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  1. #31
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    Quote Originally Posted by engblom View Post
    SimonLew: Do you have any instructions for how you got the protecting rope around the mast? Did you sew it together, or glue or how did you get it to stay there in a such nice way?

    Now I got a nice idea for how to make a stiff boom that would still look nice: I have access to a plane that can make any shape. I could plane two U-shaped pieces with really thin walls, then reinforce them from the inside with carbon. On the inside it gives a little bit less strength, but any ugly bumps and mistakes will be hidden forever. On the outside it will just look like a nice wood boom. I would probably need to put a glass fibre ribbon on the joints from the outside, when I glue together the two U-shaped pieces.
    engblom, The rope wrap is real simple to do but hard to explain lets see if this makes any sense. You need to use a stretchy line like nylon not a high tech one. The stretch is what make this work well. Start by laying a length of line parallel to the mast (call this the first end) and then wrap the line around the mast back over the first end that is parallel to the mast. Continue wrapping until you have the desired number of wraps. Put a lot of tension on the line while wrapping. Once you are done wrapping tuck the second end of the line under the coils beside the first end of the line that is already under the coils. Since you used stretchy line you can lift up individual colis and keep working the second end of the line under them. Do this until the line is under several coils or if you have the patience work it under all of the coils until it comes out the other end. Use a razor blade to trim the two ends of the line flush with the coils and you are done.

    Your idea for a boom should work. I've seen wood epoxy masts made this way to look like solid wood. Like you said it's less structurally efficient than putting the carbon on the outside but you get the appearance of an all wood boom.
    Simon
    My building and messing about blog:
    http://planingaround.blogspot.com/
    The folks I sail with:
    West Coast Trailer Sailing Squadron

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  3. #32
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    Apr 2008
    Location
    Connecticut, USA
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    An H profile is an I-beam. I-beams have terrible resistance to torsion. I can post pics of 12" steel I-beams which failed catastrophically when torsed.

  4. #33
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    Quote Originally Posted by paulie View Post
    An H profile is an I-beam. I-beams have terrible resistance to torsion. I can post pics of 12" steel I-beams which failed catastrophically when torsed.
    Tru dat. The torsional stiffness of the boom would drop but it may still be enough to work. I'm not rushing out to change the boom. If I get the Goat and my skills so fine tuned that I can percieve the differance of dropping half a kilo of weight from the boom, I'll sign up for the olympic trials
    Simon
    My building and messing about blog:
    http://planingaround.blogspot.com/
    The folks I sail with:
    West Coast Trailer Sailing Squadron

  5. #34
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    'Delaide, Australia
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    Check the WIKI to see data on Bruce experiment trying to make sure really bendy boom stiffer with carbon.

    To cover with carbon makes negligible difference. You need thickness.

    Also remember that a larger cross section is much more powerful at making the boom stiff than the material.

    Finally, construction method you are suggesting.. The most efficient way is to have the carbon fibres in the longitudinal direction. But if all that way the boom will split. Same with a thin wall timber boom. But if you have some of the fibres perpendicular to the wood grin direction it will prevent either carbon or timber from splitting.

    Michael

  6. #35
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    MIK you may have missed my previous post in this forum on my adventures with carbon. I totally agree that increasing depth is the most efficient way to increase stiffness but I added carbon to an existing boom and got a 65% increase in stiffness for a 12% increase in weight. I'm thinking that's a success. Not the most efficient structure but it's now a rock solid boom and it retains the nice look of a slender spar.
    Simon
    My building and messing about blog:
    http://planingaround.blogspot.com/
    The folks I sail with:
    West Coast Trailer Sailing Squadron

  7. #36
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    Aug 2010
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    New Jersey, USA
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    Quote Originally Posted by engblom View Post
    SimonLew: Do you have any instructions for how you got the protecting rope around the mast?...
    Similiar to this:
    Common Whipping | How to make a Common Whipping | Scouting Knots
    Dave
    StorerBoat Builder, Sailor, Enthusiast
    Dave's GIS Chronicles | Dave's Lugs'l Chronicles | Dave's StorerBoat Forum Thread

  8. #37
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    Feb 2011
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    San Diego, CA
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    Quote Originally Posted by paulie View Post
    We'll have to agree to disagree on this one.

    For me, it has very little to do with where I sit when sailing. It has a lot more to do with things like:

    -- where my wife sits when I row. Best if she sits on the floor, leaning against the aft seat, so I can tuck my feet under her knees. For her to be centered, keeping the boat flat, we have to pull the rudder clear of the water.

    -- where the tiller and extension go when tacking. It's really nice to be able to lift the tiller over a head, knee, or whatever else may be in the way at the moment. Sure, maybe that body part shouldn't be in the way. But not everyone who gets on the boat is an experienced sailor. More fun for the uninitiated if you aren't constantly saying "get out of the way" or "sorry about that bruise".

    -- where people sit when they don't want to sit on the floor. I may want to take my mom for a row. She's going to assume that a seat can be used for, well, sitting. And she's not going to want to sit on the sandy, puddly floor. It would be nice to give her room on that rear seat without having to pull the tiller box off. (That's also part of my motivation for moving the traveler further back.)

    My experience with fold-up tillers is all from small boats, not big ones (which tend to have wheels anyway). Small boat cockpits are always crowded. Being able to lift the tiller out of the way makes a huge difference. I've never sailed a small boat that didn't allow the tiller to lift up in some way.
    I pull the rudder blade if I'm going to row for a significant distance. (and the board too obviously). I find that the foils create a noticeable amount of drag. Without the rudder blade the tiller can be bungied to the gunwale out of the way. The other day though, I was sail rowing, and kept the foils working. Then I just bungied the tiller to the traveller like a wrapped python. It was perfect. If I wanted to tweak the helm, a little nudge with my foot set it right.

  9. #38
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    New Hampshire
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    Python reference for the win.

  10. #39
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    Simon, I need some help with the numbers as I don't understand the calculation for the 65% increase in stiffness. I see the 12% difference in weight but can't figure out the improvement in stiffness. I come up with about 38% - which is impressive enough! - and am curious about the calculation.

    Great looking boom, by the way.
    Building Gardens of Fenwick, a Welsford Parthfinder
    Gardens of Fenwick
    Karen Ann, a Storer GIS
    Goat Island Skiff - Sacramento

  11. #40
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    Quote Originally Posted by BobWes View Post
    Simon, I need some help with the numbers as I don't understand the calculation for the 65% increase in stiffness. I see the 12% difference in weight but can't figure out the improvement in stiffness. I come up with about 38% - which is impressive enough! - and am curious about the calculation.

    Great looking boom, by the way.
    Bob, Stiffness (if I'm remembering correctly) is the slope of the load-deflection line so I calculated the slope of the two lines using only the end points no interpolation. Slope for the wood boom is 2.20 and 1.33 for the wood carbon boom. 2.20 is 65% greater than 1.33 ...... OH CRAP that's backwards isn't it. The lower slope is the stiffer one so we need 1.33 is 40% less than 2.20 which is where I assume you got 38% eyeballing the chart. Is that right?
    Simon
    My building and messing about blog:
    http://planingaround.blogspot.com/
    The folks I sail with:
    West Coast Trailer Sailing Squadron

  12. #41
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    Quote Originally Posted by SimonLew View Post
    MIK you may have missed my previous post in this forum on my adventures with carbon. I totally agree that increasing depth is the most efficient way to increase stiffness but I added carbon to an existing boom and got a 65% increase in stiffness for a 12% increase in weight. I'm thinking that's a success. Not the most efficient structure but it's now a rock solid boom and it retains the nice look of a slender spar.
    I did miss that Simon.

    I have a list of goat booms on the WIKI do you have the dimensions of yours and then the amount of carbon you used? The existing data is halfway down this page .. a table for booms.

    WIKI for setting up and tuning Lug and Sprit Rigs | Michael Storer Wooden Boat Plans

    I was referring to Bruce ... who covered a very bendy timber boom with carbon but not enough so it made negligible difference. That data is in the WIKI already.

    MIK

  13. #42
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    Thanks, Simon,

    I did eye-ball it using the data points (roughly 21mm and 13mm) for the 10Kg load, did the math ([a-b]/a) to get the 38%. I'm not savy enough to know stiffness is represented by the slope of the line. I figured there must be a function of the graph representing stiffness but had no idea what it might be.
    Building Gardens of Fenwick, a Welsford Parthfinder
    Gardens of Fenwick
    Karen Ann, a Storer GIS
    Goat Island Skiff - Sacramento

  14. #43
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    Howdy.

    Gosh BobWes, you just made me think of my undergraduate engineering.

    I really only do simple comparisons for my design work.

    Usually because the forces are too uncertain or even indeterminate for the starting inputs for calculation. Plus it gets doubly complicated when the spar itself is tapered.

    But yes. If you start with the forces and locations you can draw a bending moment diagram. Then use calculus in steps to get slope then finally deflection.

    Gosh I'm so rusty. I can barely describe it without feeling uncertain.

    MIK.

  15. #44
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    Quote Originally Posted by Boatmik View Post
    I have a list of goat booms on the WIKI do you have the dimensions of yours and then the amount of carbon you used?
    MIK
    MIK my boom data in a nutshell, blog post has pics and details. This boom is too heavy but I think the same approach can be applied to a lighter wood or ply section with similar stiffness improvement and a lot less weight.

    Douglas fir constant width box section, 37mm wide by 52mm deep tapering to 45mm at the front and 43mm at the back

    Boom is hollow with 12mm side wall thickness and 7mm top and bottom wall thickness

    The carbon was laid into routed channels so the boom has the same exact geometry before and after carbon.

    Carbon tow-epoxy is 4mm thick from tack 1.5m back then 2mm all the way to clew, top and bottom of boom.

    Weights:
    Hollow wood boom: 2815g
    With carbon added: 3150g (wood 2460g, carbon-epoxy 690g)

    Deflections:

    weight | wood | wood-carbon
    10kg | 20.5mm | 13.1mm
    12kg | 24.8mm | 15.5mm
    14kg | 29.0mm | 17.5mm
    Simon
    My building and messing about blog:
    http://planingaround.blogspot.com/
    The folks I sail with:
    West Coast Trailer Sailing Squadron

  16. #45
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    Quote Originally Posted by Boatmik View Post
    Howdy.

    Gosh I'm so rusty. I can barely describe it without feeling uncertain.

    MIK.
    Ha I feel the same way, had to think about this way too much and still got some of it wrong.
    Simon
    My building and messing about blog:
    http://planingaround.blogspot.com/
    The folks I sail with:
    West Coast Trailer Sailing Squadron

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