If you can attach a vertical support component to the dock, i.e. a long fiberglass or wooden pole then you've got your starting point, and if you use heavy wire like 10 gauge stranded, that should act as the additional guying support for the vertical's stability, and then you'll need two more supports for the ends.
If your dock is not particularly strong you might consider a weighted support on the ocean floor under the dock for the vertical mast, and then use a sliding coupler attached to the side of the dock if you have the type that floats up and down with the tide changes.......if not, then just make a permanent attachment dockside, and you've already got two support points secured before you string the wires out to the sides which will give you the 3rd and 4th supports. The downside is that remember that when you use a larger wire size, the sag of the wire will increase, and the point is: that the higher your vertical supports are the better off you will be. However, the only one that is crucial is the center support because you can always direct the ends downward in an inverted v configuration, which will probably be an advantage to you anyway because most of the guys working 160 are more vertically oriented than horizontal. So if you do it that way your two end supports won't have to be very long at all, which means that guying them will be much easier.......you might even be able to just dig a hole in the sand for each of them and use some quick set concrete as their bases. 73's and good luck, Ron email@example.com