The T&T Express was delayed by four hours this morning, due to a threat made via a telephone call.
The management of the ferry says all 331 passengers were evacuated while checks were made by support services.
The following is a statement by the Trinidad and Tobago Interisland Transportation Company;
"The travelling public is hereby advised that the 6.30am sailing of the T&T Express from Scarborough today (Friday 09 June, 2017) was interrupted due to a telephone message from an anonymous caller advising of a threat to the vessel and its passengers.
The Office of the Prime Minister (OPM) is denying a media report that claimed Prime Minister Dr Keith Rowley was stuck at sea when he travelled to Tobago via the ferry.
The report suggested that the ferry experienced problems while the prime minister was on board.
However, the OPM issued the following statement denying the claim.
"The Trinidad Express has published a story written my Ms Anna Ramdass titled "Rowley stuck at sea, PM sees ferry problems first-hand".
The Port Authority says the T&T Express was forced to turn back because of a problem with the hydraulics for the steering system.
The Port says the boat will sail again at 8pm tonight.
It is apologising for the problems passengers experienced today in the following statement.
"The Authority wishes to advise the travelling public that necessary maintenance works are continuing on the T&T Express and T&T Spirit.
More ferry sailings between Trinidad and Tobago has been cancelled.
The 6.30 sailing from Port-of-Spain was cancelled this morning and the return sailing from Tobago is also cancelled.
The Port Authority said in a statement:
"Tuesday 16th May - the 6.30am sailing from POS and the 4.00pm sailing from TGO have been cancelled due to mechanical issues with the vessel, T&T Express. Any inconvenience caused is regretted."
The T&T Express was taken off service from Friday to Sunday leaving only the T&T Spirit in service.
The Port Authority has says the T&T Express will be taken out of service from today to complete repairs to the Port Inner Main Engine (PIME)
It says that as such, from Friday 12th to Sunday 14th May only the T&T Spirit will service the sea route as follows:
From Scarborough 6.30 am & From POS 4.00 pm
* Passengers with tickets for the 6.30 am sailing on Friday May 12 from POS will be accommodated at 4.00 pm on said date.