Have you had a good perusal of my weddings in Tenerife page? For a blessing ceremony on a boat, I imagine that any of the three wedding planner services whose links can be found there can organise that.
Although it never seems to get mentioned, I imagine they'll be able to sort out a minister too.
For sorting out a minister yourself (if you want an Anglican one), then it's worth checking out the St Francis Anglican Chaplaincy website here. They appear to have a new section on their site, dealing with wedding blessings.
