Ok just a few tips I have picked up while playing the game, hopefully some other will add to the list 
1. Diamond, Gold and alike dont weigh much and they are close to home ports being on the west of Africa, best to use a fast ship that will turn around profits quickly and outrun pirates than a heavy ship as you can hold as much as you want as the trade item is so light.

1. Diamond, Gold and alike dont weigh much and they are close to home ports being on the west of Africa, best to use a fast ship that will turn around profits quickly and outrun pirates than a heavy ship as you can hold as much as you want as the trade item is so light.