I'm not sure that this is correct in the Yacht Club! The service level is extremely high, I think. If you tell your butler, or any butler you see, that you will spend lots of time on your balcony and should appreciate (I don't mean tip a lot but of course they deserve a good tip!) if they come by sometimes and ask if you want anything, I'm sure that they will do that!
Of course you can also use your phone and call them when you want something.