Only able to travel at 14-15 knots rather than the normal 18 knots
The Ben-my-Chree is currently having to operate its engines at less than half its usual capacity.
It's because of energy efficiency restrictions that have been placed on the vessel.
The treasury minister has been responding to a question in the House of Keys.
Dr Alex Allinson says its hoped the impact on sail times - if it was needed - would be minimal:
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