Question?

You obviously have good reason to be a vegetarian, would the fact it isn't the perfect diet for sailing change your views?

Okay I like to think of myself as a bit of a "sports nutrition expert" so I'll tell you what I think....

I presume if you're 5.5 stone you sail a laser 4.7?
For a start, protein supplements are a bit of a tricky subject and you need to know what you're doing with them.  A lot of the stuff is rubbish and with any protein supplement you need to be doing a lot of physical exercise and particularly weight training to build muscle not fat.  You also have you remember that you're 15 and will never get any slimmer/youthful looking and the butch, pumped up look isn't really that attractive to most boys.  But I can recommend maximuscle promax or cyclone as very good protein, glutemine and creatine supplements. 
You should have no worries about your vegetarian diet - in my opinion it's very healthy and I know lots of top athletes who are vegetarian.  At 15 you've probably got some a bit of growth still in you, how tall are you? 
When you say "performance sailing" I presume you mean high level competition sailing in which case a lot of your performance on the day will be down to your diet in the fe days leading up to the comp.  Carb loading is one school of thought where you can deplete your carbohydrate stores about 6 days before a major event  by eating hardly any starchy foods like pasta, bread, potatoes etc. and exercising way more and then gradually build up your carb consumption and taper off your exercise until a day before the event you are eating a lot of high carb food and resting your body completely.  This way your body makes sure it stores more carbohydrate than it had before so will give you that bit more energy to keep hiking on those long beats.  It's also important that when you get ashore you refuel with carbohydrates within 2 hours of getting back otherwise you will be totally shattered the next day and will feel sh*tty.  I tend to find a good big bowl of porridge in the morning will keep you going for aaaages and then maybe some fig rolls later into the day to keep energy levels high.  Porridge is magic stuff and It keeps me going through some gruelling cycling races and sailing is much the same. 
Oh yeah and energy drinks are a waste of time - water's the stuff!!
At 5.5 stone I think you might be a bit light for laser sailing where there's a lot of work involved - you might be better to go into a double hander like an rs200 and get yourself a big heavy crew....
I'm 5' 7 and 9.5 stone and i consider myself to light for competitive single handed sailing so you might want to rethink your boat choice there....

I think I might have gone a bit overkill on the initial question but it is a bit of a specialist area for me!

PB

there is nothing wrong with being a vegitarian, but they have conducted science expertiments and basicly it is easier to eat the right sort of food if you are not vegitarian. The only nutrition you will find harder to have enough and the right sort of is protien. Most top athletes that are exercising alot have to make sure that they eat enough protien, which normally envolves lots of chicken and tuna. Chicken and tuna are very very low in fat but have lots of protien, so they are perfect. At 15 stay well clear of any supplements, they only work if you do alot of exercise and at 15 bulking up is not good, also they are lots of them out they that are illegal to take in sailing and if you get drugs tested then you will get a ban. Everyone will say I have never been drugs tested sailing but if you sail a laser or radial and do a national ranker or qualifier then everyone there can be drugs tested and the EIS normal turn up to every single one.

as long as you are getting enough carbohydrate, protein, vitamins and not to much fat (esecially saturated) then you should be fine. At 35kgs you are on the light side for an oppy! You will just have to weight until you grow if you start doing wieghts or bulk up you will do damage for when you are older.

I've been veggie pretty much all my life and sailing pretty much all of it too...For protein I'd recommend diary, eggs, peanut butter and beans, but possibly not all in the same meal...Putting on weight has never been a problem for me (I wish) but that might have something to do with Cider, pizza and Chocolate...

The scientific studies are usually done by the energy drinks manufaturers themselves and so are usaully a bit unreliable.  The rehydration is no quicker than simple water and the replacement of salts shouldn't be needed if you are eating the right stuff.  The simple sugar form of carbs is one of the worst because it gives you a quick burst of energy and then very soon a big low where you'll feel drained.  The amount of sugars in the isotonic drinks is huge and if you're working along the principles of needing sugar for sport you might as well just drink a can of coke out there.  I always feel I perform a lot better by eating food like a cereal bar or fig rolls and drinking water than by drinking isotonic drinks.