What makes up a good trade convoy?

For all towns (Except river towns) I would suggest having 2 Hulks, 3 Cogs and 3 Crayers.

Hulks are for the transport (No guns on them).

Cogs Are for Transport and Defending (Put all guns on, ship level 1).

Crayers are for defending the Convoy. (Ship level three, Best  guns you can afford on).

Use this convoy with a good trade route that requires a lot of space for the goods, and you got yourself a working goods convoy.