Salary vs Day Rate & Extra Work Days

I am working overseas on a foreign flagged vessel for a American company. Several of us have had to workover on our time off . The problem is: Most of us work day for day on salary ,when we workover the company pays us the extra day Salary divided by 365 days not 182.5 days. We have argued and tried to explain it they refuse to listen and keep saying we are getting our extra days pay and thats that. Things are kind of tight now so none of us want to quit or get fired . Has anyone dealt with this and have any suggestions on what to do .