Classification Aspects of Ship Flexibility [and Discussion]

The main bending stresses in a ship's hull result from weight, buoyancy and hydrodynamic forces and are normally calculated satisfactorily assuming the ship does not vibrate. However, the ship will vibrate when it impacts with waves or if excited by waves of frequencies close to its natural frequencies. The calculation of these generally smaller vibratory stresses is much more demanding. The paper discusses all the mechanisms which can cause a ship to flex and the analysis techniques for evaluating the resulting lifetime stress effects. By comparing these with statistics from service experience or full-scale measurements, simple rules are devised and validated to ensure that ships can withstand a lifetime of bending, vibration, or both, without failure.