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In an A-frame derrick, the tower is set up from two poles or masts with their bottom ends spread from each other and their top ends joint together. There are crossbars to connect the two poles, forming a letter "A" shape tower. The tower is ground anchored to provide support. A boom is hinged from the lowest cross bar and extends outward and upward. The top end of the boom is connected to a pulley system which is connected to the top of the tower. Manipulating the pulley system will allow the boom to change the angle against the tower. There is another pulley system to connect to the top of the boom for load lifting. When an A-frame derrick is used in a vessel, it is called floating A-frame derrick.

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