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Requirements of bedplate

1. 1. 1. 1. 1. Strength- able to withstand force without failure
            2. Rigid- enough to support engine weight and maintain crankshaft alignment, yet flexible to accommodate hog and sag of ship
            3. Lightness- strength to weight ratio, less load on foundation, reduce cost
            4. Toughness- measure of resilience and strength, withstand fatigue stress
            5. Simple design- easy maintenance, saving cost
            6. Access- ease of inspection and maintenance
            7. Compact- giving room for engine room space
            8. Bedplate consist of 2 longitudinal girders and many transverse girders.

Longitudinal gives longitudinal strength, transverse gives transverse strength

Longitudinal

• Double plate is more stiff but design more complicated, and difficult to access holding down bolt.
• Single plate is popular with modern engine.

Transverse

• Provide stiffness to withstand firing load without bending, which damage the bearing pocket,
• Double plate give high strength and stiffness, hole In plate for inspection, which is stiffen by tube to restore strength.

Bedplate material 

• Prefabricated steel (light, easy to manufacture and repair but distortion and cracks due to welding.
• Cast iron (good vibration damping, reduce cracks, but difficult repairs) 
• Hybrid. ( mild steel for longitudinal, cast steel for transverse)

Causes of cracks

• 1. Excessive vibration
  2. Slack tie bolts
  3. Overloading due to bearing wear 
  4. Poor welding, stress relieving
  5. Stress riser (concentration ) on weld

Repairs for mild/ cast steel

1. 1. Cracks to be chipped and weld, not to distort welded part
   2. Use ductile electrode which deposit close to parent metal

Repairs for cast iron

1. 1. 1. 1. 1. Stop the crack by drilling hole near crack
            2. Metal lock 

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