Abstract: A backup heave compensation system and an associated lifting arrangement are for a floating drilling vessel comprising a rig structure with a primary heave compensation system. The backup heave compensation system comprises: a vertically extendable and retractable lifting arrangement; a hydraulic system operatively connected to said lifting arrangement; and a control system operatively connected to said lifting arrangement and hydraulic system for selective control and operation thereof. The lifting arrangement comprises: a rigid frame structure comprised of: at least two vertically extending cylinders; a first transverse element connecting first end portions of said cylinders; and a second transverse element connecting second end portions of said cylinders; and a portal structure comprised of: at least two vertically extending piston rods having first end portions provided each with a piston; and a transverse portal element connecting second end portions of said piston rods.