For it is during ship arrivals and departures, when most ship collisions or groundings occur. Hydrodynamic constraints include the ability to withstand shock waves, weather collisions and groundings. The Great Lakes have a long history of shipwreck, groundings, storms and collisions. Accidental boat groundings can obliterate areas of coral reef. Scarring of seagrass beds by vessel groundings or propellers is a significant problem. A Boeing pilot used "egregious" in describing an issue with the Boeing 737 MAX groundings. Boeing said that the total cost of groundings approached $8billion as of July 2019. Similar damages could be observed in sister ships which where involved in groundings, too. Michael Devitt claims that repeated groundings in an object can account for reference change. Cannabis is usually smoked during groundings,although some practitioners also smoke it informally in other contexts. One of the central activities at groundings is "reasoning". It can lead to unexpected groundings and handling difficulties. Research focuses on the identities of the speaker and the addressee, and their historical groundings. The groundings would eventually last until September 14. The company reported a $2.9billion loss due to the groundings.