Splash Zone Crossing
Lifting through the splash zone is a key application area for Cranemaster. Many hundred spool systems, mud mats, manifolds and suction anchors have crossed the splash zone successfully supported by a Cranemaster® unit.
Limited operational weather window due to dynamic loads.
Large forces on structures during crossing, especially complex structures and structures with large horizontal surfaces (e.g. manifolds).
Crossing of structures with large variation between weight in water and air.
Reduction of dynamic force in payload and lifting points during splash zone crossing.
Reduction of dynamic load on the crane tip and the hoisting system.
Reduction of probability of slack wire during splash zone crossing.
For challenging applications, Cranemaster® Advanced Splash Zone Tension Mode (CAST) will give unsurpassed performance in terms of low DAF and the ability to avoid slack slings even for large objects and high waves.
Objects for which particular benefits are offered
- Objects with a large horizontal surface independent of their weight, e.g. mud mats, protection covers and manifolds.
- Objects which have a large difference between weight in water and weight in air, e.g. suction anchors and closed pipes.
Cranemaster® will protect the crane, catch snap loads and also catch slack in the hoisting wire as the load is lowered through the splash zone.
Splash zone crossing with and without Cranemaster®
This Orcaflex simulation shows a splash zone crossing of a manifold structure. As seen, significant reductions of forces in load and crane may be obtained by using Cranemaster® (to the left). The stability increases and the DAF is reduced from around 5.0 to 1.1. The minimum tension in the crane wire is not acceptable without Cranemaster® (to the right).
Structure dimensions: 10 x 10 x 7 m • Structure weight in air: 50 t • Structure is lowered at a speed of 0,3 m/s • Significant wave height (Hs): 2.5 m • Wave period (Tz): 6 sec.
Cranemaster® in action through the splash zone
- Slamming forces, added mass and drag of the object can increase the forces transferred to the crane and the object by many times the weight of the object.
- Snap loads caused by wave or boom-tip motion may be very large.
The general principles and issues are thoroughly described in Recommended Practice DNV-RP-H103 from April 2011.
With Cranemaster® mounted, these forces will be removed or reduced significantly. The main functionality of Cranemaster® is to decouple the movement of the boom tip from the movement of the load. The spring force of Cranemaster® will support in avoiding slack wire during the splash zone transfer, while excessive forces in crane or load due to wave and boom tip movements will be removed by a combination of the spring and dampening forces of the Cranemaster® unit.
Selection and tuning
- The maximum stroke of Cranemaster® should be longer than the boom tip movement.
- Cranemaster® should have a spring response corresponding to the maximum allowable forces on load and crane.
- Cranemaster® should have dampening forces tuned according to the expected boom-tip and characteristic vertical water particles accelerations.
- A slack wire may be acceptable since the snap load will be picked up by the Cranemaster® unit. However, stability of the load may be a concern and it should therefore generally be avoided.
- A full stroke is not acceptable since the Cranemaster® unit then will give no protection. A safety margin of 5%-15% of maximum stroke is recommended.