For Vertical Clearance Problems, heights are given as hight above Mean High Water (MHW). Tide depth is referenced to Mean Lower Low Water (MLLW). Therefore, you must be able to calculate the difference between MLLW and MHW.
To determine Height of MHW above MLLW:
Add one-half of the Mean Range to the Mean Tide level from Table 2 of the tide tables. From the drawing above, you can see that this is an approximation, "ignoring" the difference between MLW and MLLW. This assumes that the difference between MLW and MLLW is typically small.
For the example below (Sneeoosh Pt), Table 2 shows Mean Range is 7.5. Mean Tide Level is 6.42.