The US Coast Guard says shipowners notched up another year of strong compliance with port state controls. But the industry appears to be slightly worsening in terms of pollution and fire fighting measures.

The 2017 Port State Control annual report noted that "compliance with international conventions and the safety of shipping has increased dramatically in the last two decades."

As evidence, the report showed the annual detention ratio of ships calling on the US was just under 1% last year, the lowest level recorded, compared to a 1.09% detention ratio last year.

The USCG detained a total of 91 ships last year for safety violations, down from 98 in the previous year. The three-year average rolling detention ratio also decreased to 1.4%, down from 1.6%.

Despite the accolades, the USCG saw an increase in detentions related to fire fighting and fire protection systems for the fourth straight year.

Similarly, the USCG saw an increase in Marpol Annex I deficiencies, which relate to pollution control measures.

Ballast water management violations resulted in USCG issuing 219 deficiencies, double the level seen in the previous year. Rear Admiral John Nadeau warned shipowners that "we are increasing emphasis on BWM compliance and limiting extensions" for installing the kit.

The US Coast Guard also said that the flag states of Belize, Samoa and Taiwan were removed from its targeted list.

The USCG's Qualship21 programme, which rewards owners and flag states for their commitment to safety, saw its biggest one-year jump in enrollment, reaching 2013 foreign flag vessels in 2017, up from 1,493 in 2016. The USCG said ships flagged under France and the Netherlands will now be Qualship21 eligible thanks to the efforts of those administrators to improve their track record.

But flag states including China, Mexico, Philippines and Portugal were dropped from Qualship21 eligibility.