In my country (Poland), long-haul truckers are paid roughly double what the local truckers (those who get to come home every night) make. This is enough to compensate people for the inconvenience, and there's generally no shortage of workers. So, maybe in your case, there's also some multiplier that would work?
Candidates are definitely attracted to higher pay. The immediate issue is that it takes a long time to get the candidate the seatime, training, and tests to become licensed. We are working on our pipeline. That does not change the shortage today.
The fleet of U.S. flag tugboats as it exists today is running at reduced utilization because there are fewer licensed captains than necessary to operate them. How does increasing pay alone fix that?