The only cruise line that offers 7-night cruises that begin and end in Hawaii is NCL America, with US-flagged ships, the Pride of Aloha and Pride of America. The Pride of America was even partially built at a US shipyard. Because these ships are US-flagged, with US crews, they don't have to go to any foreign ports to comply with US law.
NCL America's early cruises on the Pride of America received all sorts of bad press. It seems that NCL underestimated how hard it would be to hire, train, and retain American crew members. NCL America was unable to provide decent service and decent meals on early cruises. As you might guess, NCL went into high gear to correct the deficiencies, but tha bad publicity still lingers.
From CruiseCritic, here are reviews of the
Pride of Aloha and the
Pride of America.
NCL also offers 10- and 11-night cruises that begin and end in Hawaii on the foreign-flagged Norwegian Wind, with four full days at sea to get to and from Fanning Island in the Republic of Kiribati.
Other cruise lines have a limited number of Hawaii sailings, typically involving Vancouver, Canada, or Ensenada, Mexico. Some are 14-night cruises, such as Celebrity's 14-night Hawaii cruises that begin and end in San Diego. Others involve 1-way voyages to or from the West Coast.
I've never taken a Hawaii cruise, but, as this post indicates, I've researched the options. In the end, I don't think we'll do a Hawaii cruise. I'd rather go to Alaska or the Southern Caribbean. However, a cruise could be a good way to sample the islands of Hawaii, especially for those who have never been to Hawaii or who have only visited one island.