I was thinking up to £500 as a budget
Sailing photography is a very demanding type of photography, demanding not only on the photographer but on their gear. There was an interesting article a year or so ago with one of the top sailing photographers and the amount of gear that they carried with them was bloody scary, not just the amount of it but the cost! I'm talking serious money.
It goes without saying that these people don't use compact cameras and sadly £500 ain't going to be anywhere near enough to even dabble in the SLR range of cameras as the housing for a 400D comes in at over £600 on it's own (looking at about £1500 for housing, camera and lens)
Is not using a DSLR a big issue? Well yes and no. The quality of compacts these days are incredibly good and it's a shame that a lot of people incorrectly poo poo compact cameras thinking that an DSLR will suddenly make them a pro and/or allow them to take better photos. That said for the kind of photos you will want to take you would really, really benefit from an interchangable lens camera because there will be times when you will need a wide angle, fish-eye, telephoto and standard lenses not to mention the superior metering and performance of an SLR. However with SLR's you basically have two options 1) chuck the camera in an underwater housing but these will only fit a certain lens and you usually can't zoom and the housings on their own are more than your budget. 2) buy a weather sealed SLR body and lens something like the Canon 1DsMKII and Canon L lenses but just the lens one lens on it's own is more than your budget and these are only splash proof, if you boat rolls over or sinks.....goodbye camera!
So you basically have two options, buy a waterproof camera which, having had a brief look at a few models, arent exactly feature packed and although capable of taking acceptable images won't really worry the likes of Rick Tomlinson or buy a better compact and get an underwater housing for it. Now this is where it get's difficult. As I said before you may well find that you need a wide focal range from wide angle like 17mm through to telephoto at 300mm. Now there are compact cameras that do offer such a focal range however these cameras also have lenses that extend quite a long way. Because of this you typically can't find underwater housings for them because unless the lens of the camera always presses up against the glass 'port-hole' of the housing you'll get reflections and the photos will look crap. What this means is that you are probably going to be restricted to cameras with a much more limited focal range, probably something around 30mm to 120mm which is neither very wide or very long.
I'm not recommending any of these as I don't know too much about them other than what their spec is but take a look at:
Canon Digital IXUS 950 IS with Canon WP-DC15 Waterproof Case
Total: £370
Canon Digital IXUS 960 IS with Canon WP-DC19 Waterproof Case
Total: £430
If nothing else this will show what you can get for your budget.
HTH
