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Sakari Aaltonen
12-09-2004, 06:19 AM
Carbon fiber reputedly is cheaper than it used to be. Tubes made for industrial use could conceivably be pressed into service as strong and light spars. (Some people apparently make CF spars themselves. But I'm not clever enough for that.)

But what about scantlings? Like, I have a 4.5m (15') mast, 75mm (3") thick at the most. What should the diameter and wall thickness
be with CF?

Dave Gerr's Elements of Boat Strength seems to have practically nothing on this. Is there another source?

Thank you,
Sakari Aaltonen

Pete Dorr
12-09-2004, 08:38 AM
Sakari

Check out http://www.fibersparsports.com/ or any other vendor of windsurfing masts. I bet you could use one of these - probably need some reinforcement where you attach your halyard blocks.

400cm, 430cm, 460cm are all standard lengths

The carbon content varies based on how it will be used. If I were going to use one in a sailboat I'd stick with a wave mast as its beefier.

Pete

mmd
12-09-2004, 08:48 AM
Two problems arise; one is how to calculate the scantlings, the other is recognizing the limitations, as well as the strengths, of the material.

The first problem can be overcome by straightforward engineering. A mast is merely a column, sometimes guyed, sometimes free-standing. An introductory book on strength of materials such as Schaum's will give you the formulae to calculate column strength. Then a second problem arises - what are the loads placed on the column? Ah, now it gets a bit sticky. The loads on a mast are all over the place - side loads, torque loads, compression loads, etc., etc. How to resolve all these into a coherent (and simple) equation? After all, it's just a little boat mast, right?

Skene's 'Elements of Yacht Design' gives formulae to calculate the loads on a mast based on the righting moment of the hull. These are pretty good, and I would reccommend the book to you. The problem that arises is how do you determine the righting moment of your hull? Well, that's another subject altogether. Marchaj gives even more precise formulae (read, complicated) in his book 'Aero-hydrodynamics of Sailing' based on righting moment, wind pressure gradient, etc., but this is a bit weighty in both theory and cost for your small boat.

Maybe the best way is to reverse-engineer it from the stick that works. Using your newfound engineering skills a la Schaums, calculate the section modulus of the present mast. From sources such as The Encyclopedia of Wood, determine what the ultimate tensile strength (UTS) of the wood fibre parallel to the grain is for the species of wood that your present mast is made of. Calculate what the bending moment is to achieve the stress in the mast that reaches the ultimate tensile strength of the wood. Calculate what loading, evenly distributed from clew to peak, produces the bending moment found from the above. Divide this figure by the safety factor commonly used for masts (say, 5). Now you have a load that you can apply to the engineering of your new carbon fibre mast.

Knowing the load and tensile strength of the CF (remember to allow for fibre orientation!), calculate the required section modulus that will support the load, making sure to apply the safety factor. Determine the appropriate cylinder diameter and wall thickness required to achieve the calculated section modulus. Make sure that the material can withstand the load by calculating the tension and compression loads on the extreme fibres of the mast and comparing the results to published data on the material. If the stress is less than the UTS and ultimate compressive stress (UCS) of the material, your mast is strong enough.

The second problem is a bit more esoteric. Carbon fiber has a much higher modulus of elasticity than fibreglass. This means that it will bend less than 'glass for a given load (good) but because it isn't absorbing the loads implied by bending, that energy is being transferred to compressive and tensile loads, which skyrocket. This makes the material brittle and prone to catastrophic failure, especially if the continuity of the fibres is broken. Therefore, scrapes, nicks, drilled holes, etc. are to be avoided.

Or, you could just buy a CF tube sized by rule of thumb and try it. If it works, who cares if it might be heavier than necessary? If it breaks, buy a bigger one next time. ;) :D

George Roberts
12-09-2004, 10:46 AM
Sakari Aaltonen ---

mmd is correct. The engineering is straightforward but long.

Just buy TWO (2) sized by thumb. Carry one as a spare until you decide that what you have is sufficient.

Sakari Aaltonen
12-09-2004, 11:03 AM
Originally posted by George Roberts:
Just buy TWO (2) sized by thumb. Carry one as a spare until you decide that what you have is sufficient.CF may be cheaper than it used to be, but I still don't think it is cheap. It just possibly is not as outrageously expensive as it was, say 10 years ago. Buying TWO of everything is still too expensive.

So, no CF scantlings available? Could aluminium scantlings be pressed into service, modified in some way? Aluminium (tube) spars have a tradition, haven't they?

Sakari Aaltonen

MJC
12-09-2004, 11:08 AM
Sakari:

Carbon fiber or CF/Kevlar is available in a form called a "sleeve" - preknit and flexible. Not very expensive. I think it makes mast construction a possible DYI project. Think along the lines of several layers of sleeves laminated over a very thin walled plastic tube (a friend is saving me the 4 foot long plastic tubes that plotter paper comes on).

Link to Soller Composites - the folks I'll be ordering from. (http://www.sollerpaddles.com/composites/carbon%20fiber%20sleeves.html)

I'm going to try a carbon fiber/kevlar sleeve over a thin walled piece of bamboo inner shell this coming spring. My project is smaller than yours though. Bamboo might be hard to come by for you, assuming you're Finnish. I just cut it down on my trips to Tennessee or North Carolina - where it grows wild.

mmd
12-09-2004, 11:10 AM
To my knowledge, there are no compiled scantlings tables nor standard formulae for selecting CF masts. Using formulae derived for one material to size a component of another material is not reccommended. There are no short-cuts in engineering. Sorry.

Ed Burnett
12-09-2004, 11:25 AM
Well, mmd is correctish, but misses out something rather important.

In general with hollow tubes, the best bending resistance comes from a combination of large diameter and thin wall. This is all pretty intuitive stuff. With timber spars, one is limited in how far you can go down this road by the need to preserve the section stability of the spar. A paper thin walled tube will flatten and collapse rather easily, which will somewhat decrease its usefullness as a spar.

As a rule of thumb for timber spars, a wall thickness of 20% of diameter has been found to be reliable, although you can get away with less.

Now, when one starts to look at Carbon Fibre, you are obviously going to have nothing like that much wall thickness. In practice, what you have to do is engineer the laminate in the spar not only to provide overall bending strength (from fibres running up and down the spar), but hoop strength in the section to keep it stable.

This is done by adding fibres that wrap around the spar, both inside and outside the main body of UD fibres that run up and down. The fact that this 90 degree material is added either side of a thick wad of UD going the other way creates a sandwich structure to give the section the required hoop strength. To cap it all, one would also add fibres that spiral round at +/- 45 degrees to deal with torsion.

So, yes, you can reverse engineer the bending strength of the spar (this is a perfect approach when one has evolved a wooden spar that is the right strength), however you then have to consider the other aspects of carbon spar design to create a laminate that is appropriate.

Custom carbon spar building requires tooling and is probably more than you want to get into. I would have thought your best bet would be to forget the sums and go shopping for a Carbon tube that feels like it has about the same stiffness as your current mast. You could compare the candidates to your current mast by supporting them on a trestle at each end, and measuring the deflection when you hang a certain weight in the middle. Then make a note on the weight saving you can achieve and decide if it is worth the money.

mmd
12-09-2004, 01:11 PM
Thank you, Ed, for pointing out my omission. I was trying to illustrate how complicated it can get when trying to calculate mast scantlings without getting too long-winded, and I neglected to mention all aspects of the challenge.

It is always nice to hear many knowlegeable voices discoursing on a given subject.

Bayport_Bob
12-09-2004, 03:03 PM
These guys sell CF mast kits for their sailboats. I'm sure they can come up with the necessary design for your rig...

BoatBuilderCe ntral CF Mast Kits (http://www.boatbuildercentral.com/products.php?id=36&Carbon%20Fiber%20Mast%20and%20Push%20Pole%20Kits)

- Bob

Sakari Aaltonen
12-10-2004, 03:11 AM
Originally posted by Bayport_Bob:

BoatBuilderCe ntral CF Mast Kits (http://www.boatbuildercentral.com/products.php?id=36&Carbon%20Fiber%20Mast%20and%20Push%20Pole%20Kits)
Thanks, but when I figure in taxes and shipping, such a kit will cost about USD300. That's seriously expensive for a smallish mast, and the kit also looks like a mess to assemble.

I still can't help thinking an industrial, off-the-shelf, general-purpose, CF tube might be affordable.

bainbridgeisland
12-11-2004, 12:58 PM
Originally posted by George Roberts:
Sakari Aaltonen ---

mmd is correct. The engineering is straightforward but long.
Having taught a dozen Engineers how to do it, I do not think engineering of anisotropic composites is straightforward. These were experienced, smart guys, but most of them needed to review their matrix algebra before they could begin to follow the micromechanics of a laminate. Also, Material and Process Engineering must come into play since slight variation leads to major changes in properties.

Anisotropic means the material properties are different as direction changes. Some materials, like wood, are anisotropic but long established methods allow engineers to easily analyze the material.

Carbon fiber does not fall into that category. For example, off axis strength and stiffness of a single strand of carbon fiber is far less than the on axis direction. Since the fiber is extremely rigid and off axis loads are carried by the resin (at a micromechanical level), this means a carbon fiber laminate is very sensitive to off axis loads. So stress concentrations cause off axis loads producing a potential failure. (See MMD comments about other off axis loads too.) Even the best micromechanics programs followed by the finest finite element analyses method have a hard time predicting performance at this level.

If it is so hard, why do carbon fiber masts work? They are generally engineered (and not all engineers can do it). They are over designed. Attention is paid to details so that stress concentration features are resolved. Fabrication and quality control are well done. Riggers are coming to understand the limitations of the material when attaching hardware.

Venchka
12-11-2004, 02:22 PM
Originally posted by Sakari Aaltonen:
...

But what about scantlings? Like, I have a 4.5m (15') mast, 75mm (3") thick at the most. What should the diameter and wall thickness
be with CF?

Thank you,
Sakari AaltonenSakari,

Aren't you building Oughtred's GANNET? Like this...

http://www.duckflatwoodenboats.com/designers/oughtred/gannet2.jpg

With a sliding gunter or possibly a marconi main? A jib stay, shrouds, gooseneck, yard (with the gunter rig), etc.? Since wood has worked so well for this type of application and is relatively cheap, why re-invent the wheel? Make your spars hollow. Compared to the traditional way, that is very high-tech. I for one would be interested in hearing an expert opinion on how a carbon fiber tube would handle all of the loadings imposed by the various bits of standing rigging and spar hardware. A carbon fiber mast on a windsurfer is doing vastly different things than the same tube on a boat like Gannet.

Wayne
In the Swamp. :D

Dan McCosh
12-11-2004, 02:43 PM
Any notion as to where these industrial tubes are sold, and for what price? I'd be interested in such a material for a spinnaker pole.

George Roberts
12-11-2004, 04:43 PM
bainbridgeisland ---

Tensor math, indicial notation, perhaps more modern methods and teaching composite engineering is almost trivial. But ...

You can look up the answers (which is what are needed) in many texts and on many websites.

I even have written a booklet on composite issues. (Not masts no current need for me to)

My booklet my engineering scantlings:

* Design rules for wood core / cloth epoxy face construction valid
** for displacements from 100 pounds to 600 pounds,
** for when you can overpower the wind and water and for when you cannot,
** for E-glass, S-glass, carbon, and Kevlar 49 fibers in plain and satin cloth, and
* Engineering analysis.
* Strength Optimals.
* No building techniques.

The actual scantlings are only 2 equations

*nominal weight of cloth for each face: 17 (S/3)^(1/3) Fiber_type_factor
*Softwood thickness for the core: .120 (S/3)^(1/3)

2 similar equations are needed for masts.

bainbridgeisland
12-11-2004, 08:05 PM
OK George, I hesitate to get into this but...

To reduce scantlings to two equations, you must make many assumptions that may or may not be true.

For example, are you using style 7500 glass fabric, style 7781 or something else? Since the strength of style 7500 is 2/3 the strength of 7781 per square inch obviously they cannot perform in an identical way.

Another example, many reinforcements have different stiffness and strength in the warp direction compared to the fill direction. So obviously they do not perform identically unless direction is specified.

Another example, the stiffness of glass reinforcement varies as the angle changes. Thus, reinforcement placed at 10 degrees is not the same strength or stiffness as reinforcement placed at zero degrees.

Another example, the final mechanical properties, in a given direction, of a laminate approximately follows the rule of mixtures. Example for modulus: Ec = Ef*Vf + Em*Vm Thus altering the fiber/resin ratio alters the stiffness. Altering the modulus of the resin (i.e. the manufacturer and or cure schedule) alters the stiffness. There ar other factors too, like hygrothermal condition, built up stress during cure and so on.

Besides all this, designing glass is much easier than designing for carbon fiber. This is because glass is isotropic within itself and can take off axis loads much better. Therefore, if your axis of load (or reinforcement) is off a little bit, the glass product will behave as predicted. A carbon fiber product subject to this off axis condition will not behave as predicted. This is because the carbon fiber itself cannot handle the shear loads induced by the off axis primary load.

Don't know if you guys remember all the carbon fiber rudder shafts that broke in the Fastnet Race. This off axis loading problem is the primary reason most of those shafts broke.

I reiterate, designing carbon fiber composites is not trivial. You cannot look it up in a standard engineering textbook unless it is 'Composite Design' by Tsai or some other specialty text and a text like this alone is not enough because the you must also handle the Materials and Process part of the problem. Many assumptions made in everyday engineering cannot be successfully employed when designing carbon fiber products. So be careful.

Venchka
12-11-2004, 11:12 PM
All of the above reaffirms my lay suspects that buying a generic carbon pole ain't gonna work with a gooseneck, gunter saddle, shrouds and jib stay pulling, pushing, twisting and bending in all sorts of unknown ways. Hollow spruce or doug-fir work. They look right on a wooden boat too.

If it ain't broke, don't fix it. Wayne
In the Swamp. :D

Hwyl
12-12-2004, 03:02 AM
There is a section on spar building here http://www.sailingsource.com/cherub/masts.htm . It's high on the practical issues.

I went to a seminar by Hall Spars more than ten years ago. They were excited by the possibility of carbon spars. One of the interesting things that they did was too replicate as close as possible the characteristics and external dimensions of an aluminium spar on an iceboat (one of the guys was an avid iceboat racer, so they could get good numbers). The weight was the same, the centre of gravity was the same, the deflection was the same. The ice boat sailed consitently better with the carbon spar. They had not figured out why, but postulated that it was because of "speed of coming back from deflection".

They also said that a good portion of their market (at that time) was from people who wanted lighter masts, just for the ease of tansportation and rigging. I think there was one customer with a catboat, and the weight was the difference between being able to erect the stick on his own or using a crane.

So I'll disagree with Wayne, and say, definitely go with carbon.

Sakari Aaltonen
12-12-2004, 04:40 AM
Originally posted by Venchka:
Sakari,

Aren't you building Oughtred's GANNET?

With a sliding gunter or possibly a marconi main? A jib stay, shrouds, gooseneck, yard (with the gunter rig), etc.? Since wood has worked so well for this type of application and is relatively cheap, why re-invent the wheel? Make your spars hollow.I launched the Gannet several months ago (with hollow wooden spars); I just used its mast as an example, here. The CF spars would be used on another boat.

Sakari Aaltonen

George Roberts
12-12-2004, 12:01 PM
bainbridgeisland ---

I also hesitate to get into this so I will only say with regard to scantlings ...

It is not necessary to handle all possible materials or all possible construction processes. It is only necessary to prescribe materials and construction in sufficient detail that the finished product has properties within the range that the engineering is based on.

Along the lines of an issue you have raised ...

It would be foolish to base scantlings on the assumption that the fibers are aligned with the forces and not make that alignment a requirement of the scantlings.

Venchka
12-12-2004, 09:33 PM
Hwyl,

There is no doubt that folks who make spars for a living can design, engineer and build carbon fiber spars for a specific application.

The question here is can the carbon fiber tube equivalent of a Home Depot 1-1/4" dia. closet rod work as a mast on a sailboat? Look at the original post.
Tubes made for industrial use could conceivably be pressed into service as strong and light spars. In that context, I doubt that any spar maker worth his resin would agree. For that matter the size, length, sail area, rigging, hull shape, displacement, etc. of the mast weren't stated.

The industrial tube pressed into servive as a spar might work famously until the first gust over 15 knots made it snap like a twig.

Carbon fiber spars appear to be an art and science unto themselves. Generic carbon fiber tubes would be suspect at best. Dangerous at worst. The shards from broken carbon fiber are lethal. Ask the F-1 drivers who have puntured their tires on carbon fiber shards with disasterous results.

Wayne
In the Swamp. :D

[ 12-12-2004, 09:34 PM: Message edited by: Venchka ]

Sakari Aaltonen
12-13-2004, 02:11 AM
Originally posted by Venchka:
The industrial tube pressed into servive as a spar might work famously until the first gust over 15 knots made it snap like a twig.

Carbon fiber spars appear to be an art and science unto themselves. Generic carbon fiber tubes would be suspect at best. Dangerous at worst. The shards from broken carbon fiber are lethal. Ask the F-1 drivers who have puntured their tires on carbon fiber shards with disasterous results.This is being terribly negative. Industrial CF tubes are hardly likely to be as weak and brittle as that - they are meant to compete with steel and aluminium, not cardboard.

And if CF shards can be lethal, then so can wood splinters.

Sakari Aaltonen

Ed Burnett
12-13-2004, 05:48 AM
I am glad to see some of the more complex elements of Carbon spars now being considered. That said, once one is aware of the possible difficulties, it is possible to go ahead in a conservative but simple manner. Like lots of things in yacht design, figuring out the answer to a specific question is just a matter of getting on and doing it - the tricky bit is knowing what the questions are in the first place.

At the end of the day, we are dealing with a small boat here. A huge amount of design effort and expertise (ie. time and money) is not warranted if only because that takes a lot of time which could be spent sailing (which presumably is the eventual aim). On the whole, I wonder if a Carbon spar is even going to make a noticable difference to this boat. The only time you would feel a difference is when you step or unstep the mast, the rest of the time I doubt you could detect any change in sailing characteristics. So, if you plan on whipping the mast in and out on a regular basis (as may well be the case), then it could be worth a look.

I think the fears of using an industrial tube are not that valid. Providing the tube would be used as a load bearing strut of some sort in it's industrial application, I don't see any problems in using it as the basis for a simple mast, in a small boat. Sure, there are potential tricky bits at the ends and attachement points, but nothing that can't be dealt with. One is making the assumption here that the industrial CF tube will have been designed to take into account the various intricacies discussed above.

As I said in my earlier post, I see no real problems providing the tube exhibits similar overall stiffness to the current mast. Again, I would stress that this is not a solution that can be applied to all things. Bigger boats and bigger rigs do need more thought.

MJC
12-13-2004, 08:17 AM
Dan:

There's a carbon fiber spar co. in Chesterfield Twp., they do CF spinnaker poles (but maybe for bigger boats than yours?).

Offshore Spars (http://www.offshorespars.com/index.cfm)

Dan McCosh
12-13-2004, 11:06 AM
The spinnaker pole is 16 ft. x 4 ins.. I've looked into standard CF tubing from sparmakers, and it ends up about \$1,200, which isn't worth it for the results. The idea of making the pole easier to handle is the maint attraction, although it isn't all that bad now. I'll also stick to my composite resin/ cellulouse micro tube mast.

Venchka
12-15-2004, 01:59 PM
Here you go. Roll your own carbon fiber and fiberglass spar.

Carbon Spar Making (http://www.lmorocz.com/BoatBuilding/mast01.htm)

Wayne
In the Swamp. :D

Terry Etapa
12-15-2004, 02:54 PM
Originally posted by Ed Burnett:
Sure, there are potential tricky bits at the ends and attachement points, but nothing that can't be dealt with.From my experience, the tricky bits Ed mentions are not trivial. I've worked carbon fiber composite structure on the F-22, Airborne Laser, and 7E7. Sizing the "acreage" away from connections is often straight forward. Most often, when ever you put in a fastener, you will need to ramp up your plys. The composite fails in bearing/bypass. The allowables for this type of failure are based on your lamina, laminate layup, and environment.

The vendors may not have the material allowables you need to size the "tricky bits". While working for a small firm doing composite pole models for unmaned aerial vehicle electronics testing, we had to get our materials tested. The vendor gave us no data beyond the lamina.

12-15-2004, 02:58 PM
Here's another outfit making carbon fiber spars:

http://www.forterts.com/pro.html#Sailing

They advertise in Messing About in Boats, and make the spars that are offered as an option on the Arey's Pond (fiberglass) catboats.

They can probably advise as to appropriate specs for a particular use.

George Roberts
12-15-2004, 06:56 PM
There are two types of commercially available CF tubes.

The first type is a pulltrusion. The fibers are aligned with the length of the tube.

The second type is a filament winding (or layers of woven tubing). The fibers are aligned 45 degrees more or less to the length of the tube.

Both have a uniform interior diameters so blocking could be inserted where bits and pieces apply a concentrated load. I expect one could make an off the shelf tube work, but ...

I expect that any off the shelf item would be too expensive compared to alternatives.

bainbridgeisland
12-15-2004, 08:23 PM
There are some simple ways of making an off-the -shelf carbon fiber spar.

Simple 1: Buy 2 or more identical sailboard masts. After surface prep epoxy glue one inside the other. For stronger and stiffer masts glue a third one inside the other two.

Simple 3: Want a longer mast? Insert above examples into standard CF tube of the correct scantling. You will need extra reinforcement to resolve non-linear loads for this one. But it can work.

Sailtrack needed? Sikaflex plastic sail track in place (Holt Allen or Ronstan, I can't remember). Add a little glass around the spar at the ends of the track so it can't peel off.

Remember, do not bolt things to carbon fiber tubes unless you know what you are doing. Use adhesives and sleeves to connect, much safer.

Edit to correct spelling

[ 12-15-2004, 09:24 PM: Message edited by: bainbridgeisland ]

Venchka
12-15-2004, 11:14 PM
At \$350 USD and up each, glueing up 2 or 3 Windsurfer masts gets a little pricey, eh? :eek:

Carbon fiber tube prices may have come down. From stratospheric to just plain rediculously expensive. For small boats, wood still wins. Sitka spruce looks affordable compared to carbon fiber.

Wayne
In the Swamp. :D

bainbridgeisland
12-16-2004, 06:25 PM
I agree, wood still wins. A well designed and built wooden spar is as light and stiff as Aluminum. Carbon fiber spars are only needed for very high performance boats. There are only a few timber boat designs that can begin to justify the expense.

Ed Burnett
12-17-2004, 04:33 AM
Terry,

You are of course right. The tricky bits are not trivial. The assumption that underlines my comment (that I guess I should have stated better), is that we are are dealing with a simple rig here.

Many simple and small boat rigs can be set up with few or no fittings away from the ends of the spar. Very traditional rigging techniques can work very well with carbon spars - soft eyes on bolsters for lower shrouds for example. A wooden plug in the upper end of the spar can be fitted to leave a shoulder for a mast band at the top of the spar to sit on. In other words, it is possible to fit out the spar with no significant fastenings in the carbon tube.

The reason I am posting on this thread is that I think it is a shame to discourage a spirit of experimentation. I am not saying that anyone can go and buy a great big Carbon drain pipe and use it as a mast for a large offshore boat. But, with a bit of common sense and an awareness of the possible pit falls, I see no reason why someone can't try it on a small boat.

Along with some of the other posters, and as I have mentioned above, I don't actually think a carbon mast will make any difference to sailing this boat. What it might be is easier to step and unstep and that is worth a bit of trouble in some cases.

Redeye
02-17-2014, 05:10 PM

I've been quoted 12-15K for a simple 16m carbon mast for a 40ft lightweight boat. And comparable to alloy.

That's pretty sharp. Price climbs to about 20K for more fancy tapered mast.

Of course, where I am I will pay abotu 8-9k for perfect old growth douglas to make the same mast in birdsmouth. And it'll be 160kg, vs 60kg.

Michael Wick
02-18-2014, 09:03 AM
I've built five spars and broken two using Soller carbon and kevlar socks. I've used various mandrels and carbon skin. The price is small, and it's fun.

capefox
02-18-2014, 12:28 PM
Some of the most cost-effective composite materials -- made of cellulose fiber and lignin -- have leaves on them.

Paul G.
02-18-2014, 02:42 PM

I've been quoted 12-15K for a simple 16m carbon mast for a 40ft lightweight boat. And comparable to alloy.

That's pretty sharp. Price climbs to about 20K for more fancy tapered mast.

Of course, where I am I will pay abotu 8-9k for perfect old growth douglas to make the same mast in birdsmouth. And it'll be 160kg, vs 60kg.