Kurt Hughes Daycharter 36

Discussion in 'Boatbuilding' started by Charly, Mar 10, 2010.

  1. Charly
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    Charly Senior Member

    Headstay fitting& compression tube layout

    Here are some pics of the fitting with some temporary pins in place.

    The square tubes in some of the photos are just there for layout of the compression tube fittings that will go on next. They will be smaller, and will get bushing inserts as well for the pins. It will be kind of tricky to position everything so that the tramp planes out nicely, and more so because I don't have a clear picture yet on how to attach the webbing (I will use "seatbelt strapping" type material) to the compression tubes.

    I've been thinking about how to make the comp tubes. They are about nine feet long each. Seems the simplest way to go about it, and avoid any welding is to cut the tubes to length, find some plate, or flat bar aluminum stock, that is the same id as the tube, make it fit tightly into each end of the tube, stick it down in there a ways and let the "ear"...ie, the end of the flat bar, stick out a few inches, drill a hole, insert bushing, fill in the ends around the bar inside the tube with some epoxy bog, per Gougeon method, and maybe pin it crosswise as well, or maybe just put in a set screw or rivet as insurance to further hold it in place.

    Has anybody else done it that way?
     

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  2. Yobarnacle
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    Yobarnacle Senior Member

    lurking
     
  3. Charly
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    Charly Senior Member

    Compression tubes and Spreaders

    After some bafflement over the plan specs "moments of inertia" the designer set me straight with some dimensions that Online Metals could work with. I have enjoyed ordering and doing business with Online Metals. Their ordering process is user friendly and prompt. (but they don't know nothing bout no moments of inertia :D) Anyway, best choice came out to be 5 inch OD with 1/8" wall tubes.

    Photos show the waste cutoff pieces of the tubes with the 3/4" ''ears" stuck in there like they will go. The tubes will link the main beam with the bow beam. There is really no place for them to go as far as movement (unless a collision) so I am wondering if I really need to weld them in place. wouldn't 5200 work to hold them in there? Then I can close up the ends with epoxy bog etc. I am afraid if I get them welded, something could go wrong with the orientation and they might not fit.

    Custom spreader is mounted on ply pads with thru bolts already bogged in place- so as not to have to perforate the beam.
     

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  4. SamSam
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    SamSam Senior Member

    Are you worried the welder might knock them loose and then they get welded in the wrong position or are you worried about orientating them in the right place to begin with or is there a possibility the positions they are to occupy might change with a change of plans?

    It's probably too late for this, but one way to get a flat surface in 'plane' is to run a tight-stretched string diagonally from each corner so they are like a big X. When the strings just barely touch in the center, the four corners are on one plane. Of course that doesn't position the object level or in relation to anything else, such as the hulls or the waterline, but that can be done with measurements and levels. It is a good way to get the hulls in one plane also.

    Another way to get pretty close is to get way back and eyeball two edges in relation to each other, like in the way you use 'winding sticks' to determine the twist in a wood plank.

    [​IMG]

    My biggest, best tip is that having the ability to raise one eyebrow (like the guy in the photo) is the best bang for the buck around. People will think you know what you're doing, are serious and very intelligent and they can't put one over on you. All superstar actors have the ability.
     
  5. Charly
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    Charly Senior Member

    The vertical orientation needs to match the composite brackets exactly, and they probably vary a degree or two. It is a very tight fit between the two ears of the composite bracket, and difficult to adjust them by sanding. If I have to weld the aluminum part I may get a mobile welder person to come and do it in situ. I could probably mark them with a file or something, but with Murphy's law and all... it would just be so much easier to bond them in there with 5200.


    I can only raise them both together. Like this:
     

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  6. SamSam
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    SamSam Senior Member

    I was thinking you could get everything in place, drill 4 holes through the tubes into the edges of the plate, tap them and then run 4 bolts in to hold them in position. After welding, remove the bolts and weld shut the holes.

    Or just leave the bolts and forget the welding. I don't know what forces they need to handle. Compression I guess, but tension or twisting also?

    http://www.wikihow.com/Lift-One-Eyebrow

    .
     
  7. Charly
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    Charly Senior Member

    Compression on one end of the plate and tension on the other end, with a reversal on occasional uplift, as in a slamming sea. Don't know about the twisting, but it seems it would be miniscule.

    The thing about leaving in the bolts is the galvanic corrosion problem.

    Hey Sam Sam, the new splash target date now is around Columbus Day, after the storm season peak. I should be able to make that one without too much frantic running around.
     
  8. Charly
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    Charly Senior Member

    If I had this to do over I would let the gap be a bit sloppier, go ahead and weld up or fabricate whatever aluminum piece need to go in between there then come back after fitting and parge in some structural bog, after waxing the aluminum part up. This would give a perfect fit with less fuss.

    Live and learn
     
  9. SamSam
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    SamSam Senior Member

    I'm pretty sure 5200 wouldn't work in that situation and it sounds like welding is what's needed. How about the idea of temporarily bolting, then when done welding, removing the bolts and welding the holes shut?

    I believe I sent you a PM, but I'm not sure. I hit a button and it disappeared anyways.
     
  10. Charly
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    Charly Senior Member

    Sounds like the best option. I could then move them about without worrying about misalignment.

    PM sent
     
  11. SamSam
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    SamSam Senior Member

    You could take the plates into a machine shop and have them surfaced thinner pretty easily while they are loose. No idea of the cost, but it would be an easy, simple thing to do for any machine shop.
     
  12. SamSam
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    SamSam Senior Member

    You could take the plates into a machine shop and have them surfaced thinner pretty easily while they are loose. No idea of the cost, but it would be an easy, simple thing to do for any machine shop.

    I wonder though about access to parge in bog, and how easy that would be to do in a thin, deep slot..?
     
  13. Charly
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    Charly Senior Member

    could be done in either case.
    How best to prep the inside of the tube for welding before fastening the ears ? Just degrease and sand? does it need "tooth" like when bonding wood?
     
  14. SamSam
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    SamSam Senior Member

    I don't know. I'd leave it to the welder. It's aluminum so there are special preps for it, it might be it has to be welded right away so oxides don't re-appear. I'd google it so you get an idea of what's needed and then ask your welder what he's going to do so you get an idea of whether he's a getrdun kind of guy or someone who might do better than that.

    I don't understand what "could be done in either case" means.
     

  15. Yobarnacle
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    Yobarnacle Senior Member

    Maybe you could find slightly smaller tube (or round bar) that would just insert inside the compression tube. Half moon slices of the smaller tube could be welded to the ears, in a vice. Simple welds when not internal. Then the ears with their new round profile could be epoxied, bolted riveted in the compression tube. Or welded if you insist.
    Drill staggered holes, just a few in the compression tube ends. When you insert the rounded ears, they close off the holes from the inside. You can now simple weld the outer tube hole to the inner tube exposed in the hole.
    Any strength loss from the holes drilled, is more than compensated for by the extra wall thickness you added with the inner tube/ear construct.
     
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