Both sorts available: North American standard, 110 volts AC. or European standard (220 volts AC, round prongs). Stateroom outlets can accommodate appliances up to 1500 watts.
I was on the voygerof the seas and i took an american adaptor with me for to use my ghd which i used every night .
If the red light doesn't flash so quickly you may need to wait longer for them to heat up. Also, most models have the euro fitting inside the UK plug. Otherwise, use an adaptor. As previously said, you will have a choice of outlets, though bigger percentage in North American 110v.
Certainly couldn't cruise without the GHD's!