Originally posted by squashplayer1:

I have searched everything. The places where I landed the boat there were no materials left.

If there had been the materials, I would have rebuilt the boat, of course.

In other cases, the materials were there.

I suspect that the boat was pulled to the sea by the wind maybe.

The boat can't move once you are off it. Mobs destroyed your boat. The other times you found your materials is because they hadn't despawned yet.
All items will despawn after a bit if they are not in the radius of a worktable.