THE SHIP PROB. RMVX HELP NEEDED A FAST AS YOU CAN

lets get in detail ... i have created a map with ocean tile in it , i want my player for example ship to move
on it normally.
(Yeah i know that theres a vehicle but when the vehicle moves on water it doesn't encounters random
enemies... help what can i do)
thanxxx in advance

thanx Fallen-Griever But I Want only one enemy so can i do like this

Set Variable "Random Encounter": Random 1-50
If "Random Encounter" = 1 Then
Start Battle: Monster Group 1
End
would this work or will it encounter any problem with gameplay
(Thanx for your efforts and fast reply)