Ship loads

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Part of a series on vessels'

Structure

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Concepts

Ship Loads

Ship loads come in a variety of forms, from the environment, operation, and loading of the vessel.

Contents

Load Sources

Static Loads

Induced or present in the vessel while it is at rest.

  • Cargo carriage
  • Bouyancy
  • Drydocking
  • Operations aground

Dynamic Loads

A vessel in motion will experience a number of dynamic loads as the result of machinery vibrations and seaway interactions.

Low-Frequency Loads

Waves
Boat with wave-induced loading

Waves induce dynamic loadings both by induced variances in bouyancy along the length of the hull and water impacts from the resultant heaving, rolling, and pitching. Waves may vary in frequency, duration, height, and direction. An approximation of wave-induced longitudinal loading can be estimated by considering the ships hull centered on the crest or trough of a ship-length wave, and calculating the equivalent static stresses (i.e., as per Murray's method). While this number is quite the abstraction from a truely representative wave-interaction analysis (tedious, at best), the calculated number can be compared to calculated numbers for existing vessels which have proven sufficient in their service histories.

Inertial Accelerations of Equipment & Cargoes

High-Frequency Loads

High frequency loads, or common vibration, can be amplified and transmitted by structure; structures exposed to vibrations near their natural frequency can 'pick up' the vibration (resonance). This may be felt on many vessels, for example, as a shudder in a vessel as it accelerates & the engines rpm passes through the natural frequencies of structural elements. High frequency dynamic loads increase displacement & deflection of structural members, potentially leading to or accelerating fatigue failures.

  • Propeller Interactions (too close to hull, insufficient propeller immersion, unbalanced or damaged blades, pressure gradient across propeller disc)
  • Machinery Vibration
  • Flow around appendages
  • High-frequency waves (if resonant with some portion of the structure or hull, springing or whipping may occur)

Weather Loads

  • Thermal loads (hot above wl, cold below)
  • Ice loads
  • Wind loads

Impact Loads

  • Weapons discharge
  • Collisions & Allisions
  • Ordinance/explosions
  • Flight operations
  • Bulk cargo operations

Service Loads

  • Crane/Cargo Handling loads
  • Winching loads (towing, anchor handling, etc.)
  • Mooring Lines & fittings (winds,currents)
  • Firefighting Monitors
  • Loads induced from Launching (short term, but often quite high)
  • Icebreaking (typically, supersede all other loads in magnitude)
  • Pushing (i.e., tugs)
  • Low-temperature/high pressure cargo (i.e., LNG)

Types of Loads

Global Loads

Global loads act on the entire "ships girder", the vessel as a whole.

Local Loads

Loads experienced by stiffened panels, girders, beams, & stringers.

Design Loads

The most severe load expected on a given member, to which the member will be sized/designed.

See Also

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