A hydraulic mooring system comprising at least two hydraulic mooring cable holding devices (14a,b), located on a quayside to exert pulling forces with opposite direction components along the direction of the quayside on mooring cables connected to a same ship, wherein each of the hydraulic mooring cable holding devices (14a,b), comprises - a hydraulic cylinder, a piston in said hydraulic cylinder, and connections to said hydraulic cylinder and said piston for connecting the device (14a,b) in a mooring cable connection between the ship and a mooring point, - an overpressure protection part coupled to a first end of the hydraulic cylinder at which hydraulic pressure will build up when the mooring cable connected to the hydraulic mooring cable holding device (14a,b) comes under tension, the overpressure protection part comprising a main reservoir containing gas and hydraulic liquid, the overpressure protection part comprising an overpressure valve and a one way valve, coupled in parallel to each other between the hydraulic cylinder and the main reservoir, the overpressure valve configured to pass hydraulic liquid from the hydraulic cylinder to the main reservoir when a difference between a first pressure in the cylinder and a second pressure in the main reservoir exceeds a first threshold value, the one way valve configured to pass hydraulic liquid from the main reservoir to the hydraulic cylinder when the difference drops below a second threshold value, lower than the first threshold value; - an auxiliary reservoir coupled to said first end of the hydraulic cylinder, the auxiliary reservoir containing gas and hydraulic liquid, the main reservoir having a first pressure-volume change characteristic that differs from a second pressure-volume change characteristic of the auxiliary reservoir, in the sense that the pressure in main reservoir changes less than the pressure in auxiliary reservoir for equal exchanges of volume of the hydraulic liquid from the hydraulic cylinder. - a hydraulic cylinder, a piston in said hydraulic cylinder, and connections to said hydraulic cylinder and said piston for connecting the device (14a,b) in a mooring cable connection between the ship and a mooring point, - an overpressure protection part coupled to a first end of the hydraulic cylinder at which hydraulic pressure will build up when the mooring cable connected to the hydraulic mooring cable holding device (14a,b) comes under tension, the overpressure protection part comprising a main reservoir containing gas and hydraulic liquid, the overpressure protection part comprising an overpressure valve and a one way valve, coupled in parallel to each other between the hydraulic cylinder and the main reservoir, the overpressure valve configured to pass hydraulic liquid from the hydraulic cylinder to the main reservoir when a difference between a first pressure in the cylinder and a second pressure in the main reservoir exceeds a first threshold value, the one way valve configured to pass hydraulic liquid from the main reservoir to the hydraulic cylinder when the difference drops below a second threshold value, lower than the first threshold value; - an auxiliary reservoir coupled to said first end of the hydraulic cylinder, the auxiliary reservoir containing gas and hydraulic liquid, the main reservoir having a first pressure-volume change characteristic that differs from a second pressure-volume change characteristic of the auxiliary reservoir, in the sense that the pressure in main reservoir changes less than the pressure in auxiliary reservoir for equal exchanges of volume of the hydraulic liquid from the hydraulic cylinder.