IACS updates Rec 34 with new wave scatter diagram

IACS Recommendation No. 34 describes wave statistics intended for design of sea-going ships above 90 meters including the effect of bad weather avoidance. It is based on North Atlantic trade, which represents the most severe conditions ships tend to operate in. 

The new scatter diagram and wave spectra defining design environmental conditions will be used for wave load, fatigue, and seakeeping calculations. Accurate Wave data remains of paramount importance as this data is used to represent the ocean environment, underpinning wave load prescription, which in turn, greatly impacts hull structural requirements.

The second revision of Recommendation No. 34 (Rev.2) was published following the conclusion of a long-term review of wave data, which was begun in 2016.

The review had been tasked with investigating whether, and how, Recommendation No. 34 could be improved using more recent data sources, with modern data showing both an increase in mean significant wave height for the North Atlantic and that more extreme weather is being experienced in recent years, including the existence of rogue waves and the possible effects of climate change.

Improved data sources

Several sources of wave data, including altimetry (measurements from satellite), hindcast model (re-analysis of past weather), and wave buoys were used to derive the scatter diagram from a combination of vessel tracks and hindcast wave data. These new, more modern, data sources represent a significant improvement in the quality of data, given that previous wave data was collected in the second half of the 20th century from visual observations on board ships.

The IACS Project team Global hindcast datasets are built on global coverage over an extended period of time and have been analysed and validated through the use of measurements from buoys and altimeters. By taking into consideration publicly available AIS ship position data, this allowed the wave data to be mapped to actual ship position & time when generating the corresponding statistics whose analysis showed that bad weather avoidance had a significant impact on the wave statistics of the sea states encountered.

The resulting updated simple scatter diagram, using validated datasets of wave data and ship positions will facilitate more accurate estimation of design loads such as pressures, motions, accelerations, hull girder loads, all contributing to the improved standardisation of safety levels of the fleet. This data will be used by individual Classification Societies when reviewing their current rule requirements including, by IACS Members, for Common Structural Rules. This significant new data source will also be of value to other industry stakeholders who use wave data for individual projects.