The type of structure upon which the crane is mounted (i.e.In the case of floating installations, accelerations and inclinations additionally impact both the blue onboard and green offboard columns.įor a purchaser to ensure they purchase the correct crane for the job, providing the following is the best way to start: Examples of these parameters include boom length, significant wave height, wind forces and how high the crane is above the water. It is also important to note that numerous parameters will cause the green offboard ratings in the table to increase or decrease. However, if the purchaser wants to lift 100 tons from a supply boat, the minimum crane size from the green offboard columns will be in the range of the much larger Seatrax S9024, since that crane is the minimum sized model with at least a 100-ton rating. The Seatrax S4820 carries the 100-ton structural rating at minimum radius with a 60-foot boom. Using the “100-ton crane” example, let's take a look at the red columns. Note: All tons are short tons of 2,000 lbs. The boom foot pin elevation is assumed to be 110 feet above the water. Green column: the maximum weight that can be lifted in full compliance with API 2C, for the boom lengths and radii shown, for offboard supply boat lifts, with a significant wave height of 7 feet and a 30-knot wind, from a bottom-supported structure. Red column: the theoretical weight that can be suspended from the boom tip with the boom lengths and radii shown without exceeding the API 2C allowable stresses for onboard lifts from a bottom-supported structure.īlue column: the maximum weight that can be lifted with the hoists and wire ropes normally supplied for the boom lengths and radii shown in full compliance with API 2C for onboard lifts from a bottom-supported structure. The various columns are categorized by capacity or ratings basis, specifically: The table below lists the API Specification 2C ratings for typical Seatrax crane models. Therefore, the offboard supply boat capacity is reduced from the onboard deck lift capacity.

Offboard/supply boat lifts have the potential to impose impact loads on the crane that are not experienced during onboard/deck lifts. In addition, lifting a load off of a supply boat pitching in waves (offboard Lift) is treated differently than lifts from the deck of the installation the crane is mounted on (onboard Lift). In fact, because the offshore crane is fixed to the host structure, the distances from the crane at which various loads are to be lifted are more likely to determine the crane size rather than the maximum weight the crane will lift. However, the maximum lift weight to be lifted only partially defines the crane size. Seatrax often receives inquiries such as, “We need a 100-ton crane”.

Offshore Cranes for the Petroleum Industry

Crane lifting plan under 2000 lbs