Carbon Mast FEA

Discussion in 'Boat Design' started by nemo, May 12, 2004.

  1. nemo
    Joined: Apr 2002
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    nemo Naval Architect

    I've tried to build a finite element model of a mast that has to be changed.
    The actual mast is an Alluminium one, 7/8 with running backstays, its lenght is 13,5 m and it's very elastic. The new carbon mast should have almost the same bended shape, because the mainsail should be the same.
    The Finite element results say that the carbon mast will be the 37% stiffer than the alluminium one. It means roughly that if I want the same bend, the backstay and running backstay have to be the 37% more powerful.
    Anyone out there with similar experience? Does this result make sense?
    The carbon mast was modeled with 6 unidirectional plies, two 45° biaxial plies, and a weave ply.
    Here are a couple of pics of the deformed shape and the displacements.
     

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  2. Thunderhead19
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    Thunderhead19 Senior Member

    I ...oh..never mind
     
  3. SailDesign
    Joined: Jan 2003
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    SailDesign Old Phart! Stay upwind..

    Is that you, Emily? :)
     
  4. PaulCoffin
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    PaulCoffin Junior Member

    You should be able to confirm that this is a reasonable solution for you geometry and laminate with simple mast x-section moment of inertia calcs using the correct axial modulii for the aluminum and carbon fiber laminate.
     
  5. tspeer
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    tspeer Senior Member

    I thought stiffness was the whole point of going to carbon!

    You could reduce the cross section to make the stiffness equal to the aluminum mast. That would improve the aerodynamics of the rig.
     
  6. matthewuk
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    matthewuk New Member

    37 % stiffer does not tie in with "The new carbon mast should have almost the same bended shape, because the mainsail should be the same"
    Assuming your current rig works well, why not layup the mast so it bends more similarly to the alloy one?
    If you are going to increase your rig tensions by substantial margins, will the hull take the loadings?
    and dont forget GIGO with fea. garbage in garbage out. The best idea i ever heard with fea is to never believe the results, always try to prove the results erroneous right up untill you are forced to admit that they might just be right, and then CHECK AGAIN. lol Which fea package are u using as a matter of interest?
     
  7. nemo
    Joined: Apr 2002
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    nemo Naval Architect

    37% stiffer means roughly that I need 37% more force on the backstay than the actual force on the alluminium one. Yes the boat would take the load..
    I'm afraid that reducing the diameter would lead more easily to buckling failure.
    Fiber orientation could solve the problem, of course the mast would be very stiff with all the plies being unidirectional, I tried to put in more 45° plies, and it works. I also changed the laminate layup on some stress point, such as stays and spreader attachments.
    I know about the "GIGO", that's why I asked a confirm here..the goal of fea software should be verifying something without building anything, but it's difficult to completely trust it! :)
    My Fea package is Strand7, I think it's very good, and has a complete composite material support, quite easy to use..
     
  8. Thunderhead19
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    Thunderhead19 Senior Member

    No, I'm not emily.

    I made a post about reducing the diameter of the mast and how if your sail area was the same that your loadings wouldn't change on the stays unless you were deliberately bending the mast. And I added that isotropc and anisotropic materials have fundamentally different behaviour and that you shouldn't expect to be able to duplicate the performance. I also pointed out that your load shifts from the stays to the base of the mast with a change in rigidity. Since I know basically nothing about mast and sail plan design, I tried to delete my post before I looked ignorant. It was impossible
     
  9. wind
    Joined: Apr 2005
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    wind Junior Member

    Help

    Nemo , I am in the 3 year of Naval engineering, and I am learning FEA, Can you Help me with the FEA in a Carbon mast, please, i need a Table with the material layers and all the modules, thank you, and sorry for the time I made to you lose, I hope you can help me.
     

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  10. cleblanc
    Joined: Dec 2004
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    cleblanc Junior Member


    If you look at the site, it seems to be for a Mini transat. The skipper WILL deliberatly bend the mast!

    I know that in beach catamarans, there are two option for the carbon mast: reducing the overall diameter or reducing the wall thickness

    The thinner wall thickness will give a much lighter mast for the same stiffness and it seems that this will give a good performance gain because it reduced the inertia of the rig.

    the other option was to use a reduce diameter. Actually, it is reducing the minor axis and major axis of the cross section because we are talking about profiled mast sections. The result is a more areodynamic rig but on a rotating mast system, the performance gains are not noticeable since the mast itself becomes an efficient part of the sail profile.

    The last comment is about the stiffness and the modulus of carbon:

    Carbon has two main improvement compared to aluminium: Better strength to weight ratio so a lighter mast is possible

    Much better modulus (Carbon = 400-500GPa, aluminium = 70GPA) this means that with the same stiffness, the carbon mast will transfer the energy of the sail quicker to the stays. This "reflex" effect also required very stiff stays like solid rods instead of wire.

    The last thing is that you can have a taper mast in carbon and this will help even more with the weight.

    Mast really is the best mast building material. The only problem is the galvanic corrosion with the graphite.

    Keep us posted on your designs, I will be looking for a mast next year for my 30' weekender catamaran and I would really like to go with carbon

    Charles Leblanc
    Sept-Iles, Quebec, Canada
     
  11. stewi
    Joined: Sep 2005
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    stewi Junior Member

    Excuse my questions as a non-naval engineer. Wouldn't you reduce the number of unidirectional layers towards the mast top? If you use 6 layers, wouldn't you rather have 3 layers going all the way and 6 layers at 50 % length?
    Isn't the 7/8 designed rig meant to have more mast bent in the top and the sail shape designed for this particular rig?
    If the carbon mast bends evenly over the entire length, wouldn't you have to buy another main?
     
  12. trouty

    trouty Guest

    I don't like your choice of material...

    Remember carbon fibre has a S to F ratio (Strain to Failure ratio) of less than 1% in many (most) applications......

    Now - if you do the Euler wall buckling theorem eqautions on this carbon fibre layup, - you'll likely see - that, in all likelihood - this design - will first deform to an oval - and then collapse on the wall under compression, before exploding into a thousand carbon graphite powder pieces, with a sound like a canon shot!

    Try to think of it this way...

    A half inch diameter tube of carbon Graphite, while albeit a very "stiff material" (ability to return to battery)...can only be bent into a 50 inch diameter (4 ft circle) before the compression side and tension sides are at S to F ratio of 1% and ready to deform to an oval and then collapse under Euelers wall buckling theorem.

    Would anyone want that in a yacht mast designed to be under varying loads, bending and straightening etc etc - many times over all along ot's tapered length?

    E2 galss and most of the fibreglass composites, are MUCH more forgiving (albeit heavier) in this application...with their S to F ratio's of approaching 4%

    Back to the half inch diameter tube...

    Bend it to a 12 inch diameter circle (one quarter the size of the carbon / graphite tube cirlce) and now it's approaching it's 4% S to F ratio....

    In a bending situation...it's 4 times as forgiving as carbon fibre graphite materials.

    The reason I point this out - is that - mast design - and fly rod design are basically parallel design sciences.

    We had a trend in fly rods design / building a few years back toward ever lighter / stiffer, fly rods - that would throw a fly line further, due to the higher modulus of the carbon over more traditional glass.

    This they did do well - throw fly lines - man could they throw flylines and light - you could use em all day!

    One one drawback - they couldn't fight fish for shyte!

    Two different requirements - to stay stiff and throw a line - and to bend like a bass-turd to fight the fish once you've hooked it.

    After a boot full of broken $1000 graphite fly rods - I finally figured out - glass was a much better fish fighting tool...over the graphite casting tool.
    (The manufacturers are still playing catch up ball however - I was in fact a destruction tester for the Powell fly rod company for a while...I was too good at my job, - there weren't any I didn't bust on fish!).

    Me n Eueler - we are on first names basis - I've tested his theorem like no one else on earth!

    Not much point casting anything at a fish if it can't land it once you've hooked it.

    Translate that experience to carbon graphite masts & you might save yaself a few zillion $ in R & D.

    Cheers!
     
  13. Chris Ostlind

    Chris Ostlind Previous Member

    Bending Graphite

    Hey Trouty!

    Cool letter and chock full of nice data on fishing poles. The real question, though, is aside from some preliminary understanding of bending moments and wall/diameter thickness ratios, what really do fly rods have to do with sailboat masts?

    The deflection amounts being discussed in sailboat masts is about as much as is encountered when a fly rod is taken off the rack and moved about trying to get a reel mounted.

    When was the last time you saw a mast bending over to 180 degrees of fixtured position? Failure under those loads... why, yessir, you got your wish.

    The whole point of carbon masts is reducing weight aloft. If you have to substitute glass/epoxy for the job, then aluminum spars are a much better deal from a price/benefit position.

    Best,

    Chris
     
  14. trouty

    trouty Guest

    Hmmm

    Hi Chris!
    Do we go there?
    In for a pound, in for penny I guess!

    Alloys better than glass - granted...

    What are the similaritys? twixt fishin poles n masts?.

    Well - if you can't see em - maybe I'm wasting my time, but what the heck.

    Do yachst capsize / get knocked over occasionally? What stresses do the mast take then (or doesn't it matter of the vessel rights itself sans mast)?

    When all goes well and the masts supported nice by it's stays - I guess - the loading is probably a little different (but remember, fishing poles have line runners bound on that span across the flexing pole, affecting the curvature of the pole, in a similar way to the stays fixings affecting the rate at which the mast bends) etc.

    Now - you might be right about alloy and Glass - but there are also other options...(remembering I was chiefly talking about S to F ratio's).

    Some of the leading fly rod designers are experimenting now - with rods made in 3 sections of 3 different materials.

    What I was alluding to, was that just like a mast - a fishing pole as you deridingly call a fly rod, has to perform different functions over it's length and each different section has to do different things.

    The tip section needs to be deft enough to feel the slightest touch on the end of the line while fishing - it also has to form the tight loop with a small frontal resistance to the wind, in the fly line and so on.

    The midsection - has to absorb shocks from fish headshakes, and sudden lunges and runs and the butt has to lift damn things like tuna's up when they are circling right below the boat and seem to be stuck there with glue.

    Masts likewise are to perform different functions as they ascend...supporting the boom part way up - fixing to the deck at the butt and so on.

    They are all tapered poles designed to flex - if you can't see that - then likely I can't help much.

    Back to 3 piece non similar material rods...

    One designer I know is messing with glass butts - high modulous carbon graphite midsections and Boron / Titanium tip sections.

    Why can't a mast be built this way?

    Why does it have to be a one material versus another discussion?

    Go back to parent materials basic properties - (including S to F Ratio's) and take a real good look as a designer - of what each sections required perameters are - select the most appropriate material - and look for ways of getting the taper / composites layup & material properties to = each other where they meet...

    Ya see - thats lateral thinking.

    It's like when the light globe goes on and someone thinks - "heck - thats a good idea - why didn't I think of that?"

    Coz they can't think outside the square - thats why, and often times - their training being so constrained - they aren't thought to think outside the square.

    Being upside down all the time -with the blood rushing to our heads - we are always looking at the world differently to most...Ben Lexcen should have taught you guys this already...seemingly you still haven't cottoned on yet!;)
    (Ben is the one invented the winged keel what whupped yo Azz downunder in the America's (cough) cup)! ;) :p

    Like I said - probably waisting my time - but at least I try!:D

    Cheers!
     

  15. Chris Ostlind

    Chris Ostlind Previous Member

    Pole, rod, it's all the same

    If Ol' Ben was so smart... were'd the Cup go?

    Since it weren't Ol' Ben's keel that done-in the boys from Perth, it musta been the pseudo, ultra-bendy, fishin' pole that the Old Boys used for the mast that lost the Cup. Seein' as how they work just the same.

    You can't seriously be comparing the use of a pole to a mast, can you?

    Let's see: a mast is fixed to a platform from which it bends, The relationship of the mast to the platform remains constant... a pole is allowed to move all around the environment in the hands of the fishing dude. Not so good a comparison, really.

    A mast typically has spreaders, shrouds and various assortments of stays in order to remain in column... a pole doesn't. Well, not any pole I've ever seen. Another not so good comparison.

    A pole is meant to have constant and severe dynamic stress applied (and this is where that silly notion of holding the rod straight-up while the mighty tuna is just below your feet comes in) A mast's dynamic flex range is considerably different and never meant to be capable of bending to a 180 position. I'd really like to see the mast you use that can successfully do that, in fact. Please attach photos. A really not so good comparison.

    A mast has to live in an aerodynamic enviornment and it has to contribute to the overall efficiency of the attached sail. No such application exists for the fishin' pole. Well, unless the owner of said pole likes to disturb the breeze around his fishy smell.

    Masts and poles can be built from "similar" materials, but not necessarily the same ones. My bet is that the epoxy formulations, the carbon materials themselves and the properties of the two products are completely different. This comparison of yours is like pointing to a Ferrari and a Yugo and saying they're in the same game.

    Yes, masts and poles are sort of cylindrical in form and yes, they both have sports related context within which they operate. That's pretty much where it ends, I'm afraid. They're different products with different applications that just happen to appear like they live in the same realm. Exceptin' you got the Yugo and we got the Ferrari.

    The notion of differing flex characteristics within a given mast structure is not a new notion at all. The windsurf industry has been building sticks like that for more than a decade now with just that process. You fishin' dudes need to get on the buggy before it leaves town. Study filament winding technology with more than a can of Foster's:confused: in one hand and a back-wound reel in the other. Amazing things can happen.

    I know it's potentially mean-spirited to insist that you get yourself out of the dark ages technologically, but someone's got to do it while you still have a shot at some glory.

    Really, Trouty, and I mean this sincerely, this has been fun and all in good jest. It's kind of you to jump-in with so much fervor. The discussion is much more lively with your contribution.

    Best Regards,

    Chris
     
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