The random encounters I think must be based on a predetermined amount of “steps” taken. I noticed that if I rewound the game and changed direction, I’d have a random encounter regardless after the same amount of spots moved. However, I had one span where I crossed from one port to the other without a single encounter. Actually, I came VERY close to making two full passes. Also, it’s worth noting that if Jaws was close by when a different random encounter happens, he’ll probably show up anyway.