Gosh, all these posts - thanks so much guys!
Have been getting on with it and pondering.
There are some really good suggestions here and some brilliant explanations of why some work and others don't.
I think SparklePop is spot on about why The Shipwreck isn't good, and others might work better. At this stage I'm trying to catch the attention of an agent so something teens will think cool does make me look more clued up - The Shipwreck would make it look as if I wasn't really aware of what was going on in publishing for the age group. I wrote it 100% for me and didn't try to be cool - I have tried to make it good and well-written rather than to make it cool - but packaging it as cool seems well worth doing. (Not that it's not cool )
I like 'wrecked' more than 'beached', though beached is deffo good, because bearing in mind what people have said about using words from within the text, the characters do talk about being 'wrecked' but don't talk about being 'beached.' Also, although it is not a major theme, alcohol may have just been slightly involved in the wreck happening. Plus there are wrecked relationships as a result of it.
The only thing that does make me wince a bit with 'wrecked' is it sounds a bit like I'm trying to be all Melvin Burgessy and writing about drugs etc when frankly it is more Swallows and Amazons than Junk. (though cool Swallows and Amazons, obviously).
What I like about Oceanspace is that it kind of adds something to the atmosphere, the sense of the hugeness of the Pacific. Space, distance, is a theme even before the wreck happens and after they are off the island.
The north American associations of 'ocean' are good because one of the families is American. It's from a Robert Service poem called The Three Voices - 'The waves tell of ocean spaces,
Of hearts that are wild and brave,
Of populous city places,
Of desolate shores they lave,
Of men who sally in quest of gold,
To sink in an ocean grave'
One of the characters quotes the odd poem from time to time and this sounds like her taste, too!
But I am worried about the 'sounds like fantasy' aspect of it.
PMSL @ Witchandchips' suggestions