Why was the adaptation of existing marine propellers ineffective for early aviation attempts?

Marine propellers were engineered for water, which is a much denser medium than air.

Propellers designed for marine environments are optimized to displace water, a fluid with significantly higher density and viscosity than air. When these designs were applied to aerial craft, they failed because the aerodynamic requirements for moving through a thin medium like air differ fundamentally from the requirements for moving through a dense medium like water. The mechanical properties and fluid dynamics at play in water do not translate to flight, leading to ineffective thrust generation and drag, which hindered early inventors before the development of dedicated aeronautical engineering principles.