Swim trunk and board shorts may appear similar but they solve different purposes. Swim trunk are shorter in length than boardshorts. Swim trunk comprises of mesh lining inside the cloth and they have elastic waist whereas boardshorts does not have any lining and they have waist drawstring to be fitted.
For Surfing: While catching the waves on sea no one wants their swimwear to become obstacle.Swim trunk have the mesh lining for the support but it hinder the leg movement during high speed turn and to solve the purpose board shorts have come up. Board shorts are made up of polyester and nylon without the inner lining.
Wake-boarding: Wakeboarding is a hybrid sports. Preference is given to both swim trunk and board shorts for wake-boarding as both protect the skin. Because board shorts fit below the knees hence they are highly preferred by wake-boarders. During high impact tricks board shorts remain in place because of their design and this is the reason that they are prefered over swim trunks.
Chill Out: Board shorts serve the same purpose as swim trunks when someone is lounging on the beach with friends and family. Because swim trunks are short hence they expose greater area to sun rays which results in tanning while board shorts shield the major part of leg and hence protect the leg from getting tanned. Big mens board shorts are highly preferred for beach lounging over swim trunk.