What is the ENI?
The ENI (European Number of Identification) is a unique, eight-digit identifier that is assigned to vessels capable of navigating on inland European waters. It is attached to their hull and remains unchanged for as long as these vessels are in service (regardless of changes of ownership or registry).
The first three digits identify the country where the number is assigned (see here) and the last five digits are a serial number.
Every inland waterway craft that requires a Community Certificate (that it meets the ES-TRIN standard), usually 20m or over, should have an ENI. The ENI must be programmed into the boat's AIS equipment.
Where do I get an ENI?
Your ENI should normally be given to you by the body who does your Community Certificate (ES-TRIN) inspection. The EU Directive 2016/1629 Article 18 which defines the ENI says
Unique European vessel identification number
1. Member States shall ensure that each craft is assigned a unique European vessel identification number (ENI), in accordance with Annexes II and V.
2. Each craft shall have only one ENI, which shall remain unchanged during its entire lifetime.
3. When issuing a Union inland navigation certificate, the competent authority shall include the ENI therein.
4. Each Member State shall draw up a list indicating the competent authorities responsible for assigning ENIs and shall notify the Commission thereof, as well as any changes to the list. The Commission shall maintain an up-to-date list of competent authorities on an appropriate website.
"Union inland navigation certificate" here is the Community Certificate under yet another name!
ENI in the UK
As the UK doesn't issue Community Certificates, UK boats needing a Certificate must use a foreign authority, like Register Holland, who are happy to travel to inspect a ship in most countries. They can issue a Dutch ENI to a boat registered in another country, such as the UK, USA, AU, etc. For anyone wanting a UK number for their UK-registered boat, the RYA can issue a UK ENI. The boat must be UK-registered.