carbon fiber wing mast for my cat

Discussion in 'Multihulls' started by rallard, Dec 28, 2008.

  1. Boston

    Boston Previous Member

    anyone tried a CF honeycomb core
    were the honey comb was CF as well

    Im guessing no one tried electrically aligning the epoxy molecules or knows if they are even dipole or not
    although if the matrix is dependent in some way on a random and not a patterned structure then this wouldn't help in the strength anyway
    just throwing ideas out and learning what I can
    B
     
  2. sailor2
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    sailor2 Senior Member

    Like all plastics, the stuff is just one giant molecule, not enourmous amount of separate molecules it is before curing. The curing process means molecules cross link into becoming just one. That is not accounting for secondary bonds of course.
     
  3. Boston

    Boston Previous Member

    [​IMG]

    ok basically looks like this

    that means it is a dipole molecule

    so I looked it up


    Influence of dipole interactions on tensile properties, fracture toughness and glass transition of epoxy resins was investigated by comparing the poly ethylene glycol (PEG) and carboxyl-terminated butadiene acrylonitrile (CTBN) modified epoxy systems. The infrared spectroscopy (IR) spectrums proved that there existed polar interactions between epoxy network and PEG chain. The results showed that dipole interactions played a significant role in influencing on toughness and strength of epoxy resins but had little effect on their glass transition temperature.

    that means at some point in history you guys are going to have a wire matrix embedded in that mold and be zapping that epoxy as it dries for optimum strength without additional brittle tendencies

    actually you could just apply a magnetic field
    same difference I guess
     
  4. rallard
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    rallard Junior Member

    Sailor2, the size of the mast is 205/ 445mm for a thickness/chord ratio of 0.460. Does this mean that the shape could justify the core in this instance? Here is a photo of the bottom while the half mast sections were beeing glued to help you visualize the shape.
     

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  5. Jimbo1490
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    Jimbo1490 Senior Member

    A rotating mast would certainly qualify as one of these exceptions. With a rotating masts of airfoil section, the bigger the better; the larger the mast section, the more the mast/sail combination airfoil behaves as an 'ideal' airfoil. Taken to the extreme, you wind up with a rigid wing sail, which is most efficient of all as a sail, even if it is the biggest PITA on the ocean in terms of sail handling.

    On the project I participated in, the section was substantially larger at ~12 X 24 cm than you'd normally see in a ~12 meter mast, but then it rotated. We had to thicken the section compared to what we could have got away with if the mast was a smaller section.The extra thickness (and weight) was added as an extra biaxial layer. This made the most sense since it was only added to increase the margins against buckling, and there was already more then enough uni material in the mast to support the compressive loads (it was a stayed rig).

    But the rotating spar made the sail performance outstanding (according to independent reviewers :) ), just as it does for the smaller beach cats. The mast was heavier than it would have been had rotation not been a design choice. But that would be true if you built the spar of aluminum as well. The designers considered the extra weight a good trade off for better sail performance.

    Jimbo
     
  6. Eric Sponberg
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    Eric Sponberg Senior Member

    In my opinion, even with a rotating wingmast, a minimum chord is best, and that is the way I design my masts. One of the considerations I always have to answer to a client is "How much wing area is there when the sail is down? I don't want all that mast windage up there when I am under bare poles or when the boat is at anchor or at a mooring."

    I always stress that sail area on the mast itself is at the minimum possible. The mast can be set to the weathervane position in bare-pole situations when under way, although you don't want the mast to weathervane--tie it down. And when at a dock or a mooring, set the mast 45 deg to one side or the other. If two-masted, set one mast 45 deg one way, and the other mast 45 deg the other way, and the boat will sit still in an anchorage or a dock. I have personal first hand experience with this as well as anecdotal evidence from others with these rigs, and it works really well.

    While a rigid wing may indeed be a very efficient sail, it is not necessarily the best in terms of all around usefulness, and that includes reefing. You can't reef a rigid wing. I think that with sailmaking technology and fabrics today, it is relatively easy to make beautifully efficient sails that utilize a minimum mast section. I treat the mast as the leading edge shape to the sail--that first bit of radius that controls the flow over the rest of the sail. Minimum size masts are the best, in my opinion, for all around use and minimum weight and expense to build.

    I will clarify my earlier statement about never using core. I have designed a few masts in which the main structural member of the mast is a carbon fiber structural spar, either round or rectangular shaped, and the leading and trailing edge sections are then built and glued on. These LE and TE sections have been made out of fiberglass and honeycomb core, usually in prepreg. The reason for using fiberglass instead of carbon fiber is because of the relative stiffness. If the LE and TE sections were made out of carbon/honeycomb, they would have a very large ExI stiffness factor and would greatly influence the bend characteristics of the mast (being too stiff). Being so stiff, they would assume a larger share of the load, and strains can easily reach failure levels if not enough carbon is used. With fiberglass/honeycomb skins, on the other hand, the modulus of the glass is very much lower than for carbon, so the ExI stiffness factor is very low. The fiberglass stretches more than the carbon--kind of goes along for the ride without doing much work--and so does not assume much extra load, does not affect bending stiffness that much, and is not easily overstressed. I have used these types of masts on Project Amazon, on Wobegone Daze, on a few multihulls.

    Eric
     
  7. Boston

    Boston Previous Member

    so the CF honeycomb for a core ends up being to stiff and being so obtains little support from the rigging making it more likely to fail ?
     
  8. rallard
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    rallard Junior Member

    Jimbo says "the bigger the better", Eric says "a minimum chord is best".
    Hopefully you are both right, but for different reason. What I think you are saying is that, for performance the bigger will be best but the bigger it is, more of a nuisance it gets when not sailing?
    For my part, I can only speak from the 4 past year experience I had with the wood wingmast on Jolie Julie. The wood wingmast is a bit bigger than the new cf wing mast at 230/480mm thickness/chord ratio of 0.480, the mast has no tapered section at the top end and has one set of spreaders. As previously posted, the new cf wingmast is a bit smaller at 205/445 and 0.460 ratio, has no spreader and the top 8 foot section is tapered to 150/295.
    I absolutely agree with Eric in that he treats the wing mast as "the leading edge to the sail..." it cannot be better said! and that is what makes the whole difference between a standard fixed mast and a rotating wing mast. I also agree that for cruising purposes, the minimum size(provided a reasonable foil shape is retained) will best supply the targetted advantages whilst avoiding the inconveniences.
    It is only the second wing mast I build and I feel I would not feel safe going smaller. My main goal was to save at least 400lbs (especially at the top end)from the former rig and it appears that I will save at least that much.
    The wood wing mast is the first mast I had on Jolie Julie so that I cannot compare the performance against a fixed mast; all I can say is that it worked very well: on a close reach with the mast left straight in neutral position and with approximately 15 knot wind, Jolie Julie sailed at ± 8 to 8.5knots over ground; then just by turning the mast to best position I gained 1 to 1.5 knots and 5 to 8 degrees to windward. Eric does this make sense to you?
    I do not expect that performances will substantially vary with the new mast, hopefully a little better considering the weight saved and less windage? Please make your bets and predictions so we can have fun comparing later.

    On another hand Jolie Julie has been through pretty strong winds like over 70 knots a few times on a mooring and once at anchor, I always leave the mast attached in neutral position and the boat stayed straight as an arrow. I also often had occasions to compare the movements of the boat with other cats with fixed masts at anchor or on mooring and always felt that Jolie Julie moved no more than other boats.
    Eric, I will most certainly try to attach the mast at 45 degrees and see what happens.
     
  9. Jimbo1490
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    Jimbo1490 Senior Member

    I have personal experience with what Eric is talking about, and he's right about the 'windage' problem. It's really more like an unreefable sail problem. Twice I have been caught in a thunderstorm in my small beach cat, a Prindle 19. This is a 170 Kg cat with a 10 m spar and 27 m^2 of sail, so a little wind goes a long way with this boat! So when we got caught in a sudden T-storm (it's a Florida thing; those that lives here knows :D), with no way to avoid it, I moved as quickly as I could to take both sails down and roll them up on the trampoline. But even with both sails down, the boat was making 15-20 kts easily, and flying the hull on just the spar from the storm downburst! This happened twice on the same boat, several years apart. I can only imagine how this might play out on a boat 10X the size in a cramped marina!

    The rest of the time, the rotating wing mast is great fun, though.

    Jimbo
     
  10. rallard
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    rallard Junior Member

    Jimbo, with my wife, I have sailed the coast of Atlantic twice with that boat and mast and we know just about every anchorage place right down to Key West. The thing to do is first to avoid beeing in a cramped marina! During the 2004-2005 season we lived aboard Jolie Julie for 11 months, we have been in a marina only 4 nights, each time to accomodate visiting friends. We always try to get as much room as possible at anchor, although not always possible.
    We have anchored in pretty strong winds, in some occasion for fairly long periods. I can remember a place near Oriental in North Carolina were we had a 2 days storm and I recorded 67 knots and could not see anything outside and had to shout to each other to be heard inside the boat, we had set 2 anchors at abot 45 degrees and barely dragged 30 feet! At one time at anchor in a lagoon accross Atlantic City, for 4 days we had winds over 45 knots with gusts over 55knots.
    When the wind gets stronger the boat simply stops moving around and stays right in line with the wind. Then, I am absolutely convinced that a wing mast with a well shape foil and sufficient chord does sail through strong winds with much less turbulence and drag compared to a standard fixed mast and move less.
     
  11. Eric Sponberg
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    Eric Sponberg Senior Member

    Absolutely, that is exactly the reason for having a wingmast, and you can do that on any point of sail.

    In sailing, you have two rig force resultants to deal with--Lift and Drag. Lift is usually about 5-10 times more powerful than drag. Many sailors and designers concentrate only on the drag portion, trying to reduce it as much as possible. There are always endless discussions on low drag keel and rudder section shape (drag reduction), reducing wetted surface (drag reduction) and reducing weight (drag reduction). But to get the most out of performance, you should concentrate more on improving lift. Simply by turning the mast, you reduced drag at the leading edge certainly, and in the same moment greatly increased lift and gained 1 to 1.5 knots and 5-8 degrees more windward ability. What racing sailor wouldn't give his eye teeth for a performance improvement like that?!?!!!

    I say "simply," but it is more complicated than that--you had to build the wingmast first, and then make it rotate. On a multihull, this is easier to do with wires on the rig, but on a monohull, you really have to get rid of the wires. However, the racing rules say wires are a must. So you have to change the rules--that is going to be a long and drawn out political campaign to make that happen!

    Thanks for the story of your experience.

    Eric
     
  12. Paul B

    Paul B Previous Member

    What racing rules require wires?
     
  13. Eric Sponberg
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    Eric Sponberg Senior Member

    Almost every racing rule of the 20th century, including the Universal, CCA, IOR, and IMS rules. The America's Cup rules including the International 12-metre Rule and the IACC rule require standing rigging. The IRC rule may allow free-standing rigs, but it is anybody's guess how they would be rated. The purveyors of that rule get to decide your fate and may or may not allow it. I am less sure about that one as I do not venture into that arena for boat design. But this is what my colleagues tell me. Another thing that these rules do not allow is rotating masts. And if you want to be competitive with a free-standing rig, you have to have mast rotation. Sometimes the rules will imply standing rigging by setting restrictions on other factors like the maximum size of the mast section which necessarily implies standing rigging is holding it up.

    PHRF does not require standing rigging--your local PHRF racing authorities can rate anything based on your prior performance with your boat. The open class rules for the 50 and 60 classes do not require standing rigging. I am not sure about the 30 and 40 sizes, but I would be surprised if they require standing rigging.

    A stayed rig is probably superior on a closed course because most of the time. Free-standing rigs can be superior in offshore racing. Unfortunately, we never get to see the true competitive differences between stayed and free-standing rigs on closed courses because the free-standing rigs simply don't qualify by the rules.

    Eric
     
  14. Boston

    Boston Previous Member

    never mess with a spooonberg I questioned him on a keel once and was dead wrong :)
     

  15. rallard
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    rallard Junior Member

    ... and here is the undeniable proof that, when at anchor, a wing mast on a cruising cat is a negligible drag factor!
     

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