Grade is related to Regular. Regular is related to Quality. Quality is related to Skilled. 
Gang is a synonym of Crew. Crew is related to Boat. Boat is related to Port. 
Grade <--RelatedTo--> Regular <--RelatedTo--> Quality <--RelatedTo--> Skilled 
Gang <--Synonym--> Crew <--RelatedTo--> Boat <--RelatedTo--> Port 