Fire officials are investigating the caus of a small explosion on a 43-foot fiber glass yacht this morning that left a 58-year-old man hospitalized in serious condition with burns.

Initial reports indicate that the sport yacht — Seven-Eleven — was being fueled at 9 a.m. at a boat slip behind the Hawaii Prince Hotel when the explosion occurred, Capt. Terry Seelig, Honolulu Fire Department spokesman said.

Damage was extensive to the deck and cabin of the yacht, estimated in $100,000.

There were two people on board, but only one was injured.