The Puretic power block is a special kind of mechanised winch

Winch

A winch is a mechanical device that is used to pull in or let out or otherwise adjust the "tension" of a rope or wire rope . In its simplest form it consists of a spool and attached hand crank. In larger forms, winches stand at the heart of machines as diverse as tow trucks, steam shovels and...

 used to haul nets on fishing vessel

Fishing vessel

A fishing vessel is a boat or ship used to catch fish in the sea, or on a lake or river. Many different kinds of vessels are used in commercial, artisanal and recreational fishing....

s. The power block is a large powered aluminium pulley

Pulley

A pulley, also called a sheave or a drum, is a mechanism composed of a wheel on an axle or shaft that may have a groove between two flanges around its circumference. A rope, cable, belt, or chain usually runs over the wheel and inside the groove, if present...

 with a hard rubber-coated sheave

Sheave (mechanical)

A sheave is a wheel or roller with a groove along its edge for holding a belt, rope or cable. When hung between two supports and equipped with a belt, rope or cable, one or more sheaves make up a pulley. The words sheave and pulley are sometimes used interchangeably.A sheave can also refer to a...

. While many men were needed for the back-breaking work of hauling a purse seine manually, the same work could be done by fewer men with a power block.

The Puretic power block revolutionized the technology of hauling fishing nets, particularly purse seine nets. According to the Food and Agriculture Organization of the United Nations (FAO)

Fão

Fão is a town in Esposende Municipality in Portugal....

, "no single invention has contributed more to the success of purse seine net hauling" than the power bloc, which was "the linch-pin in the mechanization of purse seining".

History

The power block was invented by a Croatian

Croats

Croats are a South Slavic ethnic group mostly living in Croatia, Bosnia and Herzegovina and nearby countries. There are around 4 million Croats living inside Croatia and up to 4.5 million throughout the rest of the world. Responding to political, social and economic pressure, many Croats have...

 fisherman, Mario Puratić

Mario Puratić

Mario Puratić is a Croatian-born American inventor who made major advances in fishing technology, such as the Puretic power block....

, and patented in 1953. In English, Puratić is usually spelt Puretic, sometimes Puretich.

While he was working as a tuna and sardine fisherman from San Pedro

San Pedro, Los Angeles, California

San Pedro is a port district of the city of Los Angeles, California, United States. It was annexed in 1909 and is a major seaport of the area...

, California, Puratić started thinking about the difficulty of hauling seine nets. The original power block he designed was essentially a simple winch which used a V-shaped roller coated with hard rubber. It was suspended from a davit

Davit

A davit is a structure, usually made of steel, which is used to lower things over an edge of a long drop off such as lowering a maintenance trapeze down a building or launching a lifeboat over the side of a ship....

, and powered from the warp end of the winch by a looping rope. In 1954, the power block was trialled by American purse seiners in the Pacific. They have evolved since then, and nowadays power blocks are powered by hydraulic pump

Hydraulic pump

Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic.Hydrostatic pumps are positive displacement pumps while hydrodynamic pumps can be fixed displacement pumps, in which the displacement cannot be adjusted, or variable displacement pumps, which have a more...

s. Their speed, torque and direction can be remotely controlled from the bridge during operations. As a result, retrieving the net is safer and requires less manual work.

Other important innovations of the same period were the development of synthetic fishing nets and sonar

Sonar

Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...

 detection devices. The combination of the automated power block hauling synthetic nets with sonar sensing revolutionised the industry.

The use of power blocks was found to have further advantages. It is possible to fish in rougher weather with the power block, because the steady force exerted by the net stabilizes the vessel. When deployments are made which miss the schooling fish, the net can be rapidly retrieved and redeployed on the same school. The power block also makes it easy to get nets aboard in emergencies, such as a sudden shift in tides or winds, or shark attacks on the catch and net.

On the other hand, the increase in the effectiveness of purse seine fishing led to herring schools choosing to school deeper in the water. Nets that could operate in deeper water needed to be bigger and heavier. That in turn meant bigger vessels, which pushed the smaller herring vessels out of business.

Details

Seine fishing industries rapidly recognized the value of the power block, and by 1960, most northern seine vessels were using the power block. Nowadays power blocks come with dozens of configurations and sizes. They are installed on over twenty thousand fishing vessel

Fishing vessel

A fishing vessel is a boat or ship used to catch fish in the sea, or on a lake or river. Many different kinds of vessels are used in commercial, artisanal and recreational fishing....

s across the major purse seining fisheries

Fishery

Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...

 around the world. These fisheries haul huge schools

Shoaling and schooling

In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...

 of tuna

Tuna

Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...

, salmon

Salmon

Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...

, herring

Herring

Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...

, sardines, anchovies and menhaden

Menhaden

Menhaden, also known as mossbunker, bunker and pogy, are forage fish of the genera Brevoortia and Ethmidium, two genera of marine fish in the family Clupeidae.-Description:...

from the sea, accounting for a large part the world total fish catch.

Between 1969 and 1979, the Puretic power block was pictured on the reverse side of Canadian five dollar banknote issues. In 1975 Mario Puratić was given the National Inventor of the Year Award by the Intellectual Property Owners Education Foundation for his invention of the power block.