Keel bolt torque procedure.....

Discussion in 'Fiberglass and Composite Boat Building' started by Roly, Nov 10, 2012.

  1. Roly
    Joined: Jul 2005
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    Roly Senior Member

    Do you torque keel bolts up on a new build, loaded, or unloaded, with weight of keel.
    Perhaps, preload supported & final torque unsupported?
    My calculation for torque for 16mm 2205SS was 138 ftLbs- sound reasonable?
     
  2. Petros
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    Petros Senior Member

    It seems to me that you would want to do it unloaded to prevent distortions in the mating surface. You should also support the weight of the hull as much as possible to prevent distortion of the hull shape, particularly along the keel line.

    I do not know what is normal procedure for most yachts but I am an engineer with a lot of experiance with structural design (including aircraft structure). You always want as little distortion of the mating parts as possible. I would also recommend using anti-sieze compound on the threads to get an even torque up, and assist you to remove the keel in the future for service or repairs. As usual, the torque sequence should start from the center and work your way towards the ends, tightening in 3 passes up to the fial torque value.

    The maximum torque value sounds reasonable if the bolts are that size for tensile strength. you also have to verify the clamp-up pressure on the hull materal is not too much. If you crush composite struture you have damaged it before it even has any load on it. Sometimes large diameter bolts are called out to spread the shear loads or clamp up loads over a larger area, not because of tensile strength.
     
  3. Landlubber
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    Landlubber Senior Member

    ....I have always done it on the hard, the yacht sits on the keel anyhow, so that stops any hanging. Torquing in the water to me is wrong.
     
    1 person likes this.
  4. Frosty

    Frosty Previous Member

    A part should be firmly mated with its oponent before torquing down.

    Allignmet etc should have already been checked and there should be no distortion at all not just a little bit or even as little as possible....

    You never pull things or parts up to there position.

    Landlubber has a better way. Its common sense.
     
  5. michael pierzga
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    michael pierzga Senior Member

    For small boats Ive used the torque values listed by the boatbuilder. For a big boat or an unusual keel bolt pattern you might seek additional guidance.

    http://www.waterlinesystems.com/wp-content/uploads/2011/11/KeelBolts.pdf

    Remember the mating surfaces must be perfect or torque means nothing. Bedding into thickened epoxy and mold release works well . Allow the epoxy to set before torquing
     
  6. Roly
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    Roly Senior Member

    Thanks guys,

    This an important step for me and although not intimidated, fully realise the implications of screwing up. (Bad pun.)
    I am a little intimidated , to be truthful!

    I planned to dry fit the keel to make sure all bolts had clearance and then mate with high density filler (one surface with debonding material) for correct mating surface seating/alignment (Plumb). Wait for complete cure. Separate, and then apply sealant (4200), fibreglass or heat shrink elect. tubes around bolts, re-mate, fill around bolts with high density filler and torque to 100ftlbs supporting hull of its own weight & keel resting on terra firma.
    After full cure, lift hull (& keel) clear of ground and re-torque to ultimate target. Then the load tension in bolts of weight of keel will be included in the target torque?

    Any suggestions to procedure gratefully accepted.

    My specs;
    Nut factor = 0.1 (lubed)
    Nominal bolt = 16mm
    2205 2% (heat sheet batch yield Av.) =536Mpa
    2205 Proof (heat sheet) =756Mpa
    Keel wt =1750kg
    Number of bolts = 6 X 2 off axis (75mm off)
    (14 Total) = 2 x 1 on axis fore & aft.
    nuts Bumax A4-100 yield =900Mpa

    Hey michael,
    Thanks for the J-boat site torque specs. My 100ftlbs sounds excessive! Then I am using 2205 instead of vanilla 316?? 48Ftlbs sounds pretty low? I'm leery of crushing floor grid as Petros warned with 138ftlbs as calculated.
     
  7. michael pierzga
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    michael pierzga Senior Member

    Ive always been told that less is best. Don't over torque keels bolt. You will crush the substrate . You can always re torque .

    Always endeavor to evenly spread the load thru all keel bolt...not stress concentration.

    Keel stepping is time consuming . dry fit, square up, mark, modify, re seat in bedding... hope you have a cooperative crane operator !


    Saturdays and a bit of cash seems to help.
     
  8. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Standard Torque formula is:

    T = Sigma x 0.7 x Area x Diameter/5000

    Sigma = Yield or proof stress of material in MPa
    Area = mm^2
    Diameter = mm

    Torque = Nm
     
  9. michael pierzga
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    michael pierzga Senior Member

    Hmmm.........
     
  10. Roly
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    Roly Senior Member

    T = Sigma x 0.7 x Area x Diameter/5000
    =185Nm or 136ftlbs exerting some 8500kg on bolt shank & support structure.
    (Assuming nut factor 0.1)

    Michaels reference above: 5/8 bolt 316 from J22 association =48.5tft lbs (65Nm)

    :confused:

    My support structure (floors and keelson) is 200mm (550kg/m^2 timber encapsulated with 12mm epoxy & e-glass both sides.)
     

  11. Roly
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    Roly Senior Member

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