Carbon Mast/boom Project

Discussion in 'Sailboats' started by BobBill, Oct 13, 2011.

  1. gggGuest
    Joined: Feb 2005
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    gggGuest ...

    But if you do find the stuff in a short enough length and suitably small diameter then the sock can save a lot of work and waste for the first and very last bit of the layup - the 45/45 alighnment fibres that should make up the outermost layer of the layup. The bulk of the fibres should be unidirectional and aligned down the length, but the 45/45 layer keeps it all in column.

    Carbon dinghy spars are fairly frequently built by amateurs over this side of the pond, but its pretty much the most advanced bit of composite construction that's practical without full shop facilities. You do need to be familiar with the materials.

    This is an update of one of the earlier links.
    http://www.uk-cherub.org/doku.php/tech/masts
     
  2. BobBill
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    BobBill Senior Member

    Thanks, gggGuest. Been reviewing that information and saved the link.

    I used similar alignment when I glassed the boat's bottom.

    I think this wee project might be just the ticket for my wee Kite Dinghy, really. Will make it less tippy without the high level weight...
     
  3. Eric Sponberg
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    Eric Sponberg Senior Member

    You are welcome. Glad you liked it.

    Eric
     
  4. outside the box

    outside the box Previous Member

    JFWIW a study on Carbon over Aluminum mast true weight savings.

    This boat is to be equipped with a carbon mast of 17.4 m. At first glance, the weight saved by a carbon mast - is probably only a bit more than 100 kg compared to aluminum - seems negligible compared with the boat's total displacement of 6900 kg. However, as the weight of the mast is positioned high up, it has a long lever with which it exerts a heeling moment. This heeling moment needs to be compensated by the righting moment of the ballast, which has a short lever.

    On the boat in this study for example, the mast is stepped on the deck about 1.4 m above the waterline. Its center of gravity is thus approximately 9.4 m above the waterline: ( 1.4 m + 17.4 m) / 2 = 9.4 m. The keel is 2.5 m deep with much of its weight concentrated down in the bulb. Its center of gravity is roughly 2.4 m under the waterline. For simplicity, we assume that the levers of mast and keel are exerted around a point at the waterline. 100 kg less in the mast means that the heeling moment of the mast is reduced by 9.4 m x 100 kg = 940 m x kg. As the righting moment can be reduced by an equivalent amount, the ballast can be lightened by 940 m x kg / 2.4 m = 391 kg.

    Thus, 100 kg of weight saved in the mast makes the boat in fact at least 100 kg + 391 kg = 491 kg lighter! Furthermore, at equivalent performance, a lighter boat can accommodate a smaller sail area. The mast can then become shorter and lighter. Same for the engine, which can become less powerful and thus lighter. And so forth. Overall, the 100 kg saved in the mast has a potential result in a total weight saving well over half a ton. And that is not negligible anymore!

    Just for what it is worth when thinking beyond the small box most look into.

    Eric please correct any mistakes that may have been made with the study as your input is always found to be valuable.
     

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  5. jim lee
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    jim lee Senior Member

    How about, just thinkin' in text here, molding the mast in port and starboard halves? Then bond them together.

    -jim lee
     
  6. sean9c
    Joined: Jan 2011
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    sean9c Senior Member

    Save 100kg or 220lb? I'm guessing you could do an alum mast with a tube weight under or around 4lb/ft so around 250lb max for the tube. How much do you figure a carbon tube would weigh?
     
  7. rob denney
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    rob denney Senior Member

    Go for it. Your first effort may not be as good as a pro job, but your second could easily be. Let me know the weight and dimensions of the wooden mast and i will give you the carbon layup. Won't be perfect, might break, but one of many cool things with unstayed carbon masts is if they are stiff enough, they should be strong enough. So try it, and if it bends more than the wooden one (either bench or boat test), just add some more carbon.

    Prep the wood mast by taping over the track slot and making sure it tapers in one direction only. Tape (brown packing tape will do) it lengthwise. Lay up a piece of 400 gsm/12 oz db glass cloth with peel ply over it and in the 24mm/1" overlap. When cured peel it off the mandrel. Then put it back on and remove the peel ply.

    Put glue in the overlap, add the lengthwise carbon uni and peel ply and vac bag (very neat) or narrow tape it (time consuming, not such a good job, try to keep the fibres running lengthwise) as tightly as you can, starting from the middle.

    When cured, remove the peel ply and lay up a layer of 400 db on the outside. Add a couple of layers at the mast and boom locations. Slide it off the mandrel. If it won't go, lay up a thicker laminate at the base, glue some pins on and pull it off using your car.

    Do a 1'/300 mm length first. Sock is cool for short pieces, hard work for long ones, no good for vac bagged laminates. And expensive.

    Post cure it and give it a go.

    rob
     
  8. Eric Sponberg
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    Eric Sponberg Senior Member

    Did not check the math per se, but the principle is correct--you reduce weight up high, and that leads to reductions in weight down low for the same stability. Or, you can look at the reduction of weight up high as an increase in stability, which can lead to a redesign of sail area for more power, and faster speed.

    Eric
     
  9. Eric Sponberg
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    Eric Sponberg Senior Member

    There are any number of ways to make masts. I like to keep joints to a minimum. In cases where you need or want a shear web, such as an in-mast roller furler, or a free-standing wingmast, a viable option is to build leading edge/trailing edge sections, each with half the shear web, and join them at the shear web. Or, incorporate the shear web on the TE side, and lap the LE side onto it.

    Eric
     
  10. BobBill
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    BobBill Senior Member

    Making Carbon Spars

    Ferrules or joints are my current quandary...one or two, the latter seems the wiser overall, and how to smooth transition. Not like a fishing rod, which have thread reinforcements around female sections.

    Current plan is to use Force 5 mast pieces due to keeping original bottom aluminum/steel section, depending upon if one or two top sections.
     
  11. outside the box

    outside the box Previous Member

    Thanks as always Eric
     
  12. Jimbo1490
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    Jimbo1490 Senior Member

    This is how you manage socks. Note the simple pulling tool. No handling of the sock is required resulting in no snagging whatsoever. Plastic tubing pulled over the bare mandrel and over each subsequent lamina facilitates drawing the sock over the layup. The plastic is quite easily withdrawn once the sock is in place. Unidirectional sock is in process in the pictures, but the procedure is identical for braided sock. The mast in process is 42' long.




    [​IMG][​IMG]

    Jimbo
     

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  13. Paul B

    Paul B Previous Member

    As a point of reference: The J120 is offered with an alloy rig and a arbon rig. The weight savings of using the carbon rig is reported to be 120 pounds.
     
  14. CatBuilder

    CatBuilder Previous Member

    That is an excellent data point. Thank you.

    Now, what about the cost of an aluminum spar vs a carbon spar of the same strength? Does anyone have data on that?

    I think I read on Eric's site once that they become economically feasible once the boat hits 40' LOA or something. Still, no hard numbers like with this J120 example.
     

  15. jim lee
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    jim lee Senior Member

    Jimbo1490, where did you find those pix?

    -jim lee
     
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