This form is to be used to notify the Registry of Shipping and Seamen of intent to mortgage.

The notice of mortgage intent is recorded on the register for a period of 30 days, unless it is withdrawn within that time. The notice may be renewed or further renewed for a period of 30 days, by notice in writing to the registry. The relevant fee is required each time.

https://www.gov.uk/government/publications/notice-of-mortgage-intent-msf-4739