It is a two way street.
The US always want free access for US services and freedom to compete in other markets, but is reluctant to open up own markets to free access for others when negotiating trade deals.
As for the TTIP it will become a major stepping stone for US businesses into the world's biggest single market, the EU, and open opportunities for US shipping companies, not just to trade within the EU, but to own and operate ships and shipping companies in EU countries.
EU is not a low labour cost countries stealing jobs by offering low cost goods of inferior quality.
In stead of jobs being lost in the US it opens opportunities for US manufacturer and workers to sell their goods and services freely in all EU countries, an affluent market of 550 mill. people, thus creating jobs in America.
If you are confident in your ability to produce high quality goods and services at competitive prices, what is it you are worried about?
Likewise, US citizens will have the opportunity to work more freely in EU countries, not only those who are highly skilled professionals but anybody who are willing to move and compete on even footing with locals and other migrants.
That means paying taxes of course, but also benefiting from the social welfare system in the country you work or live in.
This applies to Mariners as well, I believe. It is more likely that a well qualified Mariner can find work in the shipping and offshore business. Especially in sailing positions, but also shore based jobs within EU countries.
You may be able to work on EU flag ships anywhere in the world, but still live in the US. The Owners/Managers may save on travel expenses. Especially if the ship is trading in the Americas. In fact this already possible on vessels in "International" registers.
PS> This applies to non-EU countries like Norway, Iceland and Switzerland as well, as they are part of TTIP.