Book title

[fatcat]

Ok, bit of a long shot but here goes. Book title and author gratefully received. I read this as a teenager about twenty years ago. It's about a teenage girl who spends her summer hols staying near the coast (with her grandparents I think). I think she discovers some kind of shipwreck or something to do with a boat and basically she experiences poltergeist activity. I think the ghost's name is Scoby and he's trying to tell her how he died or something like that. I remember she befriends another teenage girl and boy and also two priests, one of whom was called De Souza who helps to sort of exorcise Scoby and this other ghost. Does this ring any bells with anyone? Thanks.