The test is whether the knowledge is of the employer's own product, process or procedure. Deep expertise in marine automation generally, however rare, belongs to the discipline. Command of a proprietary control platform's fault-tolerance logic, acquired inside the company, belongs to the employer and is what the category is for.
The knowledge has to be the company's, not the industry's
Adjudicators see a great many petitions arguing that a talented engineer is hard to replace, and hard to replace is not the standard. What has to be shown is either special knowledge of the petitioning organisation's product, service, equipment, techniques or management and their application in international markets, or an advanced level of knowledge of its processes and procedures. Félix qualifies on the first branch if the platform is genuinely proprietary and his understanding of it goes beyond what any competent integrator could pick up from documentation.
Useful evidence includes design records showing he worked on the fault-tolerance module, commissioning reports in his name across several vessel classes, internal training material he wrote, and a statement of how long the company takes to bring a new specialist to that level. Evidence that undercuts the claim is equally worth anticipating: if the firm has three interchangeable people who could go instead, the petition should explain why they are not going rather than leave the question open.