Basic Bubbling Edit
A bubble is a convoy of vehicles travelling along the same route. The outer vehicles are empty, protecting the higher value items in the centre. E.g.
V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11
If V1 to V11 are vehicles, the high value items could be placed in V6. Pirates / highwaymen attacking from either end of the “bubble” would not hit your center vehicle and its precious cargo. This would therefore prevent them from pillaging V6.
Another tactic is to fill the bubbles with worthless items (1g starter items) so when a pirate attacks, it will get filled up with worthless items and a full Pirate / Highwayman is not able to take items from any other defeated vehicles.
Advanced Bubbling Edit
The more protected the item in the middle is, the less likely it is to be stolen. A method of adding extra protection is to send empty vehicles from the destination city, like so.
The bubble containing the item will get additional front protection from the destination city vehicles initially, and when they pass they will act as a rear blockade too.