What are the six types of vibration in a 2-stroke engine?

flowchart TD
    A[2-stroke engine] --> B[Unbalanced inertial forces]
    A --> C[Firing forces/moments]
    B --> D[Axial vibration]
    B --> E[Transverse vibration]
    B --> F[Vertical vibration]
    C --> G[Torsional vibration]
    C --> H[Longitudinal vibration]
    C --> I[Horizontal vibration]

• Types: axial, transverse, vertical, torsional, longitudinal, horizontal
• Source of excitation: unbalanced inertial forces and firing forces/moments from reciprocating masses
• 2-stroke vs 4-stroke: 2-stroke has half the firing harmonics of a 4-stroke
• Concern: low-speed 2-stroke propulsion engines more likely to excite hull natural frequencies
• Instrument: IACS Rec 167; DSC Code cha-9 §9.4.1