Folding system loads

Discussion in 'Multihulls' started by tamas, Nov 11, 2013.

  1. hump101
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    hump101 Senior Member

    It's not a problem. I'm travelling for the next few days, so won't be online much, but will have a few hours to look at this. Imperial measurements are fine, I'm happy to work in whatever you are more comfortable with, I'll just convert them.
     
  2. bruceb
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    bruceb Senior Member

    Crooked drills and lazy operators

    Thanks H!
    When the drill press table is off by a couple of degrees and the operator allows the drill to drift a millimeter or two on four sets of holes, some errors will occur. Maybe about 5-6mm total. In defense, the press is over 40 years old and the operator somewhat more. Just saying.:(
    Once I have made some adjustments, I will try to do better. Maybe.
    B
     
  3. hump101
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    hump101 Senior Member

    Model images

    Bruce, here are a few images of your model. I've gone with a solid model for the braces, and tried a range of element definitions. The beam is using area elements to reduce computational requirements, since I don't have any information on it anyway I've just left it as a structure to allow load input. I'm modelling the connection to the centre hull with boundary conditions.

    The model as-is contains a few simplifications that I will develop once the geometry is confirmed. I've put the pins through the centre of the 5x3 box, as it should not clash according to my cad, but you will need to check clearance on the centre hull and the beam to ensure such an arrangement can pivot without catching something.

    Any comments appreciated. I'll run a few test cases with this geometry before updating.
     

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  4. bruceb
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    bruceb Senior Member

    Real progress

    That is very nice H, and is exactly what I expected. I am visiting my boat today to recheck some measurements, and I will go over everything tonight. I will report back as soon as possible so you can finish this.
    Thanks again, Bruce
     
  5. hump101
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    hump101 Senior Member

    No problem. I have to say that, after looking at this, I am not sure I would design a folding system like this if it were my boat. You have four pivots to do the job of two, and three structures to do the job of two, so it is a redundant, and hence heavy solution. On top of which the height of the system when folded is much more than is necessary. Not an issue with small tri's, but not ideal as they get bigger.

    Having said that, it is simple to engineer, and will function even with crude engineering, so there are positives.
     
  6. warwick
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    warwick Senior Member

    I think when Ian Farrier was working the system early on, It was over engineered. because of the new approach at the time and for customer confidence. Now it has/is being refind, reducing the redundancy of the system.
     
  7. bruceb
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    bruceb Senior Member

    12' x 12'

    H, I totally agree, this is complex and heavy. My estimate is around 150 lbs per corner- 100 lbs for the fiberglass beam (Ray's estimate), and the rest in arms, pivots and attachment bracket. Maybe a little more. The original system is about 125 lbs a corner, so this is heavier, but folding, not "dismounting", is is well worth the weight penalty. That does not mean I like it, I am really trying hard to get some weight out of the boat, not add it.
    I have a basement full of discarded folding systems/arms/beams from messing with my B-24 and this boat, but this is the only one I got to really work for the 33, and it was also from a trusted and tested source. I am certainly open to any changes/improvements/total redesign that would be simpler and better.
    At least as I see my design restrictions, the mounting points and deck/cabin overhang are fixed, so I can't use a long F-style lower strut. The whole boat is built around the upper beams, and they are not practical to change. I need the boat to fold to less than 12' wide and 12' high for transport, and less than about 14' wide for in the water docking. The mast rides at about 12' on the trailer, so the upper end of the folded beam has to be less than 4' above the upper pivot for the same overall height. The top of the beam, folded, (in the current design), has to be less than 17" horizontal from the upper pivot and the float can't stick out farther to stay under 12'. Of course, the float can't go down too much below the waterline as it folds. I am not willing to invest in exotic materials for this old of a boat, but I think the current design built in "normal" materials will be well worth the price and effort. A simpler/lighter design would be wonderful:cool:
    Bruce
     
  8. bruceb
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    bruceb Senior Member

    alternates

    W, I agree, the current F-fold is fine and certainly well proven, but it won't fit my boat without extreme modifications to the boat. Mine is built in foam/glass, so it is even more difficult to change than if it were a plywood boat. I would really like this to be an almost "bolt-on" mod, so if anyone else wanted to up date a B-33, it would be possible. We have different storage issues here in the US than most other places in the world, so folding adds a great deal to the usefulness of a tri. In my local area, along with many other areas, the only launching options for a wide boat are trailers or a crane. When I get in the water, I will have the largest sailing multihull on the lake, even though we have 50' sailboats and powered houseboats over 100'.
    B
     
  9. warwick
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    warwick Senior Member

    Bruce I think you are doing a great servicce for ther trimaran owners, I wsh you the best of luck.

    The Malcom Tennant syph is 28 foot, may be combining ideas, I have been thinking of a lower strut with a cable restrainer to stop it going down too far.With a mounting pad and pivot mount/bracket. That way he end of the cross beam and inboard end of the swing arm become the anchour points

    sylph2.jpg
     

    Attached Files:

    Last edited: Dec 18, 2013
  10. bruceb
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    bruceb Senior Member

    maybe

    W, Thanks for the support, I hope I can add something to the collective folding knowledge. The second drawing does have possibilities, I will have to scale it up and see what happens. I think when I tried that, the float was too tall to tuck in under the wing, so I had to angle it. The float is about 40" tall at the forward beam, 30" wide, and even deeper at 50%, plus some of the beam sticks out/up, and the overhang is only 24" so quite a lot sticks out. The main hull is about 50" at the waterline, and I have to be less than 144" total. It would be close, but maybe possible. I do like the pivot right down at the bottom of the wing as it makes the pivot support structure easier to build.
    I have not managed to find a set of plans for the B-33, so I have to take measurements off my boat while it is on the trailer. With everything loaded as close as it is, I can't trust all my numbers. I hope to remove the floats from the trailer sometime in the next week, and that will give much better access.
    H still thinks I can eliminate the upper arm, or at least make it non structural, and this plan would do it if everything clears. If the upper arm is out of the way, I can seat the inner beam end against the cross pipe much like a Farrier.
    At this point, I have not cut anything off the boat that wasn't made to be removed, but once I cut into the ends of the crossbeams, I will be committed to the changes. I would much rather make the mistakes on paper.
    Bruce
     
  11. hump101
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    hump101 Senior Member

    Designing the boat from scratch, I would use a double hinged beam with a single coupled folding controller, but I am not sure how practical this would be on your boat, given your overall beam constraints and fixed existing cabin width.

    Your current proposal is functional, and simple to make, and if the weight is really an issue, then make it in carbon, or both in alloy. In any case, you can't eliminate the upper arm in this design. You could eliminate the inboard portion of the beam if you allow the two arms to contact each other and be locked together in the unfolded position, and this would then reduce the height in the folded position. The arms inboard pivots points would need adjusting, and the arms themselves would need to be strengthened.
     
  12. ChineTri
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    ChineTri Junior Member

    Hi Bruce, Hump,
    Thanks for this discussion, I learned a lot.
    I have a question concerning the pivot points in the arms. A while ago I took some pictures of the lower pivot point of an F-22. This pivot is made of a stainless steel pin of about 16 mm (5/8"), surrounded by a tube of what I think is fiberglass with thickness 1 mm. Around that is a bushing of nylon or some other plastic also about 1 mm thickness.
    In this discussion I haven't found anything about similar construction of the pivot point.

    What would be the use of these extra layers? Will you fit the ss pins directly through the holes in the aluminum arms/hinge points? Can fiberglass and nylon withstand the compression forces?
    JP
     
  13. hump101
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    hump101 Senior Member

    I can't remember where this was previously discussed. It appears that the thin inserts act as lubricant/gap fillers only, not as conventional bushes, since although they may deform under maximum load, they never have to rotate under any significant load. As such, you can get away with a softer bush material than if you required the bush to rotate whilst under maximum load. Complete failure of the bush will not lead to a failure of the joint, just a small amount of play in the joint.

    Personally I would prefer to use thick walled stainless or composite tube for the pivot. Lighter and stiffer than bar, and the increased diameter reduces stress on the bush.
     
  14. bruceb
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    bruceb Senior Member

    More options

    H, (and everybody else), you have convinced me to at least try for a better solution. So far, its not working very well, but I do have some new ideas to try. I will try to post in a day or so, but this is a very busy time of the year for me and it may take a little longer. If I use a "Farrier" style lower arm attached to the lower stainless tab, with the upper arm non load bearing, the lower arm and beam position work fine, but I am still having trouble with the upper arm design. I can't move the upper pivot inboard as the cabin is in the way, and it also interferes with the beam/crossbeam compression pad area. I will draw it as I get closer to a working solution.
    Happy holidays,
    B
     

  15. hump101
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    hump101 Senior Member

    No problem Bruce, I will run this model anyway now it is generated, to see how the numbers work out with the material specified. It will give us a baseline for comparison with any other design you want to look at.
     
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