Part 1 of the UK Ship register is a full title register. This means that it is necessary to submit evidence of ownership of the vessel, stretching back at least 5 years in the case of a pleasure yacht, in order to prove that the person seeking to register the vessel is the legal owner of that vessel. Once a vessel is registered on Part 1 of the UK Ship Register a mortgage can be registered against the vessel.
Part 3 (also known as the Small Ship Register) is not a title register. It is not necessary to submit any evidence of ownership of the vessel in order to obtain a SSR certificate. Mortgages cannot be registered against a vessel on the SSR. The SSR certificate will however be sufficient to satisfy foreign authorities if the vessel is taken out of UK territorial waters.