As the UK is no longer an EU member state, UK vessels should expect greater scrutiny when arriving in Holland and tighter limitations on their welcome there. Certain ports are designated ports of entry although pleasure boats arriving elsewhere can in certain circumstances make use of a derogation which allows them to register with the local authorities and their arrival will be reported.
At IJmuiden boats can report their arrival at the Koninklijk Marechaussee on the quay by the lock into the Noordzee canal. Reporting your departure is done in the same way and there is some flexibility to allow for changes of plan due to weather conditions. Check reporting requirements here.
As UK citizens no longer enjoy the EU right to free movement we can only travel to countries in the Schengen area for up to 90 days in any 180 day period. Use one of the Schengen calculator tools to check your stay.