Hi Valentin,
I bought the Excursion 5 and also had the same question. I contact the authorities, and NO it is not required to register the boat as long as you don't have a motor. There as been an amendment a couple of years back to the law to remove this length constraint.
However you must not go further than a 150m away from the shore on lakes, otherwise you need to get it registered and have the required equipment (life jackets, etc)
Hope it helps!