The main boom of a model is linked to the mast by a swivel connector which allows the boom to swing from side to side.
Typically the boom on a model needs to kept from lifting when the sails are not trimmed in hard.
To keep the main boom from flying up a "boom vang" kicker a simple device is set between the boom and the foot of the mast. Vangs take a variety of forms from a trunbuckle, to a piece of fishing line to a line controlled by a servo to allow the boom to be pulled down or allowed to raise up.
