If rigid metallic fuel lines are secured to the hull, how must they connect to the engine?

The requirement for connecting rigid metallic fuel lines to the engine with flexible hose sections is primarily based on the need to accommodate movement and vibration in the engine operating environment. Using flexible hose sections that are less than or equal to 4 inches in length allows for some flexibility, which is vital for maintaining a secure connection while minimizing the risk of stress on the rigid lines.

Short flexible sections help absorb vibrations and thermal expansion, which can occur in the engine area. This mitigates potential issues that could arise from a rigid connection that may become loose or damaged due to movement. Such specifications are designed with safety in mind, ensuring that fuel lines can endure the mechanical stresses without compromising the integrity of the fuel system.

Longer flexible hose sections might not only exceed what is necessary to provide adequate movement but could also introduce complexities such as increased resistance to fuel flow, potential for kinking, or failure at the coupling points. The guidelines set forth ensure that a balance is maintained between flexibility and the risk associated with fuel leaks or failures in the fuel supply system.