Petrel of South Africa is offering a new deck system for tuna lifting which it says is faster and more efficient than the conventional boom mounted power block.
It says the system means vessels can shoot the nets more often, because hauling in is much faster and easier. Also, since it is now more common to throw nets around smaller schools of tuna, this means that the catch rates have gone up significantly and trips have become more economical, Petrel adds.
The system is made up as follows: a hydraulically-driven net winch. This is a similar concept to the power block conpect, which it is a Vee Sheave . But it has a number of advantages. Since it is mounted just above the ship's rail, pulling pressure is exerted from much lower down than would be the case for a power block. This means the vessel is far more stable and is able to fish in rougher seas.
Secondly, the net winch can be adjusted for slew and tilt and this gives the operator better control when bringing the net in as he can compensate for any twist in the net. The net is led over the net winch and under a jockey drum. This gives a good wrap angle over the net winch and thus ensuring good traction and high pull.
The other element is a net crane stacker. The net is led up from the jockey drum to the net crane stacker for stacking in the net bin. Once again, the net crane again allows the operator to eliminate twist by manipulating the roller head on the crane. Because the stacking operation is now independent of the hauling-in operation, the crane can be positioned to allow efficient packing of the net in the bin without having to be worried at the same time hauling in the net. In addition, the net crane is fitted with a seven-tonne winch for lifting heavy equipment on the aft of the ship.
Main pursing winches
The Petrel winch system is made up of a main purse winch with a large capacity drive and multi-motor hydraulic drive system. This allows great flexibility in both speed and pull. The winch has a hydraulic calliper brake which reduces the tendency to bind as found with band brakes. A double reduction on the cable spooling gear allows fine adjustment to provide perfect spooling.
The second winch has two drums, mounted and clutched on the same shaft. The larger drum carries the other end of the purse wire and the smaller drum is used for the end wire. The drive is transferred by using clutches from one drum to the other.
Both winches are fitted with warping heads and horns to improve their versatility on the deck.
