The Steam Packet is urging travellers to make sure they give the right vehicle measurements when booking.
It says it can't guarantee being able to ship your vehicle if it's bigger than the declared size, though motorbikes are excluded.
A number of vehicles have already been turned away because they've been booked under the wrong size.
The company adds this is especially important on the extra mezzanine deck of the Manannan which is fitted for TT - and measurements include attachments like roof racks, antennae, and bike carriers.
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