What's the best transportation to take from Beijing Int'l Airport to Tianjin Xingang?

I plan to go to Tianjin Xingang from Beijing Int'l Airport for my cruise. what's the best transportation to take? Since I'll have a big luggage with me, the walking distance is a big concern to me. I have to arrive the Xingang port before 4:00pm, is the train most reliable on timing? Can anybody tell me about the cost and how often are the schedule of the transportation operate in March?

Thank you very much.