hi i will try and help
In exactly the same way is if were on land. As ling as you have an accurate plan and correctly drawn Transfer deed or Lease (and the property is within the boundaries of England or Wales it will be registered with a title number in the same way, subject to the prevailing rights and interests of the area of land/water in question
hope this helps. if it does please leave me positive feedback.The question wont close and you can ask follow up questions if you wish
That I am afraid I don't know as its a rather specialist area. I suspect not if the property is "fixed" into the river/sea bed but a call to the government body that covers UK ship register should clear that up.