Our hitchhiker

This bird landed on the boat one day and stayed for 4 days - he seemed tired. We fed him bits of bread and left a bowl of water. He eventually flew away as we passed some islands. We never did discover what he was as unfortunately the only bird book aboard is for landbirds of Fiji. If anyone knows I'd really appreciate knowing. He was a dark grey with a lovely white bit from his beak up over his head and white-rimmed eyes.