Holding Down Bolts And Chocks In Marine Engines

Holding Down Bolts And Chocks In Marine Engines
         Marine Engine is a massive structure so its very important to securely fix the engine into the ship hull. The floor where main engine is situated is strengthened by additional bars and griders. The bedplate which is the base of the engine is attached to the tanktop by holding down bolts and chocks. 
Functions Of Holding Down Bolts 
> Fix the engine in correct position with good alignment so that there will not be any uneven load on bearings, transmission shaft and stern tube.
> Provide a clamping force, so that the friction between bedplate, chock, and ship’s structure resists the propeller thrust.
> Strengthen the stiffness of the engine

       Chocks In Marine Engines    
              Bedplate is mounted on the chock and is attached to the tanktop by holding down bolts. It make proper contact with the surfaces and dampen the vibration transmitted from Engine to the bedplate.

Types of Chocks,
 Based on the purpose there are 3 types of chocks, support chock, side chocks and end chocks. 
   > Support chocks: These are the main chocks fitted beneath the bedplate as shown in the fig above.
   > Side chocks: Side chocks are in the side of the frame, inline with the main bearing
   > End chocks: End chocks are at the  end of the frame, two in numbers

 Based on the material there are three types, chocks Cast steel Chock, Resin Chocks And Resilient Chocks

     > Cast Steel Chocks 
               Cast steel chocks blocks are individually hand fitted, so installation requires  expertise and it is time consuming. So these types of chocks are not preferred in modern marine engines.

     > Resin chocks Or Epoxy Resins chocks 
                Modern marine engine makers recommend epoxy resin chocks because of its easy to use and is of low cost. At the time of installation, liquid resin mixture is poured in to the work area so its very easy to apply and get 100% surface contact.
    Installing procedure for resin chocks
             > Clean the work area and tank top for dirt and oil
             > Make liquid resin by mixing hardener with resin proportionally 
             > Prepare the temporary dam so that liquid resin gets contained in the specified area
             > Insert the holding down bolts in the hole drilled with releasing agent applied on bolts
             > Pour resin mixture into the temporary dam around the inserted bolt. 
             > Tighten the holding down bolts after cure period is completed.
   Advantage of Resin chocks, Why it is used in marine engines?
              > Less skill and cheaper to install
              > Maximum surface contact
              > It is non corrosive
              > No chemical reaction

    > Resilient Chocks
            Resilient chocks consist of number of flexible rubber vertical mounts, mainly used in auxiliary engines. These type of resins are used in small and lighter engines like auxiliary engines. Because of heavy weight and higher forces, it is not used in 2 stroke marine engines 

If You Know More or Have Doubts Please Comment Below.


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  1. what is the proceduress check the tightness of the holding down bolt. what is the duration

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