Why does the Isle of Wight get 4 tides a day?
Answers:
"Swanage is founded around Swanage Bay, but effectively in the English Channel. The tide is funnelled as it passes round Kent and spread as it moves west to the Isle of Wight where it is 'split' each side of the Isle of Wight. Having so done it 'rejoins' aroundabout the Needles, but since it has covered different distances and been subjected to different sea-floor conditions and depths there is a lag on the north side.
This is a very simplistic explanation, there are many variables that change the tidal pattern around the UK and the rest of the world besides the south coast of England.
There is also loss of tidal energy on the north side of the Isle of Wight courtesy of the Solent. This results in there being a double tide where the leading high starts to drop and is then caught up with by the trailing high.
If for instance you were standing on Swanage beach you would expect the tide to flow up the beach for the high tide, then ebb down the beach for a while and then hover or flow again, although not to such a high point, and then ebb down to the low tide.
Given this sequence of high tide and then a second tide at Swanage, there are places where the sequence is reversed due to different local conditions."
http://www.isleofpurbeck.com/tides.html.