Put the summary of the bug you're having here
What I expected to happen was...:
...for boats to float.
What actually happened was...:
...they sank to bottom of swamp/ocean.
Steps to Reproduce:
1. Put a boat (Birch) out into the water and it sank to bottom.
2. Tried another type of boat (Oak) same result. It sank.
3. ...
Environment
System Windows 10. Using Java Edition snapshot.
Linked issues
Comments 2
If my previous comment explains your problem, this is a duplicate of MC-130475
Can Confirm. Though the problem is not that the boat can't float; the problem is that the boat gets placed too deep underwater. The boat itself can float just fine, but only if you place it on a solid surface, then drive the boat into water to get a properly functioning boat.