Sorry about such a long delay in answering, it has been busy.
Some fruits sink, but most float and form a cap while the fermentation is progressing. It is standard practice to punch the fruit down to better mix it with the liquid and aid extraction of flavors, but the skins and seeds are usually separated from the wine by a pressing operation, not simply racking. Simple racking can work, if the cane doesn't get clogged, but you lose a fair bit of wine that way.
You usually want to press before the fermentation is totally done, so there is still active yeast to consume the oxygen that might mix in during the press.