The Dark Tides by Mark Piggott

http://www.amazon.com/dp/B00QGETZ3W

The Drake family family has known more than its share of tragedy at sea. After the devastating and mysterious loss of their patriarch, Bryan, to a strange storm, his wife and children are caught in a storm freakishly similar to the one that took him from them. An accident becomes a joyous reunion, as they find him alive and well but equally stranded on the mysterious island of Avalon, where the descendents of King Arthur rule a world filled with knights, elves, dwarves ... and magic! Lord Bryan MoonDrake--as he is now known--has attained the rank of the Gil-Gamesh, protector of the realm. He helps his wife and children adjust to their new life on the magical island.

But all is not well in the kingdom. Dark forces arise to fulfill a prophecy to resurrect Morgana le Fay, the most powerful sorceress in the history of Avalon. If successful, she will unleash the Dark Tides to destroy the line of Pendragon once and for all. To save his family, his new home, and his king, can the Gil-Gamesh overcome incredible odds and powers beyond his comprehension to rid Avalon of Morgana's evil forever?