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Thread: Deck Mounted Winch - Force, Stress,

  1. #1
    Associate Engineer
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    Sep 2019
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    Deck Mounted Winch - Force, Stress,

    Hi all,

    I'm trying to determine how many bolts are needed to mount a winch to the deck of a boat.

    The problem:
    A winch will be mounted to the deck of a boat using the 2'x2' spacing with 1"-8 bolts. The winch has four feet (one in each corner) that elevates it off of the deck. These feet can be directly bolted to the deck, or the can be modified/replaced with new feet to meet the loading requirements. The new feet can be plates that span the length or width of the winch, to whatever dimensions necessary. The loading of the winch is currently unknown but an assumption of 2500lbs can be made. The loading is subject to directional change (alpha in the picture) and can also change in height based on the quantity of rope on the spool. The weight of the winch itself is unknown but an assumption of 5000lbs can be made. The quantity of bolts needed is unknown and is dependent on the total loading.
    (See picture for diagram)
    Hopefully this is a clear enough description, let me know if anything isn't clear.

    I'm not asking for this to be designed for me (unless you really want to ) but I do need some guidance on how to approach this.

    I plan to start with a FBD and determine the loads on the current four feet through a static analysis. From this point, I am a bit stuck as I'm not sure what the next step to take is in determining the quantity of bolts, or if needed, how to design a plate to bolt onto the deck that will have the required quantity of bolts to accept the load.


    Please let me know your thoughts.

    Thanks,
    AK
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  2. #2
    Administrator Kelly Bramble's Avatar
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    Feb 2011
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    Bold Springs, GA
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    A "winch" or a "Windlass"? You'll want quality Stainless Steel bolts fresh or salt water. Determine what the "winch" installation specification are and do that..

    You can do the 2D statics loading calculations analysis here: https://www.engineersedge.com/calcul...d-modeling.htm

    Also, I would consider the deck loading capability as well. You may need a backing plate to distribute the load and honestly, 2000 # seems excessive unless you has a serious need for something.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Associate Engineer
    Join Date
    Sep 2019
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    Winch is correct.

    Thanks for linking that load calculator.

    Unfortunately the specifications are not available. The winch is over 20 years old and the manufacturer is no longer in business.
    Upon looking at it further, with the predrilled holes on the deck being 2'x2', the current feet don't align so custom feet will need to be fabricated. I am trying to determine what this plate needs to be with regards to thickness and how many bolts are needed to successfully distribute the load.

  4. #4
    Associate Engineer
    Join Date
    Sep 2019
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    Quote Originally Posted by Kelly Bramble View Post
    You can do the 2D statics loading calculations analysis here: https://www.engineersedge.com/calcul...d-modeling.htm
    Looks like I need premium membership to access the modeler. Not sure if it would work for me but can't test it out without the membership.

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