In general, most ferries are quite safe, especially on popular UK and Irish routes like those between Scotland and Northern Ireland. Bikes are typically stored in a specific area with other bicycles and secured by ferry staff. That said, bringing a lightweight lock for peace of mind isn’t a bad idea, particularly if you’re the type who worries about theft or damage. A simple cable lock adds very little weight but can provide reassurance.
However, if you find yourself feeling anxious about leaving your bike unsecured, it might be more than just a one-off concern. In that case, you could benefit from fear therapy or anxiety counselling, which is available in Belfast and throughout Northern Ireland. Cognitive Behavioural Therapy (CBT), for instance, can be very effective for addressing fear-related responses, whether about theft, safety, or travel.
Also, it might be worth looking into travel insurance that covers bikes specifically. Some UK-based providers, such as CycleGuard, Pedalsure, or even British Cycling membership, offer bike theft and damage coverage during travel, including ferry trips. This can provide added peace of mind without needing to lug heavy locks around.