Memorial Bridge in background.

Moran Towing maintains at least three and often four tugs in Portsmouth to assist with river traffic that brings several million tons of cargo a year - coal, natural gas, road salt, and products for a Foreign Trade Zone - up the the Piscataqua River and through Portsmouth Harbor.

It can be a challenging job. While deep and ice-free, the Piscataqua is also the third-fastest tidal river in North America and extremely narrow by shipping standards.

As a result, the tugs operate only at "slack tide," periods of about an hour twice a day when the incoming tide temporarily balances the outgoing current of the river.