Was it a jammer or a frequency scanner? There is/was a scanner (I had one) that checked to see if anyone else was on that frequency before running, Tower sold them. It's a small black box a little larger than a pack of cigarettes than has lights that will scan the frequency.
If you do believe that it is indeed a jammer then they can be reported to the FCC.
Now, if these guys were real jerks, they could have found that channels you were running on and changed their crystals to the same as yours and interfered with the running of your boats.