There is a forumula - try the official forums.
I'm not sure if tides have a monthly cycle or just a daily one, so it may be that your question is pointless.
In any event, a simple (but admittedly tedious) experiment trying all the possibilities will
a) provide the answer
b) bring you a few hours nearer death
In my opinion any activity which can simultaneously satisfy both of these criteria while contemporaneously providing a modicum of pleasure is worthwhile of sympathetic consideration.