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  1. #16
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    If everyone is happy I will have a look through the boom discussion and move it to a different thread .. I think it is pretty discrete from the rest of the discussion and it is certainly important enough.

    MIK

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  3. #17
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    Apr 2008
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    Connecticut, USA
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    Warm Beer,

    Thank you for corroborating my tunings so far. (General tuning thread here https://www.woodworkforums.com/f169/g...4/index13.html) I believe that Christophe has his traveler in the same spot, so that makes 3 of us. I might try moving it back to the transom again, just to see if it helps balancing the helm as Woodeneye suggests, but I'm pretty happy with it where it is.

    I have tried restricting the play in the traveler on calmer days. I think it helps a bit. Not enough data points to be sure yet. More study needed there.

    I should mention that I have also ditched the battens. I think everyone has.

    I have not yet shackled my throat to the yard. It's the next change, I think. I do notice that I can bend my yard a bit when yanking on the downhaul, so there is a LOT of tension along the head.

    Woodeneye,

    Thanks for all the tips! As I said above, I may try moving the traveler back to the transom again. Maybe I'm not losing as much leech tension as I thought. Worth another look-see.

    I will definitely try moving the downhaul back to act more as a vang. It was on my list of experiments but got forgotten somehow. I'll let you know what I find.

    You are probably correct about the "stayed boom". I was thinking more about catastrophic failure and the need to sail wearing protective gear. But I'm more likely just to hang myself!

  4. #18
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  5. #19
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    Jul 2011
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    Default Strength of boom and yard.

    As there is an on-topic thread for boom, I am asking here:

    Do boom and yard need to have the same stiffness vertically? For example if the boom is 60 mm thick, should the yard also be 60 mm? I mean, will a stronger boom make the yard bend if both are not having the same thickness?

  6. #20
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    We are just discussing that in General.

    The original spars are drawn with about the same maximum diameter, but the loads are distributed differently because of the way the forces are introduced.

    The yard is restrained only at one point - the halyard. So that is the widest point (highest bending moment) and either end can be tapered towards the ends (lower bending moment.

    But the boom is a different case ... it is restrained at three places. Pulled down at the downhaul, and the two places the mainsheet blocks are placed ... one midpoint and one at the end.

    This means the bending moment only reduces down to zero between the downhaul and boom front and between the back of the sheeting and the tip. So the boom has to be a more constant diameter for more of its length.

    I wouldn't get too caught up in worrying about the ideal setup unless you are a good sailor already and want to get the maximum out of the boat.

    The standard spars do give good performance.

    There is not real relationship between sizes of boom and yard because they have quite different functions.

    The yard should be aerodynamically "smooth"ish but the boom can be very fat because the wind does't really cross it .. its pointing into the wind most of the time so has a small cross section as the wind sees it.

    So some have gone for a slightly larger yard.

    And a number are playing with very fat and deep hollow booms.

    But remember the boat sails very well with the standard parts.

    MIK

    I'll post later what I have sent to Clint about some calcs for the boom.

  7. #21
    Join Date
    Apr 2008
    Location
    Connecticut, USA
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    I agree with MIK that the standard rig -- right out of the plans -- is fine. I've been sailing with it for a year now and I am nowhere near getting all of the performance out of it that a good sailor would.

    Yes, I have dreams of making all kinds of modifications: building a stiffer boom and unlacing the foot of the sail; locking the throat so it does not slide down the yard; rigging some sort of boom vang to control sail twist; blah, blah, blah.

    But right now, the only substantive change I've made is to give it a really hardcore 6:1 downhaul. All the other changes I've made to the rigging have been for my convenience when setting up the boat or sailing it, not really for performance. (To summarize: I ditched the full-length battens, moved the traveler further aft, and got rid of the "square lashing" between boom and mast. I also made the outhaul adjustable, but that's of limited value with the lashed foot and I haven't played with it much anyway.) And I'm using a sail that is really not optimized for performance either.

    Yet, with my current set-up, I can still go faster than a lot of the "racing dinghies" in my area. Other sailors smile at my quaint rig and then their mouths hang open when they see me do 5 knots in 7 knots of wind. I love that look on their faces!

    So, get your boat built and don't worry about tweaking the rig just yet. There will be time for that later.

    (There is one other change to the plans which is arguably more important to make right away than building a fancy box boom, a change I intend to make soon and wish I had made right from the start: modify the tiller so that it flips up. Maybe Clint can post pictures of how he did his. It won't give the boat any better performance, but the convenience is enormous.)

  8. #22
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    That can be an after market add on.

    It's really hard stopping people from sitting on the back tank when sailing already! )

    Its interesting how images of big boats influence owners of small boats that they need to steer from the back too.

    The reality is for all boats they should be as far forward of the tiller as reasonably possible.

    Hehe
    MIK

  9. #23
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    Apr 2008
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    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.

  10. #24
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    Jul 2011
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    Finland
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    I have actually an idea for what is maybe a very simple improvement: How about attaching to the mast, a bit down from where the boom should be, an eye for the downhaul to loop through. This will make boom to stay better in place if you are not lashing it to the mast...

  11. #25
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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.
    Sorry ... I am a really disappointing person

    I agree with you. But I'll keep pressure on people to build the boat the simple way and use the original rig. It is more about psychology.

    You already know where to sit!!!

    MIK

  12. #26
    Join Date
    Feb 2011
    Location
    San Diego, CA
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    I picked up a 12 foot section of this stuff - contoured DF, 58 mm x 38 mm to check bend and weight against my existing 40 mm round Spruce boom:
    http://www.homedepot.com/buy/f499-11...ing-50181.html

    Here is the data. I think I found my new boom. In reality, the coutour is flatter than the profile picture, and I chose the lightest piece with nice grain.
    Some may call it sacrilege, being an off the shelf, already countoured boom, but heck, it's exactly what I'm looking for, with very nice stiffness!

    --------------------------------weight----------------------bend with 10kg (22 lbs)
    old boom (round spruce)--------1.9 kg (4.1 lbs)---------------50 mm
    new boom (oval DF)------------3.2 kg (7.0 lbs)---------------10 mm

    center hung weight, with the spar supported at 1 foot from each end

    Checking the tuning wiki, these numbers make sense

  13. #27
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    Jul 2008
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    Florida USA
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    Finally getting around to writing up my boom adventures and this thread looks like the place to do it. This post is an abbreviated version of the detailed writeup on my blog.

    I started out with a solid Douglas fir constant width box section, 37mm wide by 52mm deep tapering to 45mm at the front and 43mm at the back. It was too flexible and heavy, so I routed out some wood from the middle to form a fat U shape and capped it with another piece of Douglas fir. This increased the vertical dimension of the boom and lowered the weight slightly but the boom was still much too flexible. Then I decided to test adding carbon to an existing boom.

    I routed 2mm channels full length top and bottom of the boom and increased the depth of the channels to 4mm for about the forward 1.5m of the boom. I did this since the max load is at the downhaul. Carbon tow was then laid into the channels. I used tow because it is very inexpensive if you shop around. There is only a few $ of carbon in this boom, certainly under $10.

    The weights of the boom variants:

    Hollow wood boom: 2815g
    After routing carbon channels: 2460g
    With carbon added: 3150g


    I very carefully measured the deflection of the hollow wood boom before and after the carbon was added using a bucket and water as weight. The chart below shows deflection vs. weight of the boom before and after carbon.



    For a weight increase of 335g or 12% the stiffness increased 65%! The boom now feels indestructible and no deflection is noticeable under sailing loads. The boom is heavier than I'd like but that is mainly because I believe there is too much wood left. The 690g of carbon and epoxy is doing most of the work and a lot of the wood is just along for the ride. A thinner wall wood box with the same amount of carbon would most probably work just as well. How much thinner could it be? I don't know.

    The boom with carbon laminate.



    This is the carbon reinforced boom with 14kg load:



    And the finished unit:
    Simon
    My building and messing about blog:
    http://planingaround.blogspot.com/
    The folks I sail with:
    West Coast Trailer Sailing Squadron

  14. #28
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    New Jersey, USA
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    Great write-up and (as usual) great craftsmanship.

    I wonder if the top layer of carbon is doing any work? The carbon tow is resisting tension; is the top of the boom under tension? That might be a place to save weight if it doesn't. Also, you might be able to rout out the sides without sacrificing vertical stiffness. Not sure how much weight that would remove, but you'd have a cool I-beam boom.
    Dave
    StorerBoat Builder, Sailor, Enthusiast
    Dave's GIS Chronicles | Dave's Lugs'l Chronicles | Dave's StorerBoat Forum Thread

  15. #29
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    Jul 2011
    Location
    Finland
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    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.

  16. #30
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    Quote Originally Posted by davlafont View Post
    I wonder if the top layer of carbon is doing any work? The carbon tow is resisting tension; is the top of the boom under tension? That might be a place to save weight if it doesn't. Also, you might be able to rout out the sides without sacrificing vertical stiffness. Not sure how much weight that would remove, but you'd have a cool I-beam boom.
    Dave, the top surface of the boom is in compression. There is a misconception out there that carbon-epoxy composite does not do anything in compression. It can carry a compressive load just fine it's just that it is much stronger in tension. For example a free standing all carbon mast bends under load and has tensile stress on one side and equal compressive stress on the other side of the tube. In that case the carbon-epoxy is carrying a big load in compression. It is possible to design asymetric structures to minimize the weight but that's more clever than I'm up for. I'm sure with proper engineering my boom would weigh 1/3-1/2 of what it does now but I was trying to see if slapping some carbon on an existing wooden boom was worth the effort.

    Removing wood to get an H profile sounds pretty cool, wonder if the weight removed would make any performance differance.
    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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