Load cell in the mast step to measure compression???

Discussion in 'Sailboats' started by Gilbert, Nov 12, 2009.

  1. Gilbert
    Joined: Aug 2004
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    Gilbert Senior Member

    For many years I have been thinking it would be interesting to put a load cell in a mast step to measure the compression load on a sailboat mast while it is sailing.
    Does anyone know if this has been done?
    If so, what were the results compared to the assumptions folks use for calculating compression loads on masts?
     
    Last edited: Nov 12, 2009
  2. gonzo
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    gonzo Senior Member

    They are used, also tension gauges on the rigging
     
  3. Paul B

    Paul B Previous Member

    Can you point to any examples of where they are used?
     
  4. billys maverick
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    billys maverick New Member

    measuring rig loads....

    One of the best resources for rig load measurements, and a great read, is linked below:

    http://www.fh-kiel.de/fileadmin/Data/maschinenwesen/Forschung_Wissenstransfer/Professor_innen/Grabe/Veroeffentlichungen/Grabe_HP-Yacht_02.pdf

    You're going to need a strong loadcell... look in the crash test dummy industry. One company (RA Denton, Inc) builds a nice unit with easy 0-10VDC output which can be acquired with a simple USB Data Acquisition unit (National Instruments has a nice unit for approx $200-300). The Denton loadcell will be expensive, so look around for secondhand components. If you find a good resource, I'd be interested in it.
     
    Last edited: Nov 13, 2009
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  5. Crag Cay
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    Crag Cay Senior Member

  6. Sailwizz
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    Sailwizz New Member

    We have been fitting hydraulic and electronic load sensor on large multihulls of 74ft. It is essential for crew to know the load limits on those heavy cats as there are simply no warning. Linked to load sensor and display sail control, the crew is aware how they are sailing according to manufacturer recommandations. Additionaly, you can have gentle automatic sail releases if the loads reaches the limits set up.
    Check the website:
    http://www.sail-wizz.com/
     
  7. Richard Woods
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    Richard Woods Woods Designs

    I did it in the early 1970's as a engineering student project (before I started my yacht design course) on a dinghy. Coupled to a 2 track tape recorder. One track recorded the sensor loads, the other we used to say "gust coming" "gybing now". Of course that was 10 years before anyone had a PC, we had a mainframe computer we could use but everything was analogue.

    I cannot remember the conclusions, but we had fun sailing around in college time and calling it work

    Richard Woods
     
  8. SukiSolo
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    SukiSolo Senior Member

    For small sailboats I always envisage the thing inverted with the mast bumping on the sea bed in waves......lets you estimate and calculate the structure to be strong enough.

    Done this for real off the UK south coast, mast bent but hull OK. A crude load cell type device might also be to use a thin polymer string sandwiched between a coule of flat plates and determing how wide it spreads, width becomes pressure. Obviously modern load cells are much more suited, as suggested above.
     

  9. Barry
    Joined: Mar 2002
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    Barry Senior Member

    The OP in 2009 asked about just the compression stresses in the mast but did not explain the reason as to why he was wanting the compressive loading information

    Ie there are internal stresses in the mast elements at various positions, tension and compression as there is bending due to the loading of the mast due to the sail attachment forces, compression due to the rigging, horizontal shear resulting from the sail forces, some torsion as the sail forces at the mast will probably not run through the neutral axis, point loading from the boom etc.
    Not to mention loading due to acceleration of the mass of the mast with rolling, pitching or the load changes due to the weight of the mast at different degrees of roll or pitch

    You could measure the resulting compression only loading with a compression load sensor at the bottom of the mast and this would HELP in designing the mast base ? to the boat hull. But this would not be sufficient in determining the stresses within the mast itself.

    You could attach strain gauges to the mast in an unloaded condition, at various height locations as well as radially around the mast in horizontal and vertical orientations to figure out what the mast elements are experiencing when under various wind loadings.
    By mast elements, I am referring to the outer perimeter of the mast at various locations.

    Just a refresher to those without a structural load analysis background.

    There are external loads, say pounds(force), that can act on a structure. These loads can produce internal stresses within the structure, compression, shear,shear flow, tension, torsion, units in pounds per square inch. When the stresses exceed the maximum strength of the material, the structure will fail.

    A simple example would be a solid (short wide) column sitting vertical with a vertical load down in compression. This would be the external load. Internally, most elements will feel stresses in compression and shear.

    Another, a simple horizontal roof truss between two fulcrums, like house walls.
    A uniform snow load will cause compression, shear, tension, shear flow in varying magnitudes at different locations.

    The OP asked for a load sensor to measure the load in pounds at the base of the mast, ie the result of all of the external forces acting on the mast that produce a compression load

    This resulting compression load that he would get from his sensor would not provide enough information to design either the mast cross-sectional shape or the attachment of the base to the hull
     
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