The company started taking reservations on Monday, June 1, and by 6.30pm more than 8,800 passengers had been booked to travel.
The number of bookings is substantially higher than the same day in 2014, which was in itself a record.
The number of motorcycles booked increased from 3,452 to 4,621, and the number of other vehicles, including cars and vans, increased from 935 to 1,277.
Online bookings were up 80% on last year, with almost 1,800 made through www.steam-packet.com, while 1,520 reservations were made by phone or in person.
The Steam Packet Company Reservations Office and phone lines were fully staffed throughout the day, with extra staff brought in to help deal with the
Staff handled 1,037 calls, 13% more than the equivalent day in 2014 and more than double the number of calls handled on a normal Monday.
Isle of Man Steam Packet Company Chief Executive Mark Woodward said: “I would like to pay tribute to all our staff who worked flat out throughout the day to assist as many TT fans as possible to secure their travel for the 2016 TT.
“We experienced an increase in bookings of 33% compared with the same time last year, which is testament to the continued growth in popularity of the TT.
“We have also invested heavily in the removable mezzanine deck on Manannan which is helping to meet increased demand for space for motorcycles in particular.
“Due to the extremely high level of inquiries, I appreciate there will have been frustration for some customers who could not immediately get through on the phone or experienced delays online.
“By bringing in additional staff where possible and by investing in making our online booking system more robust we have made considerable steps forward in meeting demand.
Despite the high demand, some places on sailings to the Isle of Man during the 2016 TT sill remain. Checking online or with the reservations team for further details.