If preordering shore excursions, tell your agent of your special needs. Also talk to the NCL shore excursions personnel onboard your ship prior to booking an excursion onboard.
Also from NCL's web site:
Wheelchair Users
Though NCL does have wheelchairs on board for emergency or isolated incidents, guests that require fulltime use of a wheel chair must provide their own. Motorized wheelchairs are welcome as well, however, they must be collapsible, three-wheel "Amigo-type." The chairs must be powered by gel-cell batteries. Due to safety regulations, NCL will not accept any wet-cell or acid battery-powered wheelchairs on board the ships. The wheelchair battery recharger must be adaptable to 110 voltage.
For the safety of all, wheelchairs may not be used to transfer from the ship to a tender.
NCL maintains a limited number of wheelchairs on our private island, Great Stirrup Cay, that are specially designed for use on sand. They are available on a first-come, first-served basis.
Physically Challenged Guests
While NCL strives to make its Shore Excursion program available to all its guests, inherent tour venue limitations and/or tour operator limitations exist that are beyond NCL’s control that limit the ability of guests with special needs to participate in certain Shore Excursions.We urge such guests to advise the Shore Excursion department of special needs when pre-booking tours and to further meet with the Shore Excursion Manager on board to discuss their special needs as they relate with the unique characteristics of each Shore Excursion.We typically recommend independent transportation for the comfort and convenience of guests with special needs.