The carriers do have a height above the waterline of 206ft in sea-going trim and the Forth bridges have clearances of around 144ft (road) and 150ft (rail). While this would appear to restrict their cruising on the River Forth to as far upstream as Grangemouth (they are too wide to escape by the Forth and Clyde Canal), the designers took this problem into account during the design and construction.
The main mast which bears a significant amount of the radar and radio antennae is 62ft high and can be lowered by hydraulics.
This, along with choosing an appropriate low tide, should allow them to leave for their home port of Portsmouth and return to use the dry dock for refitting.
What is of more concern is the expensive dredging in Portsmouth Harbour which is needed to let them enter without grounding and to turn when arriving or leaving their berth.
This is also adding to the cost of a type of craft whose day of strategic use has passed.
Bruce D Skivington
Gairloch, Wester Ross