carbon fiber wing mast for my cat

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

  1. Paul B

    Paul B Previous Member

    Universal and CCA rules were obsolete 40 years ago, and probably didn't mention freestanding rigs because it would have been unheard of due to materials limitations at the time.

    IOR never required standing rigging and had no limits on section size. Regardless, it has been gone for almost 20 years.

    There was at least one IMS boat (Jaun K's Krazy Kyote II) that had a freestanding mast.

    IRC rates boats with freestanding rigs.

    There was nothing in the MORC rule to require rigging. In fact you would receive rating credits for larger mast dimensions.

    I'd have to check, but I believe there are limits regarding section dimensions in the 12 metre class rules (must pass through one ring, but not another), but as far as I know nothing requires standing rigging. Who cares, that class has been gone for 20+ years.

    I believe there is something similar in the current ACC class. This class does forbid rotating or "twisting" masts.

    The Open classes allow freestanding and rotating rigs.

    What I do know is Ben and Eric Hall built a rotating wingmast for a J90. It wasn't as quick as a standard rig.
  2. Paul B

    Paul B Previous Member

    Maybe you don't have the same knowledge base I have...
  3. Boston

    Boston Previous Member

    probably not
    but I read these threads religiously and although I may not comment often I have developed a lot of respect for his opinion
    Ive also noticed that he and a few others ( few being the key term ) are willing to admit when they have erred or reciprocate graciously in kind
    a trait that is unfortunately lacking on a few other threads that will remain unnamed

    cheers mate
    I was just joking around with it so no worries
  4. Eric Sponberg
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    Eric Sponberg Senior Member

    You asked which rating rules--you did not specify if they were current or not. I tried to show some evolution of rules over at least 100 years.

    Free-standing rigs have been around since apes first fell from the trees and took to rafts. The first rig most likely was a tree-trunk stuck in a raft and hung with tree branches or hides. I do not have proof of this of course, just thinking logically. Read my article on my website about the state of the art of free-standing masts, and you'll get a fuller description.

    IOR Rule 802.6: "Forestay and Shrouds. To qualify for measurement under this rule, a yacht must be fitted with a bona-fide fore stay."

    This wording is duplicated in IMS Rule 203.7.

    Of course, once you fit a rig with a fore stay, you really need to have a back stay to stabilize the rig. And if you are conscientious about reducing size and weight aloft and competing with other stayed rig boats around the buoys, you are going to rig like them. As I said, a free-standing rig may not be competitive in round-the-buoys racing.

    Also, the wording of these rules regarding the measurements of the rig necessarily uses the standing rigging as measurement points, thereby implying standing rigging.

    IOR Rule 802.3: "Rotating masts are excluded for yachts measured under this rule."

    Again, this wording is duplicated in IMS Rule 203.6.

    Krazy Kyote's mast was not free-standing. It had stays, and it's innovative feature was that it twisted, and technically it did not rotate in the normal sense of the word. Therefore, it took benefit of a loophole in the wording of the IMS rule. Twisting the mast achieved very nearly the same effect as rotating, but twisting was not dis-allowed, therefore it was allowed.

    The Twelve Meter Rule (specifically, rule #23) is written with the implication that standing rigging exists, although there is no clear statement as in the IOR and IMS that the boat must have a specified shroud or stay. Rotating masts are specifically prohibited. The same is true for the IACC Rule, called the AC90 rule (and specifially, rule #22). The wording implies a stayed rig, and the dimension restrictions on the mast preclude a mast that could be large enough for a free-standing arrangement. Rotating masts are specifically prohibited.

    The International 12 Meters are still raced. I would bet that the 6 Meter and 8 Meter classes, which are still raced, are similar, although I have not specifically read their rules. Racing rules tend to follow each other.

    As I said, I am not sure about the IRC rules and how free-standing and rotating rigs are handled.

    As for Eric Hall's J90, I sailed on that boat one time with Eric Hall when equipped with his #2 version of the rig (he is now up to #3). His experience as he related to me was that the free-standing-equipped J90 was every bit as fast (but not faster) than the rigged sister when sailing to windward. They were comparable. But when sailing to leeward, and particularly deep downwind, the free-standing rigged J90 was about twice as fast as the stayed sister--it simply ran away and ahead.

  5. Paul B

    Paul B Previous Member

    Actually, I was responding to your earlier comment:

    You told the other poster they would have to change the rules. So of course they would not try to change rules that are obsolete and/or no longer in use.

    This rule has nothing to do with freestanding rigs. It was implemented because some people started building boats that relied on the wire luff of the jib to support the rig. This was seen as a potential safety issue and was addressed.

    I know at least one Freedon 40 was rated under the IOR rule. Maybe they added a non-functional headstay to satisfy the rule, or maybe they were granted a waiver due to the type of rig they used.

    If you fit a forestay to a freestanding rig simply to placate the rule, and do not use it to apply any force to the rig, then you would not need any other rigging to "stabilize the rig".

    I questioned you comment about requirements for rigging. I know there have been regulations regarding mast rotation.

    That rig only had a forestay to hang the headsail on, and a running back to counteract the headstay sag. Under IMS you could have designed the same boat as a catboat with a freestanding mast.

    No one has built a modern 12 for more than 20 years, and no one will ever build another, yet you continue to obfuscate by mentioning that rule.

    Which of the currently used rules that would need to be "changed"? Let's look at current rules and see what's what:

    ACC: Seems open to freestanding rigs.
    IRC: Open to freestanding rigs (and presumeably rotating rigs as well)
    Open 60s: Open to freestanding rigs (and rotating masts as well)
    PHRF: Open to freestanding rigs (and rotating masts as well)

    So what current rules were you referring to that would have to be changed to allow freestanding rigs?

    In upwind racing the ability to hold your lane is essential. If you can't hold your lane you will be forced to sail on the unfavored tack until you are clear. You lose.

    The Hall's J90 could not hold a lane. It sailed too low up the hill.

    Your comment that it was "twice as fast" downhill as a stayed J90 is as funny as the comments about your Open 60 being "too fast".

    Attached Files:

  6. Eric Sponberg
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    Eric Sponberg Senior Member

    "Twice as fast" downhill--My quote is directly from Eric Hall.

    My open 60 being "too fast"--My quote is directly from Lars Bergstrom.

    They may be funny, but they are true.

  7. outside the box

    outside the box Previous Member

    Hi Eric
    Thanks for all the great information, much appreciated as always
  8. Bruce Woods
    Joined: Sep 2007
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    Bruce Woods Senior Member

    Sorry eric , twice as fast? thats like repeating "the earth is flat"
  9. Maciek188
    Joined: Jul 2005
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    Maciek188 Junior Member

    Hi everyone !
    Thank you for tons of priceless information on construction of CF mast, but let's stick to the subject and leave discussion of racing rules and regulations for another thread.


    "In the work that I have done on stayed and free-standing rigs alike, putting a core into a mast laminate is not worthwhile. In stayed rigs with all the load in compression, the load is carried by the skins and not the core. The core certainly adds thickness which makes the overall shape more resistant to buckling, but then you run the risk of inner or outer skin buckling which is just as bad. In a free-standing rig case, one side of the mast is in tension, the other in compression, and you end up with the same problem--better overall buckling stiffness with a cored section where the core carries no load, but increased skin buckling susceptibility.

    If engineered properly, the size of the mast section will have a solid wall thickness of carbon that is of sufficient thickness to resist overall section buckling. Much of this characteristic is dependent on the layup sequence, ply by ply, of the axial layers and off-axis layers. This type of construction is the lightest, cheapest, and easiest to build. To add a core to such designs only adds weight, cost, building complication, and the potential for core/skin voids and delaminations.

    I do not wish to criticize Rallard's effort for he may end up with a very nice mast. But usually, it is best to consult a designer who has been around the block on such rigs in order to get the best use out of the materials for the lowest cost and easiest construction.


    Would you say that it applies also to CF crossbars in light, 25', racing catamaran? Single wall tubes will definitely simplify construction and save some weight. Could you please comment on the subject, Thanks, Mike
  10. Eric Sponberg
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    Eric Sponberg Senior Member

    On a small catamaran such as you suggest, yes, I would say that going with a solid carbon laminate for the crossbars would be the way to go. Cross bars experience beam bending and torsion, where, again, the core would not contribute much to the structure over and above what the carbon fiber has to do.

    On larger catamarans where the crossbeams are also subjected to wave impact loads and their unsupported panels are quite large, then core construction would make sense.

  11. catsketcher
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    catsketcher Senior Member

    Fiber tension

    I have been away while and see that a little while back some people talked about aligning epoxy molecules. It is a bit of a side track but as a writer for an Australian magazine I got to see Ellen Macarthurs B and Q during the build and talk to her builder at Boatspeed. He uses male moulds even though the boat will need some filler because of a concept called fiber tension. Basically he likes the idea of pulling the fibers over the male mould with some force to straighten the fibers to absolutely straight. This will allow them to carry more load. He used the same method for Thomas Coville's Sodebo.

    I feel that ensuring correct fiber orientation is far more beneficial than orientating epoxy molecules which are not very linear anyway. The nice drawings of carbon chains are much straighter than what you make with a model kit (chemistry teacher talk)

    As an aside and a question for Eric - Is is possible for a designer like yourself to develop a laminate schedule for an equivalent alunimium mast at a cost that makes it reasonable for a one off project? Is it worth my while financially for a normal boat with an elliptical section mast? (In my case the boat is a 7 metre trailer sailer cat) Can someone develop more of a cookbook style of engineering for the home builder?


    Phil Thompson
  12. Alan M.
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    Alan M. Senior Member

    Is that the mast alone, or the entire rig?
  13. Eric Sponberg
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    Eric Sponberg Senior Member

    Is it possible? Yes. Is it worth it, especially for a 7M cat? Probably not. For small boats, you are not going to save very much weight which would be the main reason for building a carbon fiber mast. If done well, it would save 40-50% of the weight of the aluminum mast, but in total pounds (or kilos), that's tiny.

    I can give you a few guidelines if you want do some calculations on your own. An equivalent carbon fiber mast will have the same section and wall thickness as the aluminum mast. The density of aluminum is 0.096 lbs/, and the density of carbon fiber laminate is about 0.057 lbs/ If laminated well, the strength will be about twice as high, but the stiffness (modulus of elasticity) will be about the same. If done poorly, strength may be equal to aluminum, and stiffness may be half of aluminum. Most rigs are stiffness critical, so modulus of elasticity is the driving factor. For given wall thickness, 80% should be unidirectional, and the remainder off-axis, split evenly between +/-45 deg and 90 deg. The layup should be a mirror image of itself through the centerplane of the laminate. That is, the layup should go +/-45; 90; 0; 90; +/-45 in the proportions described.

    I have often considered developing "stock plans" for masts, but each time I go through the exercise, I always arrive at the conclusion that each boat and each mast and each owner and each builder are different. Everyone one of those factors will make the laminate schedule different. So there is little point in making a stock plans--the market is too small and the liability too great. So I stick to custom designs.

    For small boats, say up to 30' or so or a bit larger, aluminum masts are fine. You get good quality, good engineering characteristics, and low cost.

  14. rob denney
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    rob denney Senior Member


  15. Boston

    Boston Previous Member

    ya I thought it would maybe make the epoxy bond more efficiently to electrically align the molecular components
    even found a paper supporting the idea
    but it didnt seem to generate much interest
    oh well seemed like a good idea at the time
    if you have any experience with it I'd love to hear about it
