Carbon Fibre Masts

My boat will be minimal 45 - 50 ft - maybe even 60. In such a case figures tend to change - read increase - dramatically.
I am waiting for the first available tests of a new alu alloy that is about 4# stronger than the regular AlMg 4.5 or Alustar AlMg 6 and extremely corrosion-resistant.

If it will not become commercially available, then I will opt for my own composite design after I have done some practice testing regarding to the weight properties. Another idea might be the development of a titanium woven inside the carbon lay-up as reinforcement like steel mesh in a ferrocement configuration. But then of a denser nature.

Nobody in the yachting world goes beyond full live testing. Even Alustar, an aluminium alloy that already existed in the FRS since long, had to be "tested"before it was approved as a hull construction material.

There are lots of known techniques unknown in yachting but nevertheless very useful if you are familiar with their existence and apllication.

I will give you a simple example: have you ever been aware of Teflon Impregnated Aluminium? And what the effects are in real time, so to speak?

 

Titanium use in Mast

That's one of the questions I was eluding to in our private conversation about the titanium material....what possible use it might have as a mast material, and in particular on my unusual rig??

A very IMPORTANT consideration in any hybrid situation such as this would be the bonding material/strength between the two different materials and their relative independent strengths. Often one of the materials takes up the great majority of the initial load and yet is 'undersized' in the belief that it will receive its extra load ability by the other attached material. This works sometimes, but in other instances it creates too much of a load on the bonding material which fails and thus throws the load to the now two independent materials, neither of which are sized to carry the load.

A prime example can be found in the selective use of some amounts of carbon fiber reinforcement on otherwise fiberglass boats. In the belief that this small carbon addition will substitute for some number of addition glass layers, the glass structure is cut back as a result of the added carbon. But the small amount of carbon then comes under load first, and then fails as it is insufficient by itself. Next the glass structure comes under load, but fails as it is insufficient as well, in the belief that the carbon would help with the job.

I'm not 'nixing' the idea at all. I just want to do a thorough analysis before commiting to such an idea. I have done some thinking along these lines of selectively reinforcing alum mast with glass of sorts, but not arrived at a satisfactory conclusion yet.

Have a look at this discussion of Composite Masts. Eric Sponberg comments, "Also, when combining carbon with wood, carbon is very much stronger and stiffer than the wood simply in raw numbers (ignoring for a moment the specific strength and stiffness when divided by the weight), and the loads on the mast will be carried by the stiffer material in direct proportion to their relative moduli (material stiffness). That is to say, if you put only a little bit of carbon over the wood, the loading in the mast will want to carry through the carbon much more readily than through the wood, because of the differences in their stiffnesses. There is a chance that the thin carbon laminate could be quickly overloaded and fracture. The load would then transfer to the wood, which if undersized, would also fail quickly.

 

brian eiland quoting Eric Sponberg: ... carbon is very much stronger and stiffer than the wood ..., and the loads on the mast will be carried by the stiffer material in direct proportion to their relative moduli (material stiffness). ... the loading in the mast will want to carry through the carbon much more readily than through the wood, because of the differences in their stiffnesses. There is a chance that the thin carbon laminate could be quickly overloaded and fracture. The load would then transfer to the wood, which if undersized, would also fail quickly.

Exactly. I couldn't agree more. I've always thought the carbon mast was similar in nature to what I originally thought glass sandwich hulls were: overly brittle construction, based on the "hope & pray" theory that the stucture won't be pushed too far, and even if it is, that just means the manufacturer gets to sell more replacements.

 

The fact is Brian, that I have wandered in metallurgy the last 10 years. If I touch the titanium issue, everybody wants to supply some pennies without having a single trace of knowledge about the material itself.
In this respect, titanium is simlar to epoxy - epoxy comes in a host of formulae's nontheless everybody discusses epoxy as being an element instead of a mix of different chemical components, that can be adjusted to purpose.
Titanium is only valuable through it's alloys. The basic element has no better properties than mild steel. The basic raw material is nothing compared to the final alloy.

I know that you are open minded and therefore I am not too prudent to ventilate some ideas I have without being mocked on.

BTW, you were talking about your aft rig. In the attic I have a modelship, that I made 10 years ago with the mast at 1.50 mtrs distance from the stern and the keel positioned just behind it. There I stopped, and did other things till I saw that idea based in your catamaran configuration. So I thought: I am not the only one playing with such an idea. I had no further interest to pursue the idea because it requires serious testing and I was not up to that.

With the titanium mast issue it's another situation. In the first place, if I want to do some testing, I have the means to do that. I have access to the material that I want and secondly, I am not pursuing a commercial target.
If it works, it works for me. The rest I don't care about.

There are lots of disadvantages connected to the treatment of titanium. No amateur ever can afford to use it and to apply it, and therefore I don't advocate it.

I have some compostions of 318, AMS 4928F and TU 9-623-87; TV 92 that I will mail to you and Eric Sponberg. When you see the properties you may draw your own conclusions.

Back to the mast issue: the titanium inlay alone is strong enough to replace the original alu mast; The outside layer of carbon is just to stabilise it; to add more stiffness, if required and where required. As I say, it is a development of an idea that I had when the issue of Titania's building came up.

We can even go one step further in metallurgy. Next to Titanium are the Boron alloys. They have even superior properties than titanium, but are not available in commercial quantities. It has the same weight or even less as Alu and is 16 times stronger - generally speaking.

Do you know that you can weld aluminium to titanium without any problem?

Cheerio,
Brien

 

What does this imply about the working lifetime of an aluminum mast? I read today (on another board) comments on the Kirby 30 saying they had a high rate of dismastings in a way that did NOT imply that attention to rigging, spreaders, chainplates, etc. would have prevented the problems.

 

Nothing negative, the boat I recently procured has still its original masts, single spreaders, but still ok. And 35 years old. I know also a few wooden oldies with their original masts, also wood, dating back from1934). We are just exploring new possibilities - masts that are still to be found on the more expensive yachts.

 

sometimes it is not only a matter of tensile strength

hi guys
the argument is right for most application, but talking of mast, I have to say that sometimes carbon has been conbined with wood not for tensile pourposes but for buckling problems. indeed, wood stripping helped a lot of catamaran hulls and wingmasts to prevent from buckling either in a true sandwich configuration but also and more often like a straight single carbon laminate over wood especially in wingmasts, in this case carbon epoxy would take all of the load, while wood and especially its thickness prevent from buckling the very very thin laminate

cheers
Marco

 

This thought is for all lovers of bonding 2 dissimilar materials together. Different linear thermal expansion rates, do length AND diameter. I have a strong gut feeling Titanium expands much faster than a carbon based material. If so, black outer surface will conduct a hot sunny days heat into the sealed metal tube. POW. - 10 degrees F causes a mid winter explosion in the tube. I am not the ME. Look up the expansion rates of a 40' mast for the 2 over the temperature extremes world wide. Sailing combined with storage in the tropics. + 150 mast in ceiling of shed, to - 20 in Canada. Any one material, metal no problem.

 

Eric

I wince at that.
The problem (as I am sure you are well aware with this method of construction) has been predicting accurately the stresses to be countered.

As I said if you build for insurance you end up with the material close to the weight of Al and I add; at 3 times the cost.

Fatigue strenth for the composite with axial fibre loads is as you say very good but with any non isotropic material the fatigue strength for unpredicted loads not countered with accurate fibre placement is abysmal. Your figures on fatigue may mislead people unaware of how and what affects fatigue strength and what you count as a fatigue cycle.

Note that the Americas cup boats have CF masts very well engineered by very experienced firms yet they exhibit catastrophic failure. More recently the mast failure on the winning Sydney-Hobart after the fatiguing stresses of the race (presumably). I say presumably because the big problem is forensic enginnering on shards of mast after catastrophic failure. How do you work out the failure mode? was it local buckling? fibre tensile failure? fatigue fracture? Production fault.

I am sure that eventually the material will become acceptable to conservative designers around the globe when enough experience has been had to produce some decent scantling rules. Acceptance worldwide will need common high quality automated production processes , perhaps a more standardised global fibre rating, and a drop in price.

I am also interested to se the longevity of this material compared with Aluminium.

I admit the light weight suits the modern light weight vessels, but on heavier displacement long distance cruising boats I am far from convinced that the extra cost is anything like justified.

I am also worried about the retro fitting of light rigs into boats that will suffer from low roll inertia.

We all have our foibles

Jutson has a good article on CF worth reading
http://www.jutson.com/contents/articles/aug98.html

 

With my titanium-carbon compo system, I wasn't far out of track, this being within financial limits, it is presently superseded by a method to coat carbonfibers with Boron (a high tech extremely rare metal); that results in a material that has twice the strength properties of HS Carbon.
It is used, caused by the high manufacturing costs, only in aerospace and tennisrackets.

Richard, titanium does not expand faster than carbon does; furthermore, bonding dissimilar materials are executed with a high rate of success: in concrete (mortar, gravel and a steel reinforcement) in FRP - I may ussume that you are familiar with this material, car tyres, (steel or kevlar belted) etc. etc. In fact, titanium transfers heat very badly. I know that for a fact.

That a carbon mast gives way, is related to its very complicated construction with materials that are not fully developed yet. See it as lessons that has to be learned and paid for in order to get later on a better product.
Also the variety of loads may rise to unknown properties and the risk of mastbreaking at maxi-yacht level is factor X times the normal applications, where the loads can be relatively better calculated and do not run in extreme figures.

 

Coating Hi-Tech Fibers

Please forgive my ignorance, but wasn't the coating of hi-tech fibers done to promote the bonding of them in the resin matrix?? Was that for kevlar, or carbon, whatever?, I've forgotten, but I seem to remember there were significant problems getting a proper bond between the fibers of some materials and the epoxy or vinylester resins. Without a proper bond the two materials seperate and must support any load as two entities rather than a single stronge substance.

Also can a 'coating' of the carbon with boron, rather than a 'mixing' in the molecular matrix of the carbon really increase its strength so significantly??

 

No, you are correct in your reference to kevlar, I am not aware of any problems in bonding carbon. Actually on the contrary.
I got a roll of Aeronautical quality carbon fiber when I was in the plant of Messerschmidt in Augsburg. It was amongst all used in the construction of the Tornado, in any case my sister wanted a hunting bow so I made one out of Zebrano, Hickory and pieces of that particular Carbon. I bonded it with SP (my favorite epoxy) and today, after so many years of severe use in our forests, not a single problem with delamination. The bow pulls is more that 70 pounds so you can imagine what power comes loose. If carbon was viable to delaminate, it would have taken place already long time ago the bow is more than 12 years old.
Kevlar had severe bonding problems when in the late 80's it was used on a larger than one-off scale. When the bonding problems became known to DuPont, they used special coatings on the Kevlar to improve bonding properties and today, it is a well accepted material to use in boatbuilding.

The Boron coating process is a new one that I just discovered and to complete the info I have to get more about the specific coating process.
To answer your question about Boron coated carbon I don't know enough about the mfg process but I believe the particular bulletin becaus it comes from a very reliable source. If I get particulars I'll publish them.

 

I guess I have to chime in again.

I look forward to receiving more information from D'Artois about his carbon and Titanium mix.

As far as thermal expansion is concerned, carbon fiber laminates have a negative coefficient of thermal expansion--as they cool they expand, and as they heat up they contract. That is why with the right mix of materials in the laminate, they can be made to have little to no expansion/contraction whatsoever, and that is why carbon fiber laminates are so useful for space vehicles--because they don't change shape as they travel from the warm earth to the cold of space.

As for masts on high tech boats like the America's Cup, remember that such boats are built with very little safety factor. The ideal AmCup boat will completely disintegrate two seconds after crossing the final finish line for the win. If there is too much weight in the boat, you are wasting money and tactical advantage. (If you are not living on the edge, you are taking up too much space.)

Cruising boats, on the other hand, typically incorporate factors of safety over predicted breaking loads of 3 or 4. I certainly do this in my free-standing mast designs, and with over 25 years of designing such masts, I have never had one of my designs, that I am aware of, fail on account of fatigue or being too lightly built. Are they overbuilt? I don't think so, I think they are reasonably built. On Wobegone Daze (modified Freedom 38 cat ketch) the new wingmasts weigh about 240 to 280 pounds each--is this too heavy for the design? In my opinion, no. I don't need to make it heavier, and I certainly don't want to make it any lighter. And this boat has been offshore from Newport to Bermuda, and a couple of times offshore from Marblehead to Halifax, Nova Scotia.

As for the nature of failures, I have had many occasions to actually make some full-size composite tubes (fiberglass as well as carbon for a composite flagpole manufacturer and client) in order to determine the mode of failure and level of ultimate stress. They all fail catastrophically (that is, there is no "yield point" to indicate impending failure--composites are brittle). Composite tubes such as the flagpoles, and free-standing masts, almost always fail on the compression side, and if the wall thickness is too thin, local buckling plays an important factor. This is why wall thickness in relation to diameter is so important, and many people who engineer composite masts don't realize this or take it into account. Local buckling is why I almost always try to incorporate a shear web into my wingmast designs (A client and I are trialing a new design this year without a shear web to see how well it behaves.) A mast will not last long if the side walls are moving. It is essential that the section shape be designed to maintain its geometry under load. Buckling occurs when the section shape starts to collapse--then there is no hope for survival.

Finally, from other design research that I was able to do many years ago, composites of all types exhibit three modes of microscopic failure, the worst of which leads to catastrophic failure. The first mode of failure is the breaking of the resin between fibers. A composite can withstand a lot of this type of fracture and not lose overall strength.

The second mode of failure is the breaking of the bond of the resin to the fiber. This takes more energy, but again, a composite can withstand a considerable amount this type of fracture and still not lose overall strength.

The third mode of failure is when the fibers themselves break. This leads to permanent degradation (fatigue) of the laminate and directly to ultimate failure. You never want to reach this point. And typically, fiber breakage usually occurs at about 50% of the ultimate breaking load of the laminate. Therefore, you want to be sure that your live loads never exceed 50% of ultimate, so that the minimum factor of safety is 2.

On my mast designs, I make sure that my projected live loads (at maximum righting moment of the boat) never exceed 1/3 of the ultimate breaking strength (factor of safety of 3), and as I say, I have never known one of my mast designs to fail due to overloading, fatigue, or buckling.

On an AmCup boat, however, or on a grand prix type of yacht, where the factors of safety are very much smaller (less than 2), you can expect that the masts are not going to last too long. But most synidicates and owners realize this and accept it (If you are not living on the edge....). Of course, such a situation is not acceptable to the cruising sailor. But at the same time, carbon fiber masts can be made with acceptable factors of safety and acceptable weight, that are still lighter than aluminum, and do last a long time.

Eric

 

Eric
Thanks for your comprehensive reply.

I agree there is no factor of safety in the America's cup boats, but I have talked with some of the mast design engineers who were alarmed at how poor (and unreliable) the FEA analysis had been, so I guess my problem is that if we can't use our tools to analyse a complex non isotropic material under stress then the conservative engineering approach is to specify a material for which we can predict its behaviour.

A safety factor of 3 gives a bit of leaway . In Australia the cost would be too high, by the time it gets cheaper it will hopefully be a tried and true material.

You appear to have been something of a pioneer in this area. Have you published any papers on CF mast design ? If so I would be interested to read them.

Just off the top of my head, you could experiment with introducing some pre-stress by pressurising the mast, and shifting the curve. I am sure you could throw a lot of $$ at research here.

 

G'day,

Carbon masts do not need to be expensive. I built a 12m/40' unstayed mast for my 12m proa. Carbon and resin came to under $Aus1,500/$US1,100. There were a number of things which made this possible

Use carbon tow which is the material that cloth is wooven from. Costs $US7/lb.

Do not use prepregs. There are now long outlife, low cure temperature epoxies which are as good or better than expensive prepregs. I use an ATL resin costing $Aus13/kg, or $Us5.45/lb

Do not use expensive moulds. I built mine from mdf. The carbon strips tapered in width and thickness and were vacuumed at 2 atmospheres pressure. Resin fibre ratios are as good as with prepregs at much higher pressures.

The downside is that you use a bit of bog to clean up the strips, which adds marginally to the weight. It also takes a while to build, but the work is very simple.

For a more detailed explanation and some pics, have a look at http://www.harryproa.com/building_hg/buildinghg_wk14.htm andhttp://www.harryproa.com/building_hg/buildinghg_wk15.htm

We have since improved the technique and are now building carbon masts considerably cheaper than anyone else we know of. Unfortunately, this technique does not lend itself to amateur use.

Regards,

Rob