An easy fix could be if you bring the CV too close to the shore it runs aground. Then once this happens, you can't move it again for a period of time.
Add a prompt when setting the CV cource that says something like "Cource runs perilusly close to land. Running aground is possible, proceed?" and then an arena message along the lines of "vAdmiral Has Run TG34 Aground! High tide in 20 minutes." and you got a winner.
I haven't been in the Terrain Editor for a while, but if the terrain was made where the water around the actual land was made "shallow" out to a certain distance by using the water depth settings, would that prevent a CV group from getting "too close to shore"?
Your idea then being that the CV has to keep a certain distance, but the shoreline for LVTs, PTs, etc. to forward spawn at is still at an acessable ditance from the town?