What is the formula for working out high and low tides?

That would be far too complicated for us mere mortals, you could try 'easytide' for on-line tidal predictions anywhere in the world.

http://easytide.ukho.gov.uk/EasyTide/EasyTide/Sele...

To predict earth tidal schedules a lunar day which is 24 hrs and 50 minutes long is used. These extra 50 minutes causes tides to be at different times each day. A lunar day (moon) is the strongest influence on the earths tides. email redbayboats.com and ask for a Tide Table to work out wheather you need to add or subtract for the varies ports.

u can get a time table for tides it will tell u.it has to do with the moon i think it is low tide when the moon is full as it has a greater full on it at this time. hope that is of helpto u

when the water is close then it's high tide

when the water is far away then it's low tide.

You need a tide table - if you search on your nearest port it should come up.

Recommended site:

http://www.wxtide32.com/

Ask the moon