If you use the /ride command to summon an Enderdragon in a Minecart or a Boat you can't kill him with strength 255. He will turn red if you try it.
MCPE-105902
Can't kill Enderdragon in Minecarts/Boats
Resolved
Duplicate
1
The issue isn't the boat, it's that strength 255 is not functional. See MCPE-20469.
You might want to try strength 20.