FCDO advice including information on permitted duration of stay and visas for Italy: www.gov.uk/foreign-travel-advice/italy
For information on the validity of RYA certificates abroad see Evidence of Competence Abroad.
Evidence of competence is required (although seldom inspected). Italy has not adopted Resolution 40 but for a UK flagged vessel an ICC (valid for the vessel concerned) is generally acceptable and is recommended.
Italian translations of many RYA certificates and their related course syllabus are available from the RYA website. www.rya.org.uk/go/translations
EU member state (part of the customs territory of the EU (which includes territorial waters)). Further information is provided on the Entry & Exit Formalities page under Customs - EU Member States.
Part of the Schengen area.
As part of the customs territory of the EU (which includes territorial waters) and the Schengen area customs and immigration checks may not always be required on arrival and departure.
Italian translation of your insurance document from your insurer. This is a document which is specific to Italy. It indicates that you have the required liability insurance in place. This document must include the serial number for any tender and or outboard the vessel is equipped with. It is recommended that you check that you have the correct documentation with your insurer prior to going to Italy, to avoid a fine.
If you are considering visiting Venice and intending to explore the canals using your dinghy, be aware that boats with engines over 10hp are required to have temporary number plates, issued by the City of Venice (which are valid for no longer than 30 days).
The number plates can be obtained by completing a form which includes providing details of all the potential skippers and information about the boat. Photocopies of valid identity documents for all applicants are also required together with a payment.
Procedure for applying for temporary number plates (in Italian)
Form to apply for temporary number plates (in Italian)