A coalition of shipowners and industry groups are suing to get the most recent Great Lakes port pilot rates overturned.

The coalition, which includes Canadian bulker owners Fednav and Canfornav, alleges the US Coast Guard used fuzzy math and faulty logic to set rates that will substantially — and unfairly — over-collect pilotage fees.

"The Coast Guard set rates in the Final Rule based on defects in its cost and revenue calculations and supported its decisions with faulty or unexplained logic," the complaint filed in Washington, DC federal court Thursday reads.

According to the lawsuit, the Coast Guard uses a formula designed to meet a revenue target to adequately compensate port pilots. The agency issued new rates effective July.

In the run up to issuing those rates, the coalition says, the Coast Guard used too many working days, included mismatched staffing and volume figures and unfairly added guaranteed overtime to calculate the new rates.

Further, they say the Coast Guard's past formulas have lead to over collection of revenues over the last three full years, including nearly $11m more than the target in 2016. They also want the Coast Guard to come up with a way to credit or refund that money in the new plan.

The Coast Guard declined to comment on the lawsuit, citing a policy not to comment on pending litigation.

The rest of the plaintiffs are Swedish company Brochart, Polska Zegluga Morsak of Poland and Dutch firms Spliethoff Transport and Wagenborg Shipping, plus the Shipping Federation of Canada, the Great Lakes Ports Association and the United States Great Lakes Shipping Association.

In mid-2016, a similar coalition sued over port pilotage rates, seeking a 20.6% reduction in port pilotage rates for the rest of the year.