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.
These repairs have impacted on the normal sailing schedule, and have resulted in the T&T Spirit being completely withdrawn from service to undertake repairs to its third engine.
These repairs are expected to be completed by Sunday 28th May, and the vessel will resume operations on Monday 29th May at 6.30 am.
As such, the T&T Express will be the only vessel in operation during the period.
The public is advised that T&T Express is delayed from 2.00 pm to 8.00 pm later today.
The vessel developed problems with the hydraulics for the steering system, about twenty minutes into the sailing to Tobago, and was forced to return to the POS Ferry Terminal for repairs.
The repairs are expected to be completed by 7.00 pm, following which the vessel will prepare to make the journey to Tobago at 8.00 pm.
The Authority regrets any inconvenience that may be caused by the disruption in today’s sailing.
The decisions taken were necessary to ensure that our passengers and crew are safe during the voyage."