oops, never mind. I just saw further up you already said it.
What is the normal routine you have for contact? You said it wouldn't affect his time but do you mean he gets the same number of hours in total or do you literally mean everything stays the same bar a short ferry ride?
Because the risk here is that you have more losing scenarios than he does. Because of school you need to have Mon-Fri. The courts cannot stop you from moving but they could in theory order midweek contact and that effectively scuppers you. I think it's very unlikely but it's still something to think about.
Do you know the REAL reason he's going to court? Is it the be the noble dad? Financial (ie. costs of ferry)? Or just sheer control freakishness?
I learned a hard lesson when my ex took me to court over our relocation. I couldn't get a straight answer on what she wanted. CAFCASS was a joke. They were dead against me, didn't listen and just kept repeating 'the kids need their mum'. Despite me explaining that I was only the resident parent cos she didn't want to be and that the current routine (which would be unchanged except for a drive) was HER idea....not mine. After that I was shit scared cos all the judge needed to do was order midweek contact and I was screwed. It looked likely and then the ex caved in. Her new demands were less than I originally offered!
Once the dust had settled I realised that what she was actually after was not residence of the children. Even she realised the kids were far better off with me. What she actually needed was a way of showing everyone she had fought the good fight. Someone to blame so people wouldn't gossip about why the kids didn't live with her.
The point I'm trying to make is that people often go to court using arguments which are nothing to do with the fundamental issue. If you can focus on that then you can adapt your strategy to suit.