Why am I unable to update the "Chtr Specialist" field?

The Chtr Specialist field in the Voyage Manager is driven by the Voyage Fixture in the Chartering Module.

To modify the Chrtr Specialist field in the Voyage Manager, the Voyage Fixture object rights needs to be given to the user. Having full object rights to the Voyage Manager will not enable a user to update this field since its permission is tied to the Voyage Fixture.