Load cells and weighing multihull builds

Discussion in 'Fiberglass and Composite Boat Building' started by fallguy, Jan 2, 2022.

  1. fallguy
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    fallguy Senior Member

    For some reason, not feeling the best. I do not think I am Covid positive, wife and youngest are positive, but I tested negative, but battling some fatigue.

    This afternoon, I made some spacers.
    The problem I have with my cells is they have no base. Until this afternoon, there were no spacers either. That is the piece above the base that creates room for the bending. The bending moment is the bending of the beam type load cell.

    85CB3288-72F1-4375-9372-6D14652263C5.jpeg
     
  2. fallguy
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    fallguy Senior Member

    By flipping the cells and using them upside down, I can move a flat piece of steel around and place it under things and not worry about balancing everything on the 2" round foot.
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    Either I am still misunderstanding....but....all you need is just something solid under it...anything that is solid.
    Concrete hard standing...1" thick steel.. anything really.
     
  4. fallguy
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    fallguy Senior Member

    The load cell has to be bolted to something. It is not freestanding. The way I am doing it won't require machining the holes.

    By the end of today, I will be weighing something if things go right. Jist not outside. Too cold here. Things, plastics especially, love to shatter at -8F.

    This load cell uses a bending algorithm. The area of the cell at the rubber pad/foot bends; the bolted area does not and the amount of bend provides the weight.

    The RO is not readout, but rated output (voltage). The load cell operates by varying voltage output; then the computer takes that voltage and computes the weight. More weight increases? the voltage.

    Cold weather is also a factor. The cold weather affects the output by 0.0016% per degree C. Not sure how to interpret that well or if that is direct. So, if direct; assuming ambient is 25c, it is -21c here presently. This would be 46 delta. 46•0.0016 is 0.0736%. If the boat weighs 10,000 pounds (God forbid), the error is 7 pounds. Unless I am needing to use another factor for voltage..will check later. I may have that wrong.

    The steelyard charged me 80 bucks for four pieces of 6" c channel torch cut. Heading there shortly.
     
    Last edited: Jan 21, 2022
  5. fallguy
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    fallguy Senior Member

    So, here are some pictures of what I put together.

    all four load cells are mounted foot up on a solid base; checked and each cell registers its own
    968136DB-DE41-4F06-8999-4DC0FC01DE69.jpeg

    here you can see the bending gap
    4097E254-7DC4-40A3-A7F4-9245E68E10DE.jpeg

    this was crudely machined good enough to work; moving the scales will be trouble because everything is connected and the bases are super heavy and cumbersome at 8x12" c channel

    my calibration was limited to what I could lift up to the table saw..when I finished, the scale reads minus 0.6kg; I will modify the setup to no decimal point for boat weights; so that level of accuracy is not even needed
    7203EDCE-E57D-4465-B3C3-1D0450DCE046.jpeg
     
  6. gonzo
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    gonzo Senior Member

    fallguy likes this.
  7. fallguy
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    fallguy Senior Member

    The part that got complicated was that I figured I had to attach them to the hull cradles.

    I like the idea you present, but am too far in to revise the concept now. Even your idea would require welding a flat plat to the top of the jack. They usually come with a floating plate, but not sure I'd trust it to not move sideways.

    Lots of headaches and some sinus crud last nite. Might have the Omicron. Well vaccinated and boosted, though.
     
  8. gonzo
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    gonzo Senior Member

    Those jacks are really cheap. If you have the cells already mounted on a channel, simply lift the channel with two jacks.
     
  9. fallguy
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    fallguy Senior Member

    I can lift the channel with plywood or laminated timber under and use a single jack. Tired of throwing money away.

    Next week is all cold weather; highest for next 7 days is 27F. Not gonna mess with trying to weigh unless we get 35F and sunny. And I need my friend to help. I will update the group after I get some weights.

    Thank you to everyone who contributed. It isn't always one answer or the right answer that helps one trod forward.
     
  10. redreuben
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    redreuben redreuben

    Hey fallguy, Im beginning to regret my suggestion !

    How goes it ? Do you have a weight yet and was it good news ?
     
  11. fallguy
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    fallguy Senior Member

    Too many conflicts. Average temps are like 10F here for the last few weeks. For those who don't know cold weather; things break and men frustrate quickly. So the computer would get tipped over and shatter and the feet would shatter and so we will not wait for a string of days above 35F.

    Church bathroom remodel and dad is dying and I have been holding his hand and helping him go after i got over Covid. Oi vey...
     
  12. fallguy
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    fallguy Senior Member

    Also, @redreuben ..

    I am grateful for the comments you made. If the boat is heavy when the crane comes, I won't know the stand weights and they want to pick them and if the boat is heavy; I can act now better than in 4 months...
     
  13. redreuben
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    redreuben redreuben

    Do we have an outcome ?
     
  14. fallguy
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    fallguy Senior Member

    Yes and No both.

    I did get a weight, but it was very tricky. We had a number of conflicts on weigh day. Buddy was here from up north.

    First, I had failed to extend the wires on the weight feet I made, and that stole an hour to wire extensions to two of the four. Then the fun began. Not.

    we realized I needed a second floor jack, well, so does my friend, so offered to buy a scale for his day of work with me, but that took an hour or more

    Finally, we got the scales under and were all excited to see some weights. Had my friend go stand above one of the four bulkheads with and expected it to go up 180# and nothing happened.. well, talk about terrifying, moments earlier we had a weight? Now it won't count 180#?

    so, I inspect the beam scale....the weighing had bent the top of the c channel base and the beam scale was flat on the surface meaning the thing was on the ground and the weights now reading were bogus too light

    We proceeded to modify the scales and move the beams to the edge of the c channel which worked, but all of this took a lot of time and a lot of jack moving.

    I got some weights, but when I removed each of the two side to side connections and some calcs; it turned out to be over 1000# heavy to starboard which was nonsensical.

    My friend had to get home.

    After he left, the nect day, I realized the starboard side had somehow ended up like 2" higher than port, so the misread was because star side was holding up port side.

    It was a little scary because the one corner of the boat is on a higher grade which means the rest of the boat has to be rather high to be level and my scales are teetering points. So, at one point, the entire boat moved a few inches aft!

    We will weigh it again in a few weeks when we are closer to full completion and I will be real careful to use my level references and also to make sure my teetering is only 3/4" above a landing point.

    I did come up with a number based on the star side being too high.

    So, hull displacement is 8643 pounds. Vessel weight is 7768 no fluids and a few finishing items missing. So, good news for me.

    But really need a final weight with a level boat.

    I forgot to mention at first, the scale say overloaded. That was another hour of recalibration with sand bags...

    in a couple weeks, I'll re-report a cleaner (hopefully) reply
     

  15. fallguy
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    fallguy Senior Member

    Each part of the scale sits under the center aft of the middle of these stands. If I had another $500 to blow, I could setup an individual scale with 4 feet for each corner. But $$$ impractical.
    251F7F24-51C9-4E37-AAE4-D9D4C54A683F.jpeg Getting pretty high up for a single point furniture foot that rotates on a ball. Here it is down on a stack.

    7E984FD5-8F0C-4106-8CC9-2A56095B16D1.jpeg
    But each corner ends up resting on this teetery foot. And the c channel bent in the middle, so the beam scale had to be move to the edges of the channel which meant drilling more half inch holes and remounting.
    8287780D-FC69-4721-9824-33DF70DCEBEF.jpeg
     
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