Depends on how your judge, and your club, looks at it... it COULD fly as a landscape, but you're just as likely to get thrown 'out of category' because it IS a seascape - there *should* be a certain percentage of land in the image...
The orientation is indeed 'landscape', as opposed to 'portrait', but I think you'd need to plan to lose if you're going to argue the orientation of a shot makes it eligible for a competition - that's like trying to enter a 'portrait' oriented shot of a tree on a hilltop into a portrait competition and wondering why you're ruled out... Can you take a picture of a tiger in landscape orientation and legitimately call it a landscape, if all you can see is a little grass under it's front paws??
Cheers,
Stuart
P.S. I love the shot - and it's something different, so you'll either get great points, or crap points... either or - I doubt any judge would be undecided about it...