The bug

Fishing line is blocked from rendering inside of a boat.

This is not MC-198777, as it concerns the line not being connected to the held item; this ticket concerns the boat blocking the fishing line from rendering entirely.

How to reproduce

There are many ways to see this issue in action. One example:

1. Place a boat on land
2. Cast a fishing rod at a lower piece of land
3. Observe the fishing line in third person

Expected results

The length of fishing line inside of the boat would be visible.

Actual results

It is not.