In the app: Account → Delete account, then confirm with your password. Otherwise write to the contact at the bottom of this page from your account's email address.
After the request the account is disabled at once. For 7 days you can change your mind: sign in again and the request is cancelled. After 7 days the deletion is final.
What is deleted: the account (email, password, language), consents, boats, favorites and folders, routes, reports with their votes and confirmations, devices registered for notifications, the shared position, exported archives. Only one line of the account operations log remains, without email or other personal data, kept for 12 months.
Before deleting you can download your data from Account → Export my data. During the beta Knotly sends no email: you will not get a confirmation by mail. The data is kept on a server in the European Union.