Many smaller fishing vessels rig paravanes to improve stability. This is especially true of some of the herring seiners, because they carry considerable top hamper. The seine gear itself, with a heavy boom with winch on the end adds to weight high up, but so too does all the pumping apparatus, consisting of chutes and conveyors.
The paravanes, similar to those rigged by ships during World War II to fool acoustic torpedoes, consist of fish shaped objects, suspended from long booms. When the booms are extended, the actual paravanes (fish) are dropped into the water and towed along. The drag they create compensates for the top hamper of the boat. They only work once boat is moving at some speed.
These photos show Dual Venture sailing this afternoon and getting ready to set her paravanes as she goes.
1. Getting away from the dock. Booms in upright (stowed) position.