Dozens of vessels were waiting Tuesday to clear the meticulous inspection process required under the Turkey and UN-backed accord aimed at easing fears of a global food crisis.
Some vessels spend days at anchor for a procedure that officials said they were trying to speed up, amid growing desperation among some crews to get through.
On board the Barbados-flagged black-and-white Nord Vind ship, the relief was palpable when a team of inspectors arrived.
One of the boat's Syrian sailors said the crew had been waiting for eleven days.
"It's too much," said Marwan, who declined to give his full name.
Despite views on the landmark Hagia Sophia mosque and historic Sultanahmet district, "the anchorage area is difficult. We must constantly change places and restart the motors... Why are we waiting like this?" he said.
Since the deal between Russia and Ukraine came into force on August 1, more than 6.9 million tons of grain have left for Europe, the Middle East and to a lesser extent, Africa, according to data from the Joint Coordination Center (JCC) overseeing the agreement.
Massive Daily Costs
When Russia invaded Ukraine in February, there were fears of a global food crisis. The agreement allowing Ukrainian grain exports has brought much-needed relief.
The downside however are the delays on either side of the Bosphorus Strait, the busy maritime passage that allows onward passage from Ukraine's Black Sea ports to the rest of the world.
Under the terms of the deal, ships must be inspected entering and leaving the Black Sea.
The JCC itself raised the alarm over the delays last week, reporting the backlog build despite increasing the number of inspection teams from two to four.
The group noted last week the waiting time for cargo ships leaving Ukraine reached nine days on average, in a statement that warned of "congestion" in some of the waters near Istanbul.
Shipping companies were angry, complaining about delays that cost them "$5,000 a day, plus a loss of earnings", said a local source who spoke on condition of anonymity.
But, as debate renews over extending the deal by November 19, the JCC has urged ships to prepare for inspections before declaring they are ready for a check.
"On more than 50 occasions, inspections could not be completed at the first attempt due to the lack of readiness of the vessel," it said.
'Ships' Lack Of Readiness'
Each team has eight inspectors: two for each of the parties to the agreement, which is to say Russia, Ukraine, the UN, and Turkey, mainly responsible for logistics.
The process, which can take hours, involves several procedures.
The ships' cargo must be fumigated with a pesticide to protect the grain from various infestations, said Udani Perera, a UN inspector from the Sri Lankan navy.
On one ship, inspectors had to disembark before returning to the vessel as the hold's doors had been left open, putting their health at risk.
Once on board the Nord Vind, the inspectors divided up the tasks: checking logbooks, identity papers, the route, fuel tanks and the state of the grain.
Perera also had to check there were no unauthorised individuals on board.
Her Ukrainian colleagues checked the fuel gauge, while the Russian inspectors walked along the gangways and carried out tests in the hold.
Perera said an inspection could take an hour, depending on the vessel's size and the crew's preparation.
But on Tuesday morning, one empty 225-metre (740-feet) Singapore-flagged ship, had to wait more than three hours during its inspection before it was allowed to proceed to its destination near the Ukrainian port of Odessa.
"This morning it took a little more time because they were missing some documentation," Perera said.
But it was good news for the Nord Vind.
After a two-hour inspection of the 169-metre (555-foot) long ship, carrying 27,250 tonnes of wheat, it got the green light to travel to Tunisia.