Why is my Ironclad not healing?

[Siptah]

So I'm playing a game as England at the moment on an Island Plates map. I built lots of royal navy dockyards and so my great admiral points are going through the roof. I'm at the start of Renaissance era, but managed to get the GA that gives a free Ironclad already. So I retired him immediately to get that sweet 60 strength unit (including 1 free promotion) right away. I conquered two cities with it and now I have the problem, that I can't heal it anywhere (it's down to 5 HP). It is in my territory, of course. I've also put it on a royal navy dockyard, I tried making peace. But still: the 'fortify until healed' button is not possible to press and sleeping doesn't heal it. Why is that? Because I don't have coal that I would need to build Ironclads?
On a related topic: do these free units that you get from GPs benefit from the faster XP generations of harbors and encampments?

 

[Aenthin]

You need at least one of the required resources to heal them, in this case, coal. This applies to all units with a required resource.

 

[Siptah]

Thanks, I thought this would be the reason, but was not sure. So I need to beeline to coal, but then the Ironclad won't be that OP anymore...

 

[bladex]

lol i love that GA

 

[RawlsRorty]

Thanks, I thought this would be the reason, but was not sure. So I need to beeline to coal, but then the Ironclad won't be that OP anymore...

I'm pretty sure you can still heal by pillaging fishing boats.

 

[TurboJ]

In addition to coal you also need the tech to build ironclads to be able to heal it (if somehow you manage to get coal without the tech).