If you were to look at a seemingly 'simple' area such as the English Channel, Tidal streams flow one way and then the other, therefore 'in theory' at a Nodal Point the Tidal height remains constant. However this would only be the case if there were no physical features, restrictions in channel widths, harbours or varied depths then this would be the case, which we know it is not.
Due to the water friction caused by the varied depths, channel widths, land features etc the tide is distorted. The areas around Nodal Points can therefore have Double HW's or Double LW's.
An example of an area where this is very apparent is Poole, Dorset which has double HW. Poole Harbour is both close to a Nodal Point but also a standing wave located in the English Channel which causes this. It also means the tidal stream at Poole Harbour entrance ebbs and flows 8 x a day (rather than x 4 like most other areas).
Though the tidal range is relatively small in Poole Harbour (Neap = 0.4m / Spring = 1.5m) it also has to run in and out of a fairly small gap at Poole Harbour entrance which in turn creates strong tidal streams at that location.
For comparison purposes.. a 'normal' tidal curve (in this example at Worthing) the tide rises and falls evenly every 6 hours. Whereas in Poole Harbour the tide rises to HW, falls marginally, then rises again marginally to create a 2nd HW then falls to LW
Firstly, yes, the Mediterranean does have tides though generally of fairly irrelevant sizes when boating.
The tides are limited as the Med is almost landlocked with the inlet from the Atlantic Ocean being fairly small therefore making it almost a huge lake ! Dependant on where you look depends on the information you will gather about the maximum Tidal Range in the Med, but the Maximum Mean Variation seems to be approx 40cm but more often 10 - 15cm (obviously these ranges also fluctuate according to the weather, atmospheric conditions etc).
Looking at Palma de Mallorca, Spain as an example you can see the Tidal range is maximum 20cm in these illustrations: