This document outlines detailed guidance for planning, designing, and building slipways at ports and harbours. It addresses site evaluation, cradle and slipway structural design, load handling, foundation prerequisites, and operational factors essential for effective vessel haul-out facilities. The standard supports marine and civil engineers in delivering robust and reliable slipway infrastructure.
Overview
This document outlines detailed guidance for planning, designing, and building slipways at ports and harbours. It addresses site evaluation, cradle and slipway structural design, load handling, foundation prerequisites, and operational factors essential for effective vessel haul-out facilities. The standard supports marine and civil engineers in delivering robust and reliable slipway infrastructure.
Audience
Contents
Structure
This section defines the scope of recommendations for the planning, design, and construction of slipways as per Clause 3.1. Terminology follows IS 7314-1974. Numerical rounding should adhere to IS 2-1960, preserving significant digits. The standard harmonizes international best practices with Indian field conditions, providing a framework rather than explicit design formulas.
Comprehensive site investigations are required, incorporating topographic, oceanographic, and geotechnical data in accordance with IS 4651 (Part 1)-1974. Data includes elevation, seabed profiling, tidal and wave data, soil stratification, groundwater levels, and soil strength tests such as SPT and CPT. This ensures accurate foundation design and structural safety.
Design of cradles must consider the maximum load derived from either sue load or distributed load calculations. Slipways are designed for this maximum load along the upper two-thirds, with only the cradle's self-weight considered on the lower one-third. Dynamic effects, environmental loads, and safety factors per IS codes must also be incorporated.
Slipway length is calculated using vessel dimensions, slipway slope, draft, and block height. Recommended slopes range from 1:12 to 1:30, with 1:15 preferred for smooth operations. Cradles typically include multiple rollers arranged to evenly distribute vessel weight, supported by headblocks, winches, and downhaul extensions.
For soils with adequate bearing capacity, spread or mattress foundations beneath tracks connected by concrete slabs are advised, alongside sheet pile cut-off walls to prevent scour. In weaker soils, piled foundations with reinforced concrete pile caps and steel rail supports are recommended to ensure stability and minimize settlement.
Cradle types include rigid (fixed), semi-rigid (partially flexible), and telescopic/collapsible (adjustable length). Supports must accommodate load transfer, thermal expansion, and vibration effects. Live roller or wheel and bearing systems facilitate movement. Load calculations incorporate pipe weight, thermal forces, and dynamic impacts, with support spacing based on pipe diameter.
The pulling force on hauling chains is calculated factoring vessel and cradle weight, slipway slope (tan θ), and friction coefficients (0.035 for wheels, 0.04 for rollers). Accurate weight assessment and friction values guide the selection of hauling equipment capacity and chain strength to ensure safe vessel movement.
Load distribution on cradles is determined by segmenting the vessel below the light draft waterline, calculating segment volumes, and multiplying by seawater specific gravity (~1.025). Sue load, a concentrated load at cradle contact points, is computed by analyzing moments and volumetric displacements. Design uses the higher value between sue load and distributed load.
Construction includes specifying 1.5 m wide wall footings with 10 cm concrete slabs over slopes. Foundations utilize spread or mattress types linked by concrete floors, with sheet pile walls at the water-end for scour protection. These methods ensure structural integrity and durability in marine environments.
Operational guidelines focus on prestressing concrete systems, referencing IS 7314-1974 for definitions. Tensioning forces are calculated as product of prestressing steel area and ultimate strength, accounting for losses due to elastic shortening, creep, shrinkage, relaxation, and friction. Equipment calibration and force monitoring ensure effective prestress application.
Safety and maintenance emphasize providing 60 cm clearance above vessel draft for safe slipping, maintaining 10 cm concrete slab thickness on footings, and conducting regular inspections of slipway surfaces and turntable mechanisms. Rounding of numerical results must comply with IS 2-1960 for consistency.
Frequently Asked
Key considerations include conducting detailed topographic and hydrographic surveys, ensuring site conditions meet general suitability criteria such as accessibility and wave protection, and evaluating soil and foundation characteristics. Preferably, the site should have incompressible or uniformly settling soil; if soft mud or siltation risks exist, pile foundations are recommended. Construction feasibility, including accurate pile driving and stable footing provision, is also essential.
The vessel length is segmented below the light draft waterline, with volumes for each segment calculated and multiplied by seawater’s specific gravity (~1.025) to determine segment loads. Load diagrams are plotted and enveloped to form a cradle load distribution curve. Sue load, representing concentrated loads at cradle contact points, is assessed through moment and volume analyses. The design employs the greater of the distributed load or sue load for safety.
Recommended cradle types include rigid cradles, offering high stability with fixed geometry; semi-rigid cradles, providing limited flexibility to absorb minor hull stresses; and telescopic or collapsible cradles, which allow adjustable length for handling varying vessel sizes and ease of storage. Cradles also incorporate keel and bilge blocks for hull support, with design tailored to live roller or wheel-bearing support systems.
For soils with good bearing capacity, spread or mattress foundations beneath rail tracks, connected via concrete floor slabs and protected by sheet pile cut-off walls, are suitable. In conditions with low bearing capacity soil, piled foundations with reinforced concrete pile caps and mild steel rail supports spanning pile bents are preferred. Foundations must prevent uneven or excessive settlement to maintain structural and operational integrity.
Haulage systems should use winches to move traversing cradles mounted on cross rails, interlocked with fixed rails on side berths for stability during lateral movement. Turntable arrangements may be used for small vessels in multi-berth layouts. Mooring facilities must secure vessels firmly during positioning, using fixed dolphins or lead-in jetties equipped with bollards and fairleads to prevent drift, and align slipways to minimize exposure to strong winds or currents.
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