Prelimnary leg in shipment

Dear Experts

Please provide your views for the following scenario:

My client is haivng a scenario to ship the goods from plant to port & from port to another port. Please let me know whether I can use the single main leg shipment document or I need to create prelimnary leg for plant to port & main leg for port to port.

In case of using main leg alone, please let me know how to capture the movement from plant to port?

Thanks in advance

Ganesh