Maximum heights can vary by ferry operator, from 4m up to 5.2m. We would recommend clarifying for any height over approximately 4.2m.
In terms of width or length there is no theoretical maximum, however, anything over 18.5m long and 2.6m wide is considered abnormal. Ferry companies will always require prior notification of these loads, and may require an approval prior to shipment. Axel spacings and weights can be a determining factor.
Weight limits are determined by the limitations of the ports you are travelling to and from. Any loads over 50 tonnes total weight will require prior approval.