Chapter 3 provides an introduction to the sea loads that act on ship structures, focusing on environment-related and transient loads. A hypothetical but realistic scenario of a loaded voyage of a bulk carrier is presented, and is used to identify and subsequently classify all loads that act on the hull girder. These are classified as environment-related, hull girder-related, mechanical equipment-related and cargo-related. The sources of environment-related loads are then discussed. These include hydrostatic pressure, wave loads, thermal gradients, ice loads, wind pressure and related variations on a geographic and temporal basis. Transient wave loads are then discussed (bottom slamming, bow flare impact and deck wetting), followed by a discussion on springing. The discussion of slamming includes hydroelastic effects. The need for nonlinear analysis in estimating springing and whipping loads is discussed in the last section of the chapter.

Hydroelastic problems involve dynamically coupled, structurally elastic, hydrodynamic systems. The fluid can have many effects such as added inertia, additive hydrostatic stiffness, increased system damping, or external excitation (e.g. wave impact, variable current forces, etc.). This chapter illustrates some of the aspects of hydroelastic problems by deriving fundamental relationships and discussing a specific example - ship springing. Springing vibration is differentiated from whipping vibration by the source of excitation. Springing is excited by synchronous matching of the natural frequency with the incident wave encounter frequency while whipping is transient vibrations due to impact/slam loads. A well-developed energy method - the Rayleigh-Ritz method - is applied in the determination of fluid-structure resonance. For general marine vibrations, energy methods may be used when free surface effects are small or negligible. Fluid inertia effects are calculated using strip theory and Lewis form coefficients. Limitations of strip theory are discussed. A spherical globe mounted on a flexible pole submersed in water is given as an example of a hydroelastic system.