I got your attention now ehh guys !

"Carbon is for lazy engineers"

as in what a pocket calculator was for a student today who checked my claim that 35 times 37 wasn't 1645 (the answer he wrote down in his paper).

Lets, see if you guys are smart enough to figure that one out under 1 sec ?


Also I haven't seen too many carbon fibre dolphinstriker straps, surely this doesn't have anything do with the "superior" stiffness or tensile strength of carbon laminate would it ? That is if it has such superior qualities.

Ordinary stainless steel will kick carbon's butt in these area's, my friends. Just ask Goran Marstom who is now replacing all the carbon stays and trap lines on the M20 for plain stainless steel.

Also simple oak wood will kick carbon's butt in the low density department, being twice as low. There is a 600 years old oak beam holding up the ceiling at the old Hijink family farm. I want to see the glue in the carbon-epoxy matrix see do that.

Now lets combine these two materials in a composite boom. Composite in this phrase used in it original meaning = "made up of different materials" and not in its current slang meaning = "GRP" or "CRP"


It is just like I said boys :

Carbon is ONLY attractive when a designer is seriously limited in the volume AND weight he can accept for a given element. If either one of these is NOT limited then their is no reason to spend more money on carbon as a simple adjustment of the design will result in exactly the same performance.

When a given modern engineer doesn't know what to do, he then appeals to the devine status that carbon seems to enjoy in todays society to get himself of the hook.

Anybody else noticed some people exhibit a Pawlov reaction when some poster discusses the issues he has with a given setup or component ?



You've bend an alu boom ? Buy a 350 dollar carbon boom.

Your boom flexes under load ? Well just order a 600 bucks custom job at your local carbon shrine.

Can't right your Nacra 5.5 singlehandedly ? Well, the solution to your problem is a 4000 US$ Hall spars carbon mast.

Want a good singlehander ? Buy the latest 20.000 US$ A-cat and then learn to bitch about its PN handicap and the fact that everybody is buying 14.000 US$ spi equipped FAD boats.

I remember last time, when "my boom flexes" Dave Farmer broke his mast, that the first advice was again that he should not attempt repairing it but just order a new carbon mast.


Lets face it guys, for some of you carbon has become a religion.

As in the answer to all things, being beyond question and scientific analysis.


Me personally, I've developped an allergy to carbo, I've seen it abused too often. The only density reduction the use of carbon achieved effectively in my situation was that of my wallet. <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Wouter

You are right here.

The main line of though I'm following now is that I don't feel that there are big loads on the in te sideways direction. So no material is really needed here. Neither stiff nor much of it. But their should be enough to prevent the boom from buckling or breaking in case it hits the stays or something else.

If there are any real loadings on the boom I suspect it is almost exclusively in the vertical place and mostly in the rear part of the boom. To check this I want to know how the current boom flexes.

Lets stick to your T-shaped boom for now, to keep things simple.





In the diagram above I've draw the forces that I suspect are dominant, that cause the flexing.

The black line gives the level of bending stresses inside of the beam. Clearly around the mainsheet point the internal bending moments are the largest. These reduce down to zero towards the ends. The internal shear forces are not drawn, but these are rather small (and constant) in the front part of the boom. In the small rear part these are significantly higher but still constant. I suspect that a decently thick planck will be able to transmit these shear forces, but reall calculations need to be performed here.

Clear the bending loads are not constant along the boom and so it pays to give the boom different crossections at different points along the boom. The wood is most there to act as spacers between the strip of alu or stainless steel on the top and bottom. These two strips take by far the most of the bending loads. The wood middle part handles the shear stresses.

The drawing on the bottom is the top view. Clearly I made the boom thicker in the middle and narrower at the ends. Clearly a cosntant crossection boom will be weakest in the middle so I've compensated for this by moving some material from the end to the middle. The wood will be strong enough to take any loads in this place, because they won't be very high.

You can just cut the top (horizontal) and bottom (vertical) planck by the outline and then cut out smaller sections to save weight (circles). You can attach the top strip with the top planck to the bottom plank by just screwing through all these sections with woodscrews. Some timber glue may well help but is may not be necessary. Now you only need to fold the bottom strip along the bottom contour and secure that with screws as well and the boom is ready to take the fittings.

By the way, I forgot to draw the rear section taking the traveller rail. Just adjust the outline of the bottom planck to get the right angle for the rail. Here I would put a U-shape metal strip over the bottom and secure that side-ways to the plank by schrews. Fit the rail to this additional U-shaped section. This should transmit the loads better to the plank.

The cut-outs need to be well places to save weight and not degrade stiffness and strength to much. You can buy saw-bits that can be mounted to your drill or simply saw out hexagonal shapes with a suitable blade. Both will work. This way of building the boom will be both easy and fast. Most likely it will be cheap as well. You can test the setup using some old planks you got in your shed and a section of alu strips (hardware stores). You can then test this and determine how it performance and adjust the setup.

Remember, wood like Douglas Fir have only 28 % of the density of carbon laminate. Meaning you can use 3.6 times as much (in volume) as you can in carbon for the same overall weight. This makes the boom alot more stable under load as here volume is just as important as material stiffness. Yield stress of these wood types are still at 55 % of that of aluminium. But aluminium is again 5 times more dense meaning that the wood per USED VOLUME can carry more load then aluminium ! This makes wood a very attractive material to make the main body of the boom from. Here you need volume for stability BUT you DON'T to want to accept much weight here.

A strip of stainless steel is 10 times as stiff per volume as the same volume Aluminium and about 7 times as stiff as a normal carbon laminate of the same volume. By the way stainless only weights 3 times as much as alu and only 4 times as much as carbon laminate. So stainless steel is what you want for the strips (like a on a dolphin striker strap), but it is expensive. Alu is dirt cheap. Carbon is hardly more interesting then alu (in the way of stiffness per volume (only 30 % more) and very much more expensive. So it will be either stainless or alu. Added advantage is that both metals are easier to work with. Just bend them around the slightly curved contour and screw them to the planck. You can finish the boom and sail away minutes later. No sticky fingers, curing time or chemical lungs.

Both the bottom contour and side contours are slight curved.

Now I want to see any constant carbon crossection even beat this simple wood/metal setup both in stiffness, strength AND weight. More is possible if we spend some more time optimizing the design.


Wouter

Rolf:

Having sailed a Hobie 16 with asymmetrical hulls and now a Hobie 17 with symmetrical hulls. I say the symmetrical sail a LOT smoother. It seems to have a better feel to me, especially going downwind. But the centerboards may have something to do with it too.

Dou Snell

Rolf,
I've had an TheMightyHobie18 Magnum, and still have a SC20 with symmetrical boards, and Flight Risk just points substantially higher. If I pick out a point on shore as I'm heading in, and attempt to maintain a straight course, I can see the boat working to windward. Have done windward leeward with J boats and 35' racer/cruisers and I can either point as high as they at their upwind speed, or bear off 10 degrees and beat them handily to the windward mark, in less that 10 kts of wind. My other boats (admittedly in my hands) haven't performed that well. The difference seems very noticable to me, though I doubt I'm as sensitive as you experienced racers. So I'm puzzled that they aren't tried more commonly. It may be that the required switching of the boards with each tack/jibe is too much hassle or time, for racing. Pretty fabulous for long tacks/reaches though. Having the "wrong" board down works well pulling the boat to leeward on downwind runs too.

Dave

Bill,
Yeah, I like the curved traveller a lot, though it would be tough/expensive to retrofit this boat with one. The current system provides the same constant downforce on the clew, even when the clew is not directly over the mainsheet. And I can see that not having those 2 line up will stress the boom more than a direct connection between mainsheet and clew. But I think I'm committed to this system, and I don't think it'll be difficult to build a boom that can easily handle the forces generated by the misalignment of clew and mainsheet.
I think the major compression forces are produced by the outhaul resisting the desire of the clew to move forward(towards the mast) when pressure is applied to the body of the sail. Without the outhaul pressure the sail would want to bag out to leeward, which would entail the clew moving forward. This was very noticable on the original main of the Reynolds 21, which was boomless. When it blew over 15 kts, it bagged seriously, even with the mainsheet attached the the furthest forward hole in the clew plate. How does the N 6.0 get around that?
Thanks for the input, I'm still trying to come up with clear pictures of the forces involved here, and it reall y helps to get a bunch of different perspectives!

Dave
And all of this is theoretical, it's clear that there are signifcant compression forces here, evidenced by the flexing experienced.

That is not the only possible conclusion that can be drawn.

The boom could well be under hardly any compressional loads at all and be flexed by bending moments. This situation is actually far more likely.

Wouter

See the attached screen dump of an excel sheet. It shows the automated calculations that produce an aluminium round tube with the exact same (bending) stiffness AND weight as a given round tube made out of carbon laminate.



All the numbers given in blue can be modified at random and an equivalent tube will be produced. This mathematic problem is fully determined, meaning that a solution (of equivalence) can ALWAYS be found. Although it must be said that not all produced wall thicknesses and outer diameters may be realistic because of other engineer considerations. Example ; a wallthickness of 0.1 mm is impossible to achieve by extrusion, a common production method for alu tubes.

The excel sheet allows all kinds of materials to be entered.

In the screen dump I've entered the typical material property values for aluminium and carbon laminate. A little further down I defined what could be typical dimensions of a carbon A-cat boom (0.04 x 0.002 mtr.). Clearly a fully equivalent boom can be produced in aluminium, both in weight and stiffness, when the extrusion has the dimensions 0.059 x 0.001 mtr

How stupid is this ?


For obvious reasons I left out cost-equivalence.

Obviously some mathematical model needed to be developped that could easily produce these results. Good engineers will do that, lazy engineers will just just think "whatever" and try to solve the design problem by throwing lots of money at it, covering their lack of skill by using exotic materials.


For reader who are interested in learning something more. The closer two materials are in their stiffness and density ratio the easier it is to produce an equivalent beam in both stiffness and weight. Pretty much any a-symmetry ratio (R_E/R_Ro) that is close to 100 % will make the use of one material over another unimportant. That is unless other considerations like cost, ease of production and stability of thin walls are not factored in. This a-symmetry ratio between aluminium and carbon is not particulary far from 100 %. This leads to the situation where it is relatively easy to find good alu alternatives to carbon laminates. A similar analysis can be performed for glass and kevlar fibres with respect to carbon.


A counter example : Lets compare dyneema lines to stainless steel cables. The asymmetry ratio is now about 700 %. Makes the carbon/alu ratio look like a minor league comparison.

Wouter

Call me "a lazy engineer", if nothing else, because I'm not reading through all that text (I prefer "efficient"...but whatever). You claim that you can create a tube of the same weight out of aluminum with the same bending characteristics as one from carbon. Well no $hit Sherlock! However, the diameters are not going to be the same.

Jake,

You don't hear me say this often, but :

If you are too $%#%@ lazy to even read the post then your comments are completely void of any meaning. They are are truly baseless.

And cut the BS about "efficiency". It took me 30 minutes to develop and implement the mathematical model producing the equivalency results. Even at a going rate of 100 buck per hour, this excersize would have been well worth the time of any professional engineer as the price difference between alu and carbon tubes is much bigger then that. THAT, my friend, is true "efficiency". And also what engineers are supposed to do, thats what they are trained for. To find solutions to design problems that satisfy the criteria and be as inexpensive as possible.

I don't know exactly how to intepretate this quote :



If you agree that this can be done, then you have just confirmed all my points.

If you disagree then, well, you have just proved to be one of those engineers that prefers gut feelings over true science. A dressed up monkey pretending to be an educated man. We already have far too many of those in our societies today. Please assure me that you are not one of those, I would consider that a loss.

I like you personally Jake, so take this post as a single issue disagreement, even though it is a very fundamental one.

I simply can't stand dumb people thinking that they have anything meaningful to say without having put in the effort to understand what is being discussed.

Wouter

Don't give Jake such a hard time Wouter, the problem with your spreadsheet is that you could calculate that a chocolate boom can be made as good as a carbon one, Yes it would have a large diameter and small wall, just like your aluminium one would.

When you go on to say "a wallthickness of 0.1 mm is impossible to achieve" I think that also makes your post pretty meaningless. (although I think you meant 1.0 mm)

In general terms most engineering materials except carbon have the same stiffness/weight ratio.

Carbon is the worst material for lazy engineers, because it is not homogeneous and can have different properties in different directions. It is a very hard material to design with. But can be amazing when used correctly.

As far as the efficiency of materials goes, you make a good point about efficiency of materials that are volume constrained, but most of the engineering on a cat is weight constrained. The only volume constrained case on a cat I can think of is where you are deigning for least drag, and then it is only really applicable with situations where the material is purely in tension. Like Dolphin striker support and stays.

Gareth

I have been following this thing for some time and watch how people think about things. I see for some reason that Wouter is anti carbon and he is an alu fetish, but i have to say that the boom he did designed will be working but you will never been hit by this shape because the damage would be severe.

Quote:
Carbon is the worst material for lazy engineers, because it is not homogeneous and can have different properties in different directions. It is a very hard material to design with. But can be amazing when used correctly.

I agree with this because it is the biggest problem with carbon, you don't have 1 type of carbon but several types and than not only the type of cloth or UD but also in flexibelity and than you have a lot of different types of resin where you can work with and i can a sure you that you don't have the time to follow the whole development in carbon and resins because it is going to fast.
The thing Wouter is right, is the money and carbon will be more expensive at this time than aluminium but i am also following the prices for the metal market (stainless,Alu)and i have to tell you that the prices for metals is going up more rapid than carbon.
The trick on this is that you try to get a design that is within the budget you have, or in alu,wood or carbon.

Regards,
Hans

What I meant to imply was that it didn't take me reading your entire post to realize that it's crap. You list materials that have a better tensile strength or lower density but not BOTH in the same material. You list some sort of table that's silly over complicated in that it ignores the diameter of the aluminum required to achieve the same bending properties as if it is not important. You're only presenting part of the picture because if you present the entire one, it weakens your argument. Again though, it's like arguing with a pig.

I think it's probably a decent idea for this boat to have a beam that starts with wood to be cost effective. But I was responding to your statement that carbon is for lazy engineers. Just go look at an F1 racer and tell my how "lazy" those engineers are.

Exactly !

So you need to look at each individual case in detail to determine what material to use. That is my main point. It is 180 % opposite of making everything from carbon laminate because it is so "good".

Also my alu boom doesn't have a LARGE diameter, it just has a LARGER diameter. There is a difference here. A chocolate boom would have a diameter nearing 1 mtr, that IS an impractical large diameter.

Clearly the larger diameter of alu is still so small that it is not an argument for not using it as a boom.





An alu wall thickness of 0.1 mm (0.0001 mtr) may be impossible to extrude but a wall of 1 mm (0.001 mtr) isn't. Therefor my alu boom example still stands as that one uses a 0.001 mtr = 1 mm wall.

This is high school stuff guys, please don't waste our time by making such rookie mistakes.






There are other materials like wood, plastics and even metals like copper that have noticeably different ratio's.




It is really not hard at all to design with carbon. Because it is so light, you can just pile up more and more matts on eachother (and under different directions) till the bloody things holds up under the loads. Without getting hit back by heavyness or a large volume. That is why it is so favoured by homebuilders. They hardly do any real designing.

It may be a hard material to design WELL with but apparently even aluminium is that for most engineers. This has nothing to do with the material but rather with "laziness"




That is not the full picture. If I'm volume constrained then I can still make an alu stiffness equivalent to carbon, I just can't make it the same overall weight. So we are back again at my initial statement. Carbon is preferable over alu when an engineer is limited BOTH in volume AND weight. If either one is not limited then it is not immediately clear which material is to be prefered. It will then dependent on other considerations like cost, availability, and stability of the component (wall thickness)





Correct. When it comes down to alu or carbon laminate the difference is volume are often so small that the increase in drag is negligiable. How much more drag will a 59 mm boom have over a 40 mm boom ?




Wrong again.

Situations with ONLY pure tension favour carbon a little more as here you can't play with factors like diameters to make both components the same in stiffness AND weight. This because both stiffness and weight are influenced to the same degree by a changing length measure. In bending, torsion or buckling this is not the case and here stiffness changes faster with varying length measures then weight. This disportionality is the reason why it is possible to design a tube with equal stiffness and weight when using different materials. Think about this.

The reason why carbon is not used in stays and dolphinstrikers is because it requires too much volume to get sufficient stiffness and strength and carbon is more sensitive to abuse and degradation and often this is compounded by being more expensive as well.

Stainless steel dolphinstrikers can be 3 mm thin (while being 25 to 40 mm wide). An equivalent carbon strap needs to be at least about 2.5 times as thick or 7.5 mm thick. It is alot easier to smash a 3 mm strap through a wave top then a 7.5 mm thick plate. Additionally when a stainless strap is hit very hard it will bend but maintain the beam in shape. Carbon will probably splinter or fracture and fail, bringing down the mast.

Stays is somewhat different. Stainless steel 1x19 cables have the same stiffness per area as carbon laminate. Dyform stainless steel cables have a better stiffness per area then carbon laminate. Again stainless will survive much more abuse then carbon which is important in stays. But most important of all, 1x19 steel cable costs 10 times as little as an equivalent carbon cable. Really the only downside to stainless steel cables are that they weight a little more. But if that is a problem then make your stays out of dyneema or similar fibres. Such fibres will shame both stainless and carbon but with the drawback of being much less abuse resistant then stainless. This last property is really holding back the use of fibres for stays.

Mind you the use of fibres of trap wires is an old trick by now. For nearly 10 years now a portion of the Dutch cat sailors are hanging of 3 mm dyneema or 2 mm D12 lines, with great succes. Much lighter then either stainless 2 mm 1x19 or carbon and significantly cheaper then both as well !

Currently there seems to be a drive to build cat hulls out of kevlar. It is lighter then carbon and it is also cheaper. The superior stiffness of carbon fibres is not really used in the hulls because the crossectional area of the hulls is already so large (think again about our alu/carbon example) that the minimal wallthickness needed allows other material to relatively easily arrive at sufficient overall stiffness. In the case of hulls this favours kevlar and seriously limits the drawbacks of using S-glass.

I guess my mainpoint I'm driving at is that cat sailors would be wise to understand these principles. It will allow them to not get scammed into paying alot of money for boats with fashionable materials that aren't really any better in what they are supposed to do.

Example : If you have the option to have your hulls build in S-glass, kevlar or carbon with the additional cost going up from glass to carbon then don't consider carbon, get Kevlar. You'll get the same quality in the hulls for less cost. If kevlar is not an option then seriously think about how much a little extra stiffness is worth in relation to paying significantly more.

Thanks for reading through my lengthy reply.

Wouter

It's getting way too heavy in here.
MMMMM, chocolate booms...delicious. They would be great for those long days of distance racing. Just take a bite off of the back end...

Jake,

I'm truly sorry to say this, but you are a dumb [censored].

All the things you state as counter arguments were adressed in my initial post.

But I guess you missed them because you were too lazy to actually read what I wrote.



Let me put it in a kindergarten format for you :

a 59x1 mm alu tube will have the same (bending, torsional, buckling) stiffness and weight as a 40x2 mm carbon tube.

Wouter

Hello Hans,




My boat has :

ply hulls
epoxy resin and glass tape as joints, with some carbon and kevlar local reinforcements
aluminium mast and beams
carbon laminate rudder boards and stocks
Glass vinylester daggerboards
stainless steel dolphinstriker, stays and mast/beam fittings
dyneema trapeze wires.


I can be accused of many things, but not of anti-carbon or alu-fetish tendencies.

It is as I always said. Look at the individual design problems in detail and choose the best material for that application.

Sometimes this is carbon, other times this is aluminium at other times it is something else.




Agreed, this was a quick knock-up of a design. I have an idea of how to make one that is less hurtful when hit. It is a little more complicated and I didn't have time to work that one out fully, including drawings etc.

I'm probably going to propose that design to Gato for his mini650. Roughly speaking it is a round section made from straight planks that has been routed and sanded to have round sides. the flat top and bottom planes will take the carbon cloth or aluminium strips to get it up to sufficient strength and stiffness. This building method, but without the carbon or alu, is indeed used to produce lightweight timber round spars for masts and booms on traditional Dutch sailing boats.

Wait a minute; I have a document somewhere I written in 1999 or so ...

Wouter

Lightweight timber spars as used today for traditional Dutch sailing boats.

Gato are you reading this ? This is a good option for your mini650.

This building method allows you to build hollow tubes of plain timber plancks. It even allows you to make tapered hollow sections. Some builder decide to coat the outside with a layer of glass to increase the stiffness even more.

I think the drawings are selfexplanatory.











My idea is to keep the top and bottom parts flat (only route the little points off) and use the flat surfaces to glue or screw carbon cloth or alu strips too.

The timber properties should be be enough to withstand the loads in the sideways direction.

If you don't to spend much time rounding the sides then you can just route the sharp points of and keep a multi chined pentagonal outer shape. That won't hurt to much at all when hit by your head.

Also if you don't really want a perfectly round section then a good simplifications would be to not to use 8 elements but only 6. Two larger ones on top and 4 on the sides. You would then only have to round the sides a little and leave the rest as it is.

I suspect that this 6 element hollow spar (possibly tapered) could well be just as strong, stiff and light as the earlier (simple) design. It can be homemade realitively easily and cheaply. Ofc ours different cross section profiles can be made by varying the angle under which the elements are glued together.

As I said earlier this setup is used as masts and booms on (small to large) traditional Dutch sailing boats. These spars can take a good loading before failing. And they are surprisingly light.

Wouter

Wow ... this is impressive. I'm a dumb [censored] and need stuff in kindergarten terms for me. Can I note for the record that the diameter of the aluminum tube is NOT the same diameter as the carbon tube? Why exactly have you resorted to calling me names and insulting me?

As is so often the case you should take Wouters engineering based arguments with a degree of scepticism.

Gareth

Wow way out of hand. Wouter there was no need for name calling. You are reminding me of a certain individual called Sam, remember him?