacks in using the paravanes.
1. The paravanes made setting the USD difficult in rough seas. Once the paravane was in the water it created a strong downward force making retrieval of the device from the water a slow and arduous process.. Setting tubes fitted with paravanes were
also difficult to deploy and retrieve, particularly in adverse conditions.
2. Larger vessels with vastly greater prop wash turbulence experienced problems with two of the paravane types being unable to hold the minimum setting angle required. Although the Arrowhead paravane had the smallest surface area of any of the paravanes
trialled it was by far the most powerful and the only one that achieved a correct setting angle when trialled from the F.V. Daniel Solander in the Southern ocean.
3. During the setting process, hooks and snoods were occasionally caught in the paravane, causing delays in the longline setting operation while the USD was retrieved and hooks/snoods removed. Potential causes of the problem were considered ranging
from operator error to a back wash phenomenon behind the vessel.
The shock absorber method of angle setting has successfully operated in rough seas over several trips on a 30 metre tuna vessel. The use of a Forsheda mooring compensator may be appropriate for smaller (10 - 15 metre) vessels. Larger vessels will require
a spring shock absorber.(see figs 20 and 23).
An alternative to the shock absorber method may be to add weight the tube to set the angle of the setting tube. Weights could be added or subtracted from the tube to adjust for varying setting speeds and propeller wash conditions (see Figure 24 E)
Recovery and deployment devices
The optimal angle for deploying and retrieving the USD is the angle of set when the device is fishing (40 to 50 degrees). Because of vessel configurations, none of the trials were able to deploy and retrieve at this angle. The vertical deployment and
recovery device (as used on the first ATU S trial) was the least effective method, and potentially the most hazardous if the USD (when vertical) had broken loose from the mounting in a rough sea.
The need for up to five crew to deploy and retrieve the device (as occurred on the F. V. Daniel Solander) trial can be overcome by the use of a modified carriage system (see Figure 24), and a hydraulic retrieval and deployment device. For vessels
up to 30 metres length a simple block and tackle pulley system would be sufficient to deploy and retrieve the setting tube.
The early commercial trials identified a number of safety issues related to the operation of the USD device. Modifications made for the F.V. Atu S second trial ensured adequate safety of the crew during the deployment, retrieval and fishing stages.
These modifications included removing the paravanes, reducing the friction of the setting tube on the carriage system, changes in the securing system for the device when not in use, and changing the deployment and recovery system so that crew did not have
to lean out over the stern of the vessel.
This work was commissioned by the Department of Conservation through the Conservation Services Levy funded by the New Zealand fishing industry.
We would like to acknowledge the assistance of Department of Conservation staff (in particular Janice Molloy and Ian West).
Valuable assistance was also provided by Harry Verney (skipper of the M. V. Frae), Mike and Soo Wells (owners of the F.V . Kariqa), Jeff Moffat (Skipper of the F.V. Atu S), Tony Irvine (Managing Director , Moana Pacific Engineering
for providing engineering assistance and the design of the spring shock absorber), Brent Marshall, (Northern Fleet Manager, Moana Pacific Fisheries), Professor Manly (advice on chi squared statistic). Carl Fry, (Skipper of the F. V. Daniel Solander),
Scott Roger, First Mate, and crew. Paul Brewer, (Skipper of the F.V.Brenda Kay), Kent Peters, (General Manager,Tobe International )
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