If you have 35' at high tide and 80' of chain that's only a little more than a 2:1 scope so I wouldn't reduce your chain length. Maybe you could increase the size of your top chain so it goes down more vertically. That way your boat would rub against the ball but the chain might miss the hull.
You could also accomplish this by adding a weight to your balls anchor chain,
which should hold it in a more verticle position. Also, boats tend to tether better from a bow eye than from on-deck fittings.