What is a backbone?
A backbone is something that can help you if you are getting raid ~ For example if you feel like your fleets are in danger from getting plundered then all you have to do is go to the warehouse where your back bone is type in the number you want to sell from warehouse then click "sell from warehouse". No turns needed ~ Just a certain amount of turns. Then your ships will take longer to be plundered...
Who can use Back Bones?
Anyone can use Back Bones ~ Particularly people with trade fleets , In my opinion you should not have a backbone until you have at least 10 trade fleets - Even then your backbone will only be level 25... So then you can have 5 trade fleets storing goods, whilst the other 5 is making cash ~ So this will not be affecting your gold supply by a huge mass amount.
Or you can just have a level one warehouse with just 500 gold bars in you would earn more and a less of a cost : You would be able to fill it in 25 hours...
How to get a Backbone?
It is quite simple, just get a level 25 warehouse and set up a trade fleet ~ Lets say your level 25 warehouse is Tzogos then port 1 you would choose " Tortuga " : "Buy only from Market" Then Port 2 "Tzogos" :Buy only from market then below the list should be " Store in port 1,2,3,4" Click number 2 then assign the chosen fleet... Then you are done the fleet will keep on going back and fourth storing tools then once its full it will be a normal profitable trade