Tidal Diamonds

Tidal diamonds are invaluable sources of information in relation to the speed and direction of tidal streams.  Whilst away on a paddling trip recently I came across, what must be an almost unique diamond?  It is diamond C on Admiralty Chart 808, East Guernsey, Herm and Sark.
49°27.5 N
2°31.4 W
Hours
Dir
Rate (kn)
  Sp           Np
-6
-5
-4
-3
-2
-1
HW
+1
+2
+3
+4
+5
+6
213
213
213
213
033
033
033
033
033
033
213
213
213
5.1            2.2
4.1            1.8
2.7            1.2
1.2            0.5
1.2            0.5
3.9            1.7
5.2                  2.2
 4.9            2.1
 3.3            1.4
 1.5            0.5
 1.3            0.5
 4.0            1.7
 5.2            2.2
The first observation is that the streams only flow in two directions, exactly opposite each other.  The tide is flowing approximately SSW and then it changes abruptly and goes NNE.  An exact 180° change.
Something else to note is that maximum rate occurs at high and low water, with slack, if it can be called that, occurring at mid tide.  Many a sea paddler or other water user has been caught unawares because they assume that maximum rate must occur at mid tide and have set out on what they thought was high water slack.
The advice is to always double check your data and to keep your eyes open for interesting and possibly unique items of information as shown by this tidal diamond.

 

Brehon Tower in the Little Russel with Herm Island behind.  The tidal diamond is located just to the left of the tower.