If you wait until March 7th and call Steam Packet prompt at 8:30am they resell any tickets where the prepaid deposits were not fully paid for, there are usually some tickets available for each ferry.
Here are the numbers;
(by phone on 0044 (0) 8722 992 992/0044 (0) 1624 661 661 or online at http://www.steam-packet.com.
I have a ticket 1 bike/rider for 8/06/16 10am return 11/06/16 at 5.30 from Haysham saved seats if that's any good, just needs to reimburse the deposit and pay for the ticket if that's any good
, also throw in 1x grandstand ticket for senior day, no good to me. Kev