Mast building.

Discussion in 'Multihulls' started by redreuben, Aug 18, 2012.

  1. Silver Raven
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    Silver Raven Senior Member

    Gooday Eric. Thanks for all that. I think I should just go-away here & bail out before someone takes what I have to say the wrong way & gets up-set or angry neither of which is my desire.

    'A' class (oh & the others - 'B' & 'C' class as well) have many design parameters going on all at once. I've designed & built 2 world champoinship 'A' class cats - built a wing-masted 'B' class cat that was a tad quick, built a 'C' class & wing-masts & played with the Cunninghams for a few years - & now we have the AC 45's & the winged AC 72's - all of which have something different going on for them than the good Dr. had to say back then. I wouldn't have believed him then nor do I now. I would put to the good DR. & yourself that it is shape & foil section that is what should be being looked into here not 'the thickness or even the area of the mast'.

    12 years befor the good Dr. made his comments we had designed - built & were leading the world in 'B' class speed & wing masts development with a wing that was 14" thisk @ 18" back from the leading edge - was 60" from front to back at the base - was 48" front to back @ 25' up the mast - was 28" at the top - whcih was 38' high (or long) - was considered to be 128 sq ft as 1/2 the total surface area of the wing-mast - for rating purposes - weighted in @ 100 lbs - c/w all the rigging but without the soft sail fitted into the mast groove. As these are recorded facts - in hard copy - in severla books - I have some trouble understand what the Dr. was refering to & just how many boats he designed, built & sailed to prove his comments. As I've said - I think I'm outta-here. Facts are only good if they can be proved - if they can't then there not worth all that much, at least as I understand the world of sailing.

    So rather that upset anyone - I feel I should just bail-out at this point & crawl back into my box. I'll continue to discuss these matters with Gary Baigent as I am sure I wont upset him.

    Thanks again for your assistance, I really do appreciate your time. Ciao, james
     
  2. Eric Sponberg
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    Eric Sponberg Senior Member

    Whoa, wait a bit, Silver. I did not mean to be critical, quite the contrary. I admit to knowing nothing of racing A, B and C class cats, so I am ignorant of anything that you have learned or know. I was merely trying to point out an engineering aerodynamic concern of wingmast sections. You asked me a question as to why are big masts not desirable, and I tried to answer.

    First, Dr. Jerry Milgram is a highly regarded researcher at MIT, has been for decades, and he has designed some boats. The paper he wrote was the result of some sail foil sections he had tested in a water tunnel test program. Some of his findings have been the foundation of mast design in the US ever since then.

    So you apparently have experience that is contrary to that, which is really interesting, and I am sure we all would like to know more. Can you elaborate on your reasoning: How has your thinking and practice evolved over the years to bring you to today? Can you supply some examples from your racing experiences where bigger sections masts sail faster/better/higher than smaller masts? What have you noticed in mast design and construction that is favorable? What could the rest of us possibly be missing?

    I'm all ears, really, and I think you can educate us. So please, don't go away.

    Eric
     
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  3. cavalier mk2
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    cavalier mk2 Senior Member

    Hi ho Silver and away !.....perhaps the difference is between masts/rotating masts and true wing masts/ wingsails which are 2 different things. Did you guys figure out how to reef one for cruising? Birds of a feather and all that..... the feathering in a storm thing hasn't worked that well but then nature would have its creatures folding their wings.
     
  4. Petros
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    Petros Senior Member

    Eric,

    I find this all vary interesting, I am a bit curious about the lay-up schedule you show on the mast build-up drawings you posted. You show two layers of bi- one at 45 deg and one at 90, than a layer of uni along the axis of the mast, than two more layers of bi as before, and than another layer of uni with two layers of bi on top. Why do you need the two layers in between the two layers of uni-directional? would it not be more efficient structurally to omit these in between layers of bi-directional cloth? Does it help stabilize the build-up?

    I do not know a lot about composite construction, I want to understand the logic in this.
     
  5. Eric Sponberg
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    Eric Sponberg Senior Member

    Petros,
    The drawing is a bit of a schematic in that it does not indicate how many strips of carbon fiber unidirectional tape are applied to the mast. That is detailed in the laminate schedule, which is another part of the drawing. The laminate for a wingmast is made up of about 80% unis and 20% off-axis fabrics. Of this 20%, roughly half must be +/-45 DB, and the other half 0/90 Biax. This mix determines the mechanical properties of the laminate. The off-axis fibers all go to stabilizing the section shape so that it won't collapse. They also handle the shear loads in part, and they keep the mast from twisting, at least from twisting too much. The very first pair of DB and Biax have to go on the very inside of the laminate, and the very last pair has to go on the outside. Together, these layers form a sandwich that keeps the unis in line. If they were not there, the unis could actually buckle and break out of the laminate. Those 4 layers, at least on this mast design, were only part of the required total. The lower half of the laminate was quite thick, and so more layers are required. On this mast, they were placed in the center of the laminate. The stub mast for this design, which sticks up through the deck and on which the wingmast sits, was so thick that it had 9 pairs of DB and Biax layers in the laminate. These were spaced evenly throughout the laminate, again with pairs on the very inside and outside, the DB always on the surface.

    I hope that explains things more clearly.

    Eric
     
  6. groper
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    groper Senior Member

    Sounds to me like silver raven is talking more about a total wing section, rather than just a wing mast as we typically see them today. I realize he also mentions a soft sail track behind it, but the dimensions suggest more wing and less sail than we normally see.

    Clearly, we see the AC45 wing sections are rather thick at their maximum - which i think is what silver is relating to - does anyone know the section thickness? i would assume its about 33% aft of the leading edge, and from the photos looks to be in excess of 12-15inches.

    I dont beleive its fair or correct to make a comparison between a small wing mast, and a full wing section thicknesses as the 2 are not measured from a mutual chord point. however, if the wing mast extends to ~33% chord, and is therefore a rather large planform, and a significant part of the airfoil whole, then i guess things would almost be fair.

    Nor would it help, to compare thicknesses of a round or oval shape mast, to a full foil shaped mast with respect to drag.

    Eric, it would help, if you explained the MIT research a bit more clearly or in more detail. Like;
    Were the masts studied only round, or were various other section shapes, foils etc looked at?
    If foil shaped masts were studied, what was the range of chord, thickness and length vs total sail area studied?

    When looking at drag, proven theory tells us its directly proportional to sectional area.
    Trouble is, when looking at soft sails, how much luff do you have and how much sectional area is the soft sail presenting?
     
  7. Petros
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    Petros Senior Member

    Not quite. I understand the reason for the orientation of the layers, I am a structural engineer and understand what happens internally when the materials are stressed. It is the order in which the layers were installed that I am curious about.

    If the primary loading is in bending and compression, than it seems to me having as much of the uni-directional layers toward the outer skin as possible would be more efficient in terms of strength for the given amount of material. It just seems the middle layer does not contribute as much to the strength. Is the middle layer there for a specific reason, or is it traditional to alternate layers like that to stabilize the layers?
     
  8. Petros
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    Petros Senior Member

    I think I can answer the aerodynamic question, I worked for 3 years in aerodynamics early in my career.

    The best lift to drag ratio of any lifting surface will come with the thinnest cross sectional foils. the thinner airfoils will have lower drag for any given lift. The problem is of course is really thin wings, or masts, would be very heavy. so there is a compromise between wing thickness and structural weight. So even if you have a rigid wing sail, the thinner the section, the less drag it will have.

    The mast on a conventional sail disturbs the flow over the leading edge of the sail surface, the smaller the mast, the less disturbed air, the more lift off the sail and the less drag of the rig. Stream lining the shape of the mast, and allowing it to rotate, will disturb less air, but there will always be an area of separated flow right behind the mast on the main sail. The shaped stream lined mast section will also contribute to the thrust (or lift off the sails), but it will still generate more drag than a smaller section. But of course a smaller section mast will be much heavier. More spreaders and shrouds will allow for a smaller mast section, but the spreaders and shrouds also generate a lot of drag as well. So there are trade off to be made.

    I have always wondered if there would be an advantage to making a sail without any spreaders or shrouds, optimizing the L/D rather than just the lift, if the extra weight and mast size would be a worth while trade off. But as Eric points out, that would be a very costly experiment to find out.
     
  9. Silver Raven
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    Silver Raven Senior Member

    'Foldable - Reefable' wing-masts

    Gooday 'Cav' Suggest you look at the parallel discussion (& please you also Eric) called "an interesting boat: Matinbleu (free standing "wingsails")

    Great concept & it works. Big boat - big money & way over my head & outside my current pocket book. \\Even more interesting is Gary Baignet's project - smaller much more affordable - inside my pocket (got big water-proof pockets -I do) - it works & everyone that wanted to do it could afford it & the rest of us could/will learn lots from Gary's whole approach to this subject. Well done Gazza. 10-mate ! ! !

    If the good Doctors theory is correct - then there - technically speaking - can be no difference "between masts/rotatiing masts and true wing masts/wingsails which are 2 different things.

    I'm not buying any part of that. A mast is a mast is a mast - - regardless of any other attachments to it - it is still a mast - full stop. It's the Dr's statement about masts - that I'm not in agreement with - for as I see it - the statement just does not hold-up to cross-examination.

    'Experiments' in 'test-tank' situations are not automatically directly transferable to - on the water sailing happenings. His - 'drag' calculations need to include the paramaters of 3 oscillations all happening simultaneously. - ie - forward, sideways, up & down - which is how boats sail either through &/or over the water. All masts are then subject to - several times that amount of movement in those 3 eliptical force fields - thus a thinner 'flat-plate' is not faster - over-the-water to a fatter foil section - in real-life sailing situations.

    As the 'break-away' of laminar-flow happens from front to back with/to a hard surface mast & from back to front for soft surface fabric sail - coupled to an air-foil being far superior to a flat plate then I am sure the assumptions previously made - need some further analysis. I M H O .

    Help - Tom Speers - 'Blunted' - Gary Baigent - Steve Clarke & others - some of which are most probably not in a position - at this point in time - to enter into this conversation - due to prior commitments..

    First or second; - - HELP - Gary - I need some assistance to explain what I'm trying to say -

    I will not enter into a - ****-fight with anyone about sailing - not ever. I really appreciate Eric's comments & outlook into these matters & am very grateful that the discussion is not ever going to get personal - Thanks for that - Eric. I didn't take what Eric said anyway but in a positive manner, again - Thanks Eric.

    Now - Cav - There is/are - 'reefable' or 'foldable' wing-mast like sections that work & have worked for many years.

    Again - HELP Gary - the little red 'rocket-ship' is how old ??? & still works at what (in a 1 out-of 10 ratio) - [suspect about 6 to 8 out of 10 at least] performance ability - in real terms - sailing in the real water & in true winds.

    Gawd - like Eric - I do so wish I had endless amounts of money to get everyone together in a very large shed & build some of these 'concepts' full sizeeeee & then we could all take them out for a sail againt a common data-base vessel. However - reality calls the tune here - my issues have to be settled first, the bills have to be paid second & some important sailing desires must be bought & paid for - just before I spend hard-earned monies - on my dream of a more efficient sailing craft.

    I do wish we might cross link these two 'forum' discussions - for I think they are joined at the hip.

    Ciao all, james
     
  10. Petros
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    Petros Senior Member

    silver,

    You are conflating a number of different issues with regard to the aerodynamics of the sail. Anything that deflects airflow is a "foil", no one said anything about flat plat, a thin sail in a curve will deflect airflow, and is therefor a foil. Heck even a flat plate at an angle to the flow will defect it, generate lift and could also be considered a foil. But you know you see hang gliders and many ultralite aircraft that have single surface wings, only as thick as the fabric, and they still generated lift (and act as a foil).

    And I did not mention laminar flow, but attached flow vs. detached flow, the flow could be laminar or turbulent, and on a sail and mast it is almost certainly turbulent, but it could still be attached and generating lift. If it is detached from the surface is does not generate much lift, but it will generate a lot of drag. You can not acheive laminar flow on a conventional sail, the object is to keep the flow attached to the surface. The mast prevents large areas of the mail sail from having attached flow, which means those areas only create drag. the small the mast dia, the smaller the area of detached flow, and the more of the sail will generate lift, and less drag. so the lift to drag ratio is greatly improved.

    No matter if the boat is pitching and rolling, the smaller the mast, the more area of the sail will generated lift. There is no way a larger mast will generated the same amount of lift even if pitching and rolling in the wind, I do not understand why you think this can not be so. The only time you get lift (or thrust) off the sails is when you are "bending" (accelerating) the moving air over a curved surface.

    F=ma, the force (or lift) off the sail comes from the mass of the air moving over the surface being accelerated in a curve. When the flow in disrupted by the mast, shrouds, spreaders, or large areas of separated flow, it slows it down and there is no acceleration, no lift.

    Any object that generated a thrust in a fluid, which includes air, MUST operated in this manner. Be it a wing on an airplane, a sail, a propeller (a foil going around in circles), it must accelerate the mass of the fluid to created the force of thrust. F=ma.

    large round masts disturb that acceleration.
     
  11. Silver Raven
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    Silver Raven Senior Member

    Petros. I just don't know where to start with what you are saying.I'll tri the first sentence "You are conflating a number of different issues with regard to the aerodynamics of the sail".

    Sorry bloke - at that point you either did not read carefully what I typed, or I am not able to express my self in you language or we are not reading the same sentence in the same paragraph, page, chapter. etc. Never mind - you must be seeing some overly pedantic difference between what I quoted Eric as quoting Dr Jery Milgram as having said.

    Your definition of most of your examples - is totally beyond my abitlity to make any effort of challenge your obvious errors. We'll skip the middle bits - cause you're definately not sailing the wing-masted boats that I've been sailing - & we might go to your last sentence -

    "large round masts disturb that acceleration" - I fail to see where anyone has mentioned that example before - or is that "conflating" ??? - as I don't use that term in my everyday language - & am obviously not as familiar with 'it' as you are - like the rest of your hypothesis - I'll leave you to it while I go sailing & build another wing mast 14" to 18" thick that - doesn't work & doesn't do it faster than a very thin fiol mast section. Good luck with your sailing success.

    Suggest you tell all the blokes designing, constructing & sailing the wing-masts being used on 'A' class - 'C' class - SR33's - AC 45's & AC 72's - that they are wrong - cause their masts are not - as thin as they could/should be. I'm sure they will all stop work & await your superior wisdom. Ciao, james
     
  12. Gary Baigent
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    Gary Baigent Senior Member

    Silver James, like to keep clear of this - because will end in rage and tears. But the longer the chord is on, say, a 30% thickness ratio wing mast, the lesser the amount of turbulence on the WINDWARD side. The lee side is always smooth, fast and clean, no problems. To achieve this, the soft sail luff needs to feed into a foil, not be gapped with carriages and bolt rope. A gap there, imo, destroys wingmast performance, almost as bad as conventional fixxy. I know, I know, easier to lift, drop etc. Live with the better airfoil solution.
    Also there is no comparison between wing mast and fixed round or oval in drag and turbulence; just watch all the woolies stream or flutter. Fixed rigs, no matter how small a section, destroy flow in the area behind the pole.
    Combined with a good airfoil wing/soft sail, you need foils on the platform (sorry for the bias) to dampen out killer pitching to maintain rig airflow attachment.
    Spreaders are unnecessary if you've designed and constructed the wing mast properly.
    Here's an ancient shot of Supplejack's rig (near 35% thick/chord)- you can just feel the old rig breathing correctly, boat sailing fast and effortlessly. Did I say I was biased?
     

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  13. FMS
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    FMS Senior Member

    "conflating" means to combine or fuse two or more ideas or things into one.
     
  14. groper
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    groper Senior Member

    i dont think we are all on the same page here...

    rotating masts or fixed, if rotating, what section chord thickness ratio?

    too many variables...

    strength vs thickness is a very real governing factor, and i suggest is the most limiting in terms of overall design...

    another consideration is the ability or ease in which the sail can be trimmed... just because an arbitrary foil/mast/sail might have a thinner section, doesnt mean the boat will be faster as a thicker section is less sensitive to ideal trim. So depending on the skill of the sailor or the variability of the winds across the sea, the thicker section might be faster because, on mean average, its trimmed better???
     

  15. Silver Raven
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    Silver Raven Senior Member

    Gooday bloke. Your last sentence is correct & not truely a question - as you've shown (???). The racing records in Sydney, Botany Bay & several other places show that "the thicker section might be baster, because on mean average, it's trimmed better" & more of the time. As the wind moves constantly in 2 axis both at once - then keeping the - mast/sail/wing - whatever is powering the vessel is rather difficult. The wind in increasing & decreasing in a 15 degree arc & at the same time it is increasing & decreasing in wind speed - also at the same time - so keeping @ 90 to 100% is just not possible nor is it humanly able to be done. The 'thinner' wing-masts that were competing at that time were less that 1/2 as efficient - again the race records will show this.

    Groper - thanks for your putting it much clearer than I have been able to do.

    FMS - thank you - I also have a Dictionary (1999 with over 2000 pages) & a Thesaurus (also 1999 with over 350000 synonyums & antonyms) & they live right beside my computer - they help me a tad bit with my 90% dyslexia - which is at time a bother - no end.

    Gary - I read - I heard & I understand - & I thank you .

    Ciao all, james. - Does anyone know how to eradicate pest weeds in my garden ??? jj
     
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