Epoxy/glass mast for a cruising yacht?

Discussion in 'Boat Design' started by Robjl, Nov 2, 2005.

  1. rob denney
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    rob denney Senior Member

    G'day,

    Forgot to mention. Resin infusing a mast is asking for trouble.
    1) It will not be any lighter than a vaccuumed mast.
    2) The scope for dry laminate is huge
    3) It is near impossible to get the off axis laminate on tight before applying the vacuum. Consequently there are bound to be kinks in the off axis as it conforms to a smaller circumference.
    4) Carbon filaments are much smaller than glass and pack much tighter. Consequently, getting resin into and through the laminate is a struggle. Having said which, a company in NZ has apparently infused a couple of 18m unstayed masts. Not sure if they did them in one hit, but I suspect not.
    5) Infusion is wasteful of resin, with enormous potential for losing the whole job. Practise a lot, and start on small jobs, then move onto big ones.

    regards,

    Rob
     
  2. Inquisitor
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    Inquisitor BIG ENGINES: Silos today... Barn Door tomorrow!

    In researching aspects of sailboat design, I often run into all the technology, skills and relatively cheap labor you have in Australia and New Zealand building sailboats. Even from here, it feels like a hot bed of development. I am quite envious. Here, there are hot beds, but they are not near me and tend to be for the well healed. I am hoping to eventually get a 40’ Cat built, provisioned and in the water for under $200K. A more knowledgeable associate here thinks $100K is possible. In any event, my expectation is that I’ll be very intimate with fiberglass/epoxy (and many other techniques) before my time is done.

    Even from your bulk numbers, I’m looking at $15,000 in material costs for a carbon mast… Even though, I worked (analytically not fabrication) with carbon for most of my professional career and strongly believe in it, I could never justify the risk of ME taking that material and attempting a mast myself. I would definitely leave it to the skilled technical experts such as yourself. A wild *** guess (WAG) of even $30K for a carbon mast kept me from looking to see what the real number would be.

    An aside… anyone got a clue what 60’ Aluminum mast will cost me to get to Atlanta or a source for that? My WAG for that was about $10K.

    I had given it some thought for some time (obviously with AE glasses on) but when looking at a finished mast for less than a $1K it was worth my free (to myself) analytical ability. When someone knowledgeable in the boat design/construction (Robjl) piped up with the same hunch, I had to respond.

    The ONLY thing keeping a G/E mast from working is the great divergence in AE versus hand-lay-up properties. We’ve still to figure how low a workable analysis might be AND how high properties can be if all the stops are pulled-out. Just maybe, they’ll converge.
     
  3. stewi
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    stewi Junior Member

    Hi Rob (jl),
    I may misunderstand your approach. Please clarify
    You want to build over a male mold. This appears to be not a good solution compared to a female mold. While the material shrinks during curing it will wrap around the mold, whereby in a female mold it will get easier out of the mold.
    If I understand correctly, you want to complete each section with all layers and than put them together with the taper. I didn’t do the math, but I guess the compression loads on the mast are about 10 times the boat weight. What prevents the taper of splitting open the other sections?
    I can understand your reasoning for a hollow mast, but I would rather use either one long female half mold, or put only the first layer in one section, glass all section together and than do the unidirectional strands over the sections followed by the bi-directional fibers.
    I would also consider using some sort of ribs or spacers at the spreader locations. The spreader and shrouds will create quite some compression loads on your hollow mast.
    Attaching aluminum hardware to your finished (carbon) fiber mast gives me somewhat a shiver. Make sure, you don't cut any unidirectional strands. I would try to incorporate the T-slot into the design, or glass the slot on with woven fiber tape. You could use a foam profile, which is removed with thinner or a balsa wood strip, which is milled out with a t-slot bit and router.

    Without support the mast will bow while you glass it. You’ll require some support stands with Teflon rolls.
    Regards,
    Stefan
     
  4. stewi
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    stewi Junior Member

    Inquisitor,
    look in the yellow pages for local aluminum profile. Get a quote on a custom profile. The cost for the matrix, or however that part is called in which the alu is extruded, is not that expensive. It is a steel plate, which is wire EDM. My guess $ 2,000.
    Although I prefer a mono our masts may be the same and we can split the cost.
     
  5. rob denney
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    rob denney Senior Member

    Inquisitor,
    Definitely interesting places, but not so cheap. We are about average at $AUS65/hour for our shop. The carbon price I quoted was ex Texas. Most of our other materials are also imported.

    Not sure about your 40' cat prices, but we sell all the materials to build a 50' harryproa to sailing stage (rig, rigging, paint, timber, epoxy, glass etc) for $AUS50,000/$US35,000. You will indeed be very familiar with glass and epoxy by the end! My experience is that, until the exchange rate gets below 70c, the shipping costs make it about as cheap to buy materials in the USA as to buy them here and ship them over. This obviously does not apply to the tow.

    The unstayed 18m/60' mast we have just built weighed 120 kgs/262lbs for the bare tube. Say 40% of this was resin (48 kgs), 40% tow and 20% (24 kgs) off axis material. The materials cost for this was $Aus2,200/$US1,540. Be a lot less if you bought the tow in Texas rather than shipping it to Aus and back. Our suppliers would take a couple of boxes out of our shipment and send them to you. No need for you to buy the half ton. For us to build the tube is about a weeks work for two guys, say $AUS5,000/$3,500.

    I am not sure about the properties divergence. What resin fibre ratios are you getting in AE? We generally get about 60-65% carbon fibre by weight under vacuum. Autoclave pressures (7 atmospheres) and prepregs do not get much better than this. Infusion can never be better than a properly bled vacuum laminate.

    If you can do appreciably better than this in glass, then you should use that technique with carbon, you will get a markedly lighter and stiffer mast.

    Regards,

    Rob

     
  6. stewi
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    stewi Junior Member

    Thank you Rob,
    I was telling him already and I guess, he is referring to me "A more knowledgeable associate here thinks $100K is possible."
     
  7. Inquisitor
    Joined: Nov 2005
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    Inquisitor BIG ENGINES: Silos today... Barn Door tomorrow!

    Rob,
    Normal procedure was to use between 75-78 fiber volume in carbon. Under special requirements, we would even go above those numbers. As you can see, Eric's dismal painting (39% for glass) was far less than where my brain was wrapped.

    I would love to use those techniques. With all us engineers and technicians (with our gear-head hobbies) and if that company allowed us to make things on the side, every autoclave in every building would be running 24/7 building our yachts, cars, planes and 15 million other things!

    Since you sell the materials (for a boat) like a kit ($35K). Do you also build them? If so, what would be ROM (meaning off the top of your head… I’m years away from that option) type number for building one of those 50’ ready to sail? Is it possible to get someone to sail it to say… US gulf coast somewhere and how much would that be? And do you have any more conventional designs available? I just looked at those harryproa boats that go both ways… it may be the next coming(/going), but I’d have to let that trend pass by me. Although, I'm going to have to look at it in more detail... interesting!

    P.S.
    Yes, it was you stewi... I didn't want to give you credit/blame/fan mail without your consent.
     
  8. chandler
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    chandler Senior Member

    90# for a hollow timber mast. It's going to be stayed anyway. Sounds like a no brainer to me. Rot in the mast? You going to leave it on the ground in a swamp in the off season??
     
  9. Robjl
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    Robjl Senior Member

    Stewi, the mould suggested would be a half of the oval section, plus a bit. I would use this to make up sections to join up to a complete mast core... this core would be the minimum thickness that would hold it's shape (on about 4 supports). The bulk of the layup would then go on top of this core and it becomes part of the mast.
    Inquisitor;
    Structural properties with disclaimer:
    "mechanical properties for E-glass epoxy
    laminates, based on a 50% fibre-fraction by weight. It should be noted, these
    properties will change with varying fibre-fraction, as well
    as epoxy system used, these values are not provided as specification, and testing of
    cured laminate mechanical properties should be
    completed prior to design / structural analysis of any component.

    unidirectional
    thickness = 0.104 mm per 100gm/m2 of reinforcement
    tensile strength = 490 MPa
    compressive strength = 390 MPa
    flexural strength = 530 MPa
    modulus = 24,800 MPa

    biaxial (0/90)
    thickness = 0.114 mm per 100gm/m2 of reinforcement
    tensile strength = 275 MPa
    compressive strength = 220 MPa
    flexural strength = 372 MPa
    modulus = 15,520 MPa

    double-bias (+45/-45) - at 45 degree to the fibre
    thickness = 0.114 mm per 100gm/m2 of reinforcement
    tensile strength = 86 MPa
    compressive strength = 84 MPa
    flexural strength = 86 MPa
    modulus = 9,650 MPa "


    I hope this allows for some decisions>>:?:
    Regards
    Rob L.
     
  10. Inquisitor
    Joined: Nov 2005
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    Inquisitor BIG ENGINES: Silos today... Barn Door tomorrow!

    Never say die!

    Walking Through the Analysis.

    • Open the attached spreadsheet “Mast Study HL.xls” (Hand Lay-up)
    • Scroll down to Section 4. You’ll note that I’ve now added the metric conversions so you and the rest of the world can work the spreadsheet without abuse. Nominally, you should change the blue items.
    • You’ll see I have your proposed 50% larger mast and the Priestess’ (assuming your source) stiffness and strength numbers.
    • I have estimated the material density value in (D45). It does not affect the stress analysis, but it does affect the weight estimation. You might want to get an actual material density value.
    • I then fiddled with the zero degree ply thickness (D50) until the margins in red were all at least 1.0
    • Using Eric’s suggestion about the outside ply, I suggest a laminate of [45b/0b/0u/0b/45b]T
    • The subscript “b” is her biaxial weave cloth. I found a representative fabric weight of 5.6 oz/yd^2. Converting to metric and using her 114 mm/ (100gm/m2) conversion, I got a ply thickness of 0.15mm (0.0059”)
    • The subscript “u” is her unidirectional material. It needs to be 3.59 mm that we got from the spreadsheet.
    • This results in a laminate with 86% zeros. I’ve seen that high in AE applications, but you might want to double check with the priestess and see how she feels about it. If not, see how high she’d go and I can run those numbers.
    • I then used an LPT program to calculate stiffness and strength for this proposed laminate.
    Modulus = 23.3 GPa (3.38 Msi)
    Compression Strength = 383 MPa (55.6 Ksi)
    Thickness = 4.19 mm​
    • The spreadsheet “Mast Study HL2.xls” plugs these numbers back in.
    • Note the composite weight is 25% lighter than the aluminum mast. (NOTE: This is the total laminate, but with the estimated density. It is also NOT TAPERED OR WITH CROSS SECTION VARIATIONS). Improvements can still be made.
    I want to re-iterate the failure modes and the results of this second spreadsheet.

    Compressive Failure – This is where you take a piece of chalk and hit it with a hammer. Things come to pieces. This mode of failure in composites needs to have the priestess’ safety factor (SF) of 5.5. We show a “margin” of 2.12. This means we have a SF 2.12 times whatever the SF already in the aluminum mast. So if the aluminum mast has a 2.6 or higher SF, the composite mast will have at least a 5.5 SF.

    Euler Buckling – This is where we take a soda straw and put a finger on each end and press together. Things don’t come to pieces, it just buckles. A composite mast failing this way will bow out and if the load doesn’t let up it will finally break in two… probably near mid span between spreaders. The good thing about this one is it is totally dependent on stiffness and tube geometry. Composite stiffness properties do not vary as badly as strength properties and thus the SF related to stiffness is typically smaller. You might want to get a second opinion on that one. Since the margins are 1.09, we have only a 10% larger SF than the aluminum mast.

    Wall Buckling – This is where you take a Fosters’ Oil Can and crush it. If done correctly, it has a nice regular pattern and the top ring is right on top of the bottom ring. The wall on this mast is pretty thin. You have several options. (1) Build a meter long section and crush it and see if it fails like a Fosters or like chalk. Unfortunately, a composite tube failing with wall buckling splinters to pieces like the chalk anyway. The only difference is that if it fails before the 130 tons of theoretical strength, then it failed by wall buckling, if it makes it above 130 tons, its most likely failing in strength. If you actually have some way of applying this much load, you might want to get it strain-gaged. If you don’t have access to the equipment to record strains, you could go the low-tech method. Put a dial indicator between the ends of the meter long mast and video tape the dial indicator and pressure gage on the hydraulics and we can back out load, strength and modulus. If wall buckling is an issue, structure will have to be added somehow. There are many options.

    I saw that you want the mast to be hollow. I need to ask, the lines running inside, will they be only rope or will they be cables or have any other metallic items banging away on the inside. I can just imagine cable grinding away the interior plies or metal rings banging away. How many conduits were you planning for the aluminum mast? (One for electrical, one for each line or one for all lines).

    Making Decisions
    I think you have to decide what your goals are.

    • It is lighter (unless local buckling or conduits drive up the weight)
    • It is stiffer in bending than the Aluminum mast
    • It is stronger than the Aluminum mast. If the SF of the Aluminum mast is at least 2.6 then we are even higher than the Priestess’ 5.5 S.F.
    Although, your method of fabrication seems feasible (broken record) I strongly suggest that the zero degree plies must have no waviness. Please consider some way of tensioning the zero degree fibers during cure. Check my post #29 or Stewi’s #32.

    Highlights…

    1. Your circumference is ~1 meter.
    2. Create a panel 1 meter long and 2 meters wide.
    3. Stretch the zero degree plies over the 1 meter direction.
    4. There total thickness of the zero degree plies must be no less than 1.795 mm (1/2 the total)
    5. Squeegee the hell out of it, but make sure the tension is keeping them absolutely strait. Apply the 0.15mm 0/90 cloth and then the 0.15 mm 45/-45 cloth. Don’t add resin to these two plies. Vacuum bag and let cure while stretching. Bagging while under tension without letting air in will be a challenge. Let the two cloth layers act as bleeder cloth. At the very least, it will improve the fiber volume. See figure 1.
    6. After curing, cut the panel in half in the zero degree direction.
    7. Ban saw your mast interior cross section out of foam of say 300 mm long. Bread-slice it into 3 equal pieces. Numbers are Wild *** Guess (WAG) You’ll probably have a far better feel when you feel the bending stiffnes of the laminate. More or less ribs. Thicker or thinner ribs.
    8. Use the thin-walled PVC pipe for conduit(s) and
    9. Assemble it like a plane wing… spars, ribs and skins. See figure 2.
    10. The first panel should be bonded (with the off-axis plies on the inside) to the ribs with the seam clocked around say the 45 degree point. (still need to rationalize this seem some.)
    11. The second panel should be bonded with the off axis plies outward and the seam 180 degree around.

    With this as a baseline, you’ll have a beautiful outside ready to paint and if we need more local buckling strength, we can put a thin (WAG 5 mm) foam core between the panels… That’ totally eliminate any local buckling problems.
     

    Attached Files:

  11. Robjl
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    Robjl Senior Member

    Inquisitor,
    The penny has dropped> I get numbers now....sorry but when I guestimated a 50% area increase (based on a comparison of the figures I had for alloy & GE) in cross section I should have said... "a 50% increase in cross section area" (thickness) . Bad mistake.
    When I try the 240 x160 size on the spreadsheet it just doesn't work as hoped.
    But I still don't get it? The comparative strengths of the two materials doesn't seem that far apart? or is it the stiffness that's the weakness for the GE?
    My guess is that we need a greater SF for a composite than Alloy.
    Spreader bases are usually fitted with a through bolt and a "compression tube" (= a tube inside the mast, the through bolt goes through it. The ends of the tube bear against the inside wall of the mast to prevent it from collapsing)
    The lines inside the mast,
    Topping lift (holds the outer end of the boom up)
    Halyards for raising sails
    Some may be part wire (SS 7x19)
    I have in the past fitted a wooden block inside the mast , just above the lower spreaders. The block has a hole about 70mm diameter through it with a plastic (acetal) wear liner. The halyards therefore (when tight) don't chafe the mast interior and most important don't rattle and keep you awake at night.
    The goals are changing as the options narrow.
    I don't think a mast significantly larger in outside size than the alloy is worthwhile. Windage is just too important.
    The weight is not so critical but EG shouldn't be heavier.
    Tapering is worthwhile as is localised strengthening. Consider that the Alloy mast has constant wall thickness. Shouldn't the EG with equal strength to the alloy but with increased thickness around holes and load points (add 50% thickness to these points only) give us the greater SF reqd for a composite?
    Interested in your fabrication ideas...I'll digest that for a while.
    Regards to all.
    Rob
     
  12. Robjl
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    Robjl Senior Member

    Hanging on by a thread...

    Inqiusitor,
    Does the spreadsheet consider the mast as panels? The max panel compression load will be on the bottom panel 6.5 metres long.?
    Does Euler consider the buckling load over 17 metre or 6.5metre?
    Only one conduit is needed.
    See-ya.
     
  13. Inquisitor
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    Inquisitor BIG ENGINES: Silos today... Barn Door tomorrow!

    There are three failure modes possible. Only one is based on the strength of the material. But as you see in the spreadsheet the Compression Strength analysis (B57) is not really an issue. 167 tons would drive the mast through your hull long before the mast failed in this mode.

    The other two failure modes are entirely driven by stiffness! Carbon’s stiffness (being 3 times stiffer than glass) can only (reasonably) be overcome by increasing diameter. If you want the same diameters…
    ...its a shame, but glass's strength has nothing to do with it. The thickness you are looking requires a better than 200% weight increase. Not really practical.

    I re-read your post #3 and I can see that it can be interpreted both ways and I jumped the wrong way. My mistake! :eek:

    I lost over half the stiffness going from AE's 78% FV to Marine's 39% FV

    I would lose another two/thirds of the stiffness trying to use the same diameters as the aluminum mast.

    It would require radical AE analysis techniques. I (me versus the company's) only recently have acquired enough computing power to be able to handle the level of analysis you now would require. It would require a rather in-depth finite element analysis… probably several models including an overall mast model and several detailed models of key joints. I’m quite capable of doing this kind of analysis (did it for years) I would also have to have the loads at every mast mount, stay, shroud, spreader and sail traveler load for every wind condition. Including shock loads. I would have to do a battery of tests to get "real" properties for actual hand lay-up. I'd have to do a lot of them to get the statistics up enough to be able to decrease the S.F. to the bone. If I could work on it full time for six to a year months, I probably could still design a “serviceable” mast out of glass.

    Unfortunately, for all that time and effort all we would have is a mast that is only mediocre in performance, near as heavy as aluminum and would be specialized for your boat only.

    Sorry :( I will now have to side with the rest... it can't be done with glass/epoxy.
     
  14. Inquisitor
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    Inquisitor BIG ENGINES: Silos today... Barn Door tomorrow!

    Currently, the spreadsheet only mimics the aluminum mast. It would be as strong in Euler buckling in any condition that the aluminum mast is.

    If a detailed analysis (with actual loads) were considered, it would be done for each of the panels (between spreaders). The spreadsheet does not go to that level of analysis.
     

  15. Robjl
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    Robjl Senior Member

    Only one fibre left in the thread...

    Inquisitor,
    You last post sounded like you were using 37% fibre volume....?
    I think we can achieve 50%; particularly with the unidirectional 55%.
    Does this help?
    Many thanks,
    Rob
     
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