Offshore Crane Luffing Sheave Swiveling for Long Boom Cable Alignment
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Solution Overview
Problem
Existing cranes face issues such as alignment, friction, abrasion, and kinking due to increased boom length and dimensions, particularly in handling components of offshore wind turbines, which require tall cranes for heights exceeding 100 meters and significant masses up to 150 tons.
Innovation Solution
The offshore leg encircling crane features a movable mounting of luffing cable sheaves with swivelling motions about vertical and horizontal axes, allowing proper guidance of luffing cables over a range of positions, preventing issues like alignment and friction, and accommodating elongated booms with relatively small head structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the boom length is increased to handle components at greater heights, then the crane can reach higher positions (over 100 meters), but alignment problems, friction, and kinking occur in the luffing cable system
Solution Approach 1:
The luffing cable sheaves are made movable rather than fixed, allowing them to swivel about vertical axes. This dynamic adjustment capability enables the cable routing to adapt to varying boom positions and angles, preventing alignment issues and kinking that would occur with a rigid fixed mounting system when operating with extended boom lengths.
Solution Approach 2:
The invention changes the positional parameters of the luffing cable sheaves by allowing them to swivel about vertical axes. This parameter change enables the cable path to be dynamically adjusted according to the boom's position, maintaining proper cable alignment and preventing friction and kinking issues even when the boom is extended to great lengths.
2Area of moving object
If the head structure width is kept relatively small while boom length increases, then the crane maintains operational efficiency, but the luffing cable alignment becomes problematic
Solution Approach 1:
By making the luffing cable sheaves movable with swiveling capability about vertical axes, the system dynamically adjusts cable alignment rather than relying on precise fixed geometric relationships. This allows the head structure to remain compact while the cable routing automatically adapts to maintain proper alignment regardless of the extended boom length.
3Strength
If jack-up legs of increased dimensions are used to support taller cranes, then the vessel can support greater loads, but the width of the boom at the boom connector increases
Solution Approach 1:
The movable luffing cable sheaves with swiveling capability compensate for the increased boom width resulting from larger jack-up legs. The dynamic adjustment allows proper cable routing and alignment even when the boom connector width increases, maintaining luffing system reliability despite the necessary structural enhancements for supporting taller cranes.
Data Source
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AI summary
Crane (10), in particular an offshore leg encircling crane for use on a jack up-vessel (1). The crane comprises a revolving superstructure (11) with a crane housing (13) to which a boom (20) is connected. The crane further comprises a hoisting system and a luffing device for pivoting a boom up to an upright position and down. The luffing device comprises first left-hand and right-hand luffing cable sheave sets (45; 46) provided at opposite sides at a top of a luffing frame structure (18c), and second left-hand and right-hand luffing cable sheave sets provided at opposite sides of a head structure of the boom. A variable length luffing system (41) extends from the luffing winch (40) via the first left-hand and right-hand luffing cable sheave sets to extend in a luffing direction to the second left-hand and right-hand luffing cable sheave sets.