Performance of the device
Bait run times and entanglements
Baits were trialled through the chute on the third trial on 09.10.97 while using the Arrow paravane.
The deck hose was connected to the trough and, with water flushing through the chute, baited snoods were deployed. Bait flushing times were three to four seconds. After 14 baits were fed through the chute, a hook-up occurred on the paravane wire resulting
in the abandonment of snood timings.
With so few baits trailed through the chute, this trial could not be considered comprehensive
All three paravanes worked at keeping the chute down in the water column. The Arrow and Flexi-wing were the most effective in terms of the angle of the chute and the setting depth (based on the number of metre marks visible above the water).
All trials of the 09.10.97 tests were made at towing speeds of 7 and 10 knots. At 10 knots all three paravanes appeared to be less effective with the chute riding higher in the vessels wake.The By-wing paravane was the least effective, with up to seven
of the eight marks visible above the water.
At 10 knots towing speed, both the Flexi-wing and Arrow paravanes (towed from the base of the chute on 5 and 6m wire strops), made a very audible vibration noise. The Skipper commented that this noise may deter the target species when surface longlining.
During the second set of trials, the vessel was travelling at a slower speed due to high seas, and the vibration noise experienced at higher speeds was not heard. After a few minutes towing, the tail came away from the Flexi-wing paravane.
All three paravanes used in the five trials were affected by the vessel's prop wash. The prop rotated clockwise with a pull from port to starboard, and the paravanes were pulled towards the starboard stern quarter. The angle of the USD appeared to vary
from 15 to 20 degrees to starboard. With the second set of trials, the length of wire strop was increased in an attempt to clear the paravane from the prop wash, however, the effect was the same.
Base plate and hinge operation
The base plate and hinge were effective and did not appear to place excessive force onto the stern transom plating. The chute was observed to flex and show signs of movement, but this appears to be from water resistance rather than force transmitted
from the paravanes.
No part of the base plate hinge or chute malfunctioned during the trials. On completion of the trip some obvious rust marks were starting to appear. It may be that a non-rusting material is required if the chute is to be used continuously.
Performance of the retrieval and deployment system
Difficulties were experienced with the deployment and retrieval system. When the chute was three quarters deployed, the trough was still protruding through the hole cut through the heli-deck. The downward pull of the paravane in the water jammed the
USD against the edge of the hole in the heli-deck, and it took up to three crew straining on ropes to clear the hole. This difficulty was compounded by the need to pass verbal instructions up to the crew managing the chute and hand winch from the heli-deck.
Once the chute was fully deployed and contained in the pivot arm with the retaining collar, the main locking pin had to be inserted to connect the chute to the pivot arm by aligning holes drilled into each component. This often required the repositioning
of the chute in the pivot arm by the winch person before the holes would align and the locking pin could be inserted.
During the second set of trials, in gale conditions, considerable bending occurred as the chute was retrieved. At the point where two thirds of the chute was out of the water, the paravane was still working against the crew hauling in, and with a swell
of two or more metres, the amount of curve the paravane end of the chute took up was considerable. No damage resulted from this action on the chute.
Given the very limited sea trails of the chute device during this trip, the device was still considered to be untested. However a number of modifications were recommended.
- The paravanes should be incorporated into the chute, making it a one-person operation, removing the dangers and difficulties associated with deployment and retrieval of the paravane and wire strop in large seas.
- Some form of cradle, guide or track could be developed to contain the chute during deployment/ retrieval operations, allowing for a one-person operation.
- The use of a hydraulic winch with hand control at the stern deck, to allow for a one-person operation, creating a smooth and simple deployment / retrieval of the chute.
- An even longer and stronger tube, to allow deeper bait delivery and clear the vessel's wake more effectively.
- The chute should be positioned away from the prop wash and the disturbance of the water column, therefore avoiding the prop wash effect while towing the deployed chute.
- The feed tray should be detachable during retrieval or deployment of the tube.
- A longer paravane tow strop could be used to enable the chute to be fully set before the paravane need be deployed, this would prevent any pressure or loading on the chute while only half deployed in the water. If this system was used, a way of
tripping the paravane would need to be found for the retrieval phase.