***Coming next, Export links in "Make a Claim screen" *** The Seafarers Earnings Deduction (seafarers tax) eligibility calculator. SeafarersCalc allows quick and easy checking of voyage dates to determine whether they meet the half-days rule. As the dates are entered, a traffic light indicator shows whether the voyage is valid or invalid. Once a set of valid dates is entered, the eligible voyages go green and you should make a claim.