Epoxy/glass mast for a cruising yacht?

[Inquisitor]

First blush...

All this is great information. To make those kind of statements, sounds like she may have far more experience with room-temperature, hand-lay-up than I. We definitely want to access that.

Referencing the first-cut design [90/45/0/0/0/-45/0]s (Message #4).

Her #1 - Off the top of my head, I believe she is correct. However, there are some considerations for such a high percentage of zeros to consider. I want to run some numbers. I’ll follow this one up later.

Her #2 - I am curious of her rational for having the +/- 45 degree plies on the inner and outer surfaces. I have two reasons for preferring the 90s on the inner and outer. (1) By having 45 on the outer, it would follow that 0s would be next to 90s. This results in higher interlaminar shear stresses (see msg #14). (2) Beams in bending do have some shear forces and thus the +/- 45 degree plies are more important than the 90s. Thus, the 90 on the outer surface gives you just that much more protection of what’s semi-important (45) and which both protect what’s really important (0s).

Her#3 – THIS IS A GOLD-MIND! I had no feeling of what safety factor to use for room temperature, hand-lay-up. Robjl – Do you have any idea what safety factor is used in your aluminum mast design? Say if it is 4, you could simply take this 5.5/4 = 1.375. In the spreadsheet, you would need to fiddle with the thick_g until all the margins at the bottom are at least 1.375!

Her#4 – 0 degree plies need to be the unidirectional fabric. 45 can be the regular cloth, but they are of less strength and stiffness and would have to be accounted for. 90… doesn’t really matter one way or another.

P.S. - Is she married?

 

[stewi]

For the unidirectional (0) fibers, I was considering single fiber strands and not wooven. Use wooden blocks on both ends of the mast, packed with nails. Tie the strand around one nail and go all the way to the other end and loop the fiber around another nail while keeping on tension on the fiber. Use a spring gauge to get a uniform load on each fiber.

 

[Inquisitor]

I’ll kneel before the high priestess...

Her #1 - The numbers I ran were so negligible, I was hoping that you all would forget I brought it up, but my conscience got the better of me. I need to acknowledge her experience! 70% works great.


Since the zero degree thickness is projected to be 0.064”, that would mean we need a total laminate thickness of 0.064/70% = 0.091”. So if we use regular weave cloth for the off-axis plies, and use a stacking sequence…

[0c/45c/0u/45c/0c]T (Where subscripts c=cloth, u=unidirectional)

… would indicate that the cloth needs to be 0.091*30%/4 = 0.0069” (0.174 mm).

We will need to revise this number once we get a real-world safety factor for an aluminum mast.

Does anyone have any as-laminated thickness numbers for various glass cloth weights?

 

[Inquisitor]

Liability...

All off the record of course as no-one wants to take possible liability.. we all understand that.

I mean, McDonnell's getting sued and losing because their coffee was too hot!
Give me a break! One of the few aspects of the US, I dislike... too many lawyers with too much time on their hands!

I hate lawyers!

Now, if I'm going to be sued because a mast breaks... I need to bail out now! There are too many unknowns, S.F., fabrication variations that I don't have a handle on. Robjl's and probably most of your alls glass work will certainly put mine to shame, but I'm still going to try it out for my boat(s).

 

[Inquisitor]

Robjl,

I've searched this site for material properties… nominal thicknesses, stiffness and strength properties. Marine construction seems to follow the same trend that the aerospace field does. It takes a lot of money to do testing and they keep those results close to the vest... both for cost and the liability reasons. I had hoped that there would be more openness here since people have been willing to offer advice on other technical issues that could have just as many liability concerns. You may be running into the same problem with your search for properties. As I might have mentioned somewhere along the way, the properties I’ve been using so far are based on 78% fiber volume… definite… verified… A-basis numbers! What I did find on this site (frankly) scares the **** out of me!

In the topic “Resin infusion and resin content”, Eric Sponberg sounds quite knowledgeable and says some things in #2 and corrects himself in #6, yet appears to make the same slip of the tongue… or maybe its not a slip and its really that bad! In #10 he states the general philosophy of keeping these properties close to the vest.

I knew we were not going to get 78%; but, I did expect that we could get at least 60% fiber volume. Anyway, he’s saying 30% fiber volume! If that is the best we can achieve with hand-lay-up, we cannot build a mast with glass, carbon or anything else. Fibers in 70% resin will have squat for compressive properties! And anything near comparable to an aluminum mast is a pipe dream.

I’ll send something to Eric and maybe he can point us somewhere.

 

[Robjl]

Thanks Inq, I'm still wating for specs, but I did find a few sites that are interesting.
www.sailingsource.com/cherub/masts.html
www.compotech.com
www.allyachtspars.com.au
www.jutson.com/articles/dec96/html
www.seldenmast.com
None are on our topic but they each have bits that add to a picture. The Selden site has some nice gear that may give you a picture of cruising rigs.
I like ES but I think he has an aversion to anything with wires holding it up.
I like your terminology though. "Pipe" dream indeed.

 

[water addict]

Robjl,

I've searched this site for material properties… nominal thicknesses, stiffness and strength properties. Marine construction seems to follow the same trend that the aerospace field does. It takes a lot of money to do testing and they keep those results close to the vest... both for cost and the liability reasons. I had hoped that there would be more openness here since people have been willing to offer advice on other technical issues that could have just as many liability concerns. You may be running into the same problem with your search for properties. As I might have mentioned somewhere along the way, the properties I’ve been using so far are based on 78% fiber volume… definite… verified… A-basis numbers! What I did find on this site (frankly) scares the **** out of me!

In the topic “Resin infusion and resin content”, Eric Sponberg sounds quite knowledgeable and says some things in #2 and corrects himself in #6, yet appears to make the same slip of the tongue… or maybe its not a slip and its really that bad! In #10 he states the general philosophy of keeping these properties close to the vest.

I knew we were not going to get 78%; but, I did expect that we could get at least 60% fiber volume. Anyway, he’s saying 30% fiber volume! If that is the best we can achieve with hand-lay-up, we cannot build a mast with glass, carbon or anything else. Fibers in 70% resin will have squat for compressive properties! And anything near comparable to an aluminum mast is a pipe dream.

I’ll send something to Eric and maybe he can point us somewhere.

Ah yes- now you are working with realistic numbers finally. You might get 50-60% fibers in the very highest quality construction, but then you gotta be damn sure you have good resin infusion through the part or you aint got sugar. Even in some of the highest quality composite construction in the marine industry, mechanical propoerties can be 50% or more below theoretical. Thats why safety factors are usually double for composite parts. So now take your safety factors in your design spreadsheet and double them- then compare that to the Aluminum spar design with metal safety factors. That is how your design comparison should be done.

 

[Eric Sponberg]

My presence has been requested.

I have read through the entire thread, skimming at spots, and I have not studied Inquisitor's spreadsheet, so I cannot comment on its specifics. Let's presume that it is correct in it science and math. I also took a look back at that thread on resin content of two and a half years ago just to make sure what I said! And yes, I do prefer masts without wires holding them up, but have designed my share of stayed aluminum masts too.

Here is some perspective from my point of view:

I would never design an all-fiberglass mast. Been there, done that, had some some not too nice experiences. This all boils down to what are respectable properties to expect in the finished laminate, particularly with common boatbuilding practices, which do include wet lay-up, prepreg lay-up, and vacuum bag cure at room temperature, at least for the do-it-yourselfer. If you go to a production facility, there are autoclaves available for higher quality composites, but you have to pay for the service.

I have found that fiberglass, compared to aluminum, may be stronger, but it is never going to be stiffer. Yes, you can compensate for the lack of material stiffness by increasing the section size so that the ExI stiffness is the same for the two materials. But the guiding light behind mast design for a stayed rig is to make the mast as small as possible because it is such a large producer of drag. Therefore, a smaller mast section is better, and fiberglass takes us in the wrong direction compared to aluminum. Aluminum has a modulus of elasticity of 10 MSI, whereas well-built fiberglass has a modulus of no better than 2 MSI, in my experience. Inquisitor's modulus numbers from the aerospace industry, while probably correct (he has much more experience there than I do) are simply not easily achievable at reasonable cost in boatbuilding.

If you elect to go composite and accept all that that entails regarding the process, carbon fiber wins hands down over fiberglass. It is easy to lay up, and its overall strength and stiffness properties are better. In common boatbuilding practice, it is possible to achieve a laminate strength between 60 KSI to 100 KSI, and a modulus of between 7 MSI to 10 MSI. The variation here depends on the quality of the process and the people doing the work. Therefore, carbon fiber reaches the material properties of aluminum, and it is lighter than aluminum, so you can go with the same mast section dimensions at lighter weight.

The fear of carbon fiber mast "exploding" as I have seen in other threads, is really indicative of the fact that those are racing masts built to very high specifications with very low factors of safety. Really good quality carbon laminates do shatter, and in a racing boat they are more likely to shatter because of the low safety factors, which usually border on the level of 1.1 to 2.

In a cruising boat, I would typically design a mast to a factor of safety of 3, based upon a load related to the maximum righting moment of the boat. Some owners may ask for a higher factor of safety, like 4, and really conservative people might request 5. But If you can't reliably design and build a mast to that level, then you don't know what you are doing and should give up. FS = 3 is plenty, and these masts last for years and years.

Getting back to stiffness, all masts, whether stayed or free-standing, are stiffness critical. So modulus of elasticity and moment of inertia are really important. Taken to the extreme, one could go to a very large section and a really thin wall thickness to get the properties that you need. But you run the risk of premature wall buckling. In my work, I have found that if your wall thickness in a composite mast gets below 3% of the diameter (minor diameter in a non-round section) then you run the risk of premature buckling. This rule, then, serves as a limit on how big you can design your mast section.

As for lay-up, any mast is going to need a certain percentage of 0-deg fiber and off-axis fiber (+/-45 and 90 deg). I have found that in a stayed rig, or in a round-section free-standing rig, the percentage of 0-deg fiber to off-axis fiber would ideally be about 80/20. As the mast section gets more non-round, as in wingmasts, then this ratio drops to 60/40. The extreme outside and inside layers should always be +/-45 because they sandwich the 0-deg fibers to keep them in column. A 90-deg layer on either the inside or outside surface will be prone to cracking that can propagate through the entire laminate. The 90-deg fibers should be equal in quantity to the +/-45-deg fibers, and you typically put them between the +/-45-deg and 0-deg fibers. Sometimes I put some 90-deg layers equally distributed throughout the laminate.

All of these factors will determine the final laminate overall strength and stiffness. These are best confirmed by tests. Masts will typically fail in compression, so compression strength and modulus are the primary engineering numbers to design to and test for.

I hope that sheds some light on mast design from my point of view. Thanks for asking me to comment.

Eric

 

[Eric Sponberg]

I should add one more comment on fiber volume, which I neglected to cover. Typically in boatbuilding laminates, we deal with fiber weight instead of fiber volume, because it is easier to measure ratios of fiber weight. In boatbuilding laminates with room temperature cure, fiber weights of 40-50% are typical. In vacuum bagged laminates, it is possible to get 50-60% fiber weight. In infused laminates, it is possible to get 60-70% fiber weight.

According to my design charts, the following are conversions from fiber weight to fiber volume for unidirectional epoxy laminates (you can interpolate linearly between these numbers):

E-glass:
40% f.w. (fiber content by weight) = 22% f.v. (fiber content by volume)
50% f.w. = 30% f.v.
60% f.w. = 39% f.v.

S-2 glass:
40% f.w. = 23% f.v.
50% f.w. = 31% f.v.
60% f.w. = 40% f.v.

Kevlar:
40% f.w. = 34% f.v.
50% f.w. = 43.5% f.v.
60% f.w. = 53.5% f.v.

Carbon:
40% f.w. = 29% f.v.
50% f.w. = 38% f.v.
60% f.w. = 48% f.v.

So, we are nowhere near what the aerospace industry is capable of, but we still build respectable masts and boats.

Eric

 

[Inquisitor]

water addict: "poo-poo score 1, I told you so score 1, constructive criticism 0"
Eric: constructive criticism 10! Thank you.

Thanks Inq, I'm still wating for specs, but I did find a few sites that are interesting...

I’ll be reading your sites today. I’ve also sent an email to several fiberglass/epoxy vendors and baited them (a 20’ and 40’ cat… they will be counting the tons of material going out the door.) Capitalism might bring answers.

However, Eric’s dismal description of the state of the art has winded me. His “optimistic” 39% E-glass fiber volume has frankly staggered me. In fact, it was so bad, I had to go back and triple check my source and went so far as to check the theoretical maximum fiber volume again. Theoretical maximum is 90.7%. On several projects we even went to extra trouble to get better than the 78% we normally held standard.

Conservatively, I think you will have to consider going the Carbon or Aluminum routes.

Radically, I’m challenged to keep going… and will. I see at least three things in the normal hand-lay-up method that hinder fiber volume. However, I have to convince myself with actual hands-on experience with some techniques I want to try. I could and would not expect anyone to take a glass/epoxy analysis seriously without a real-world verification.

Several things I would ask:
1) What is your time-frame for starting fabrication of a composite mast?
2) What is your time-frame for purchasing an aluminum mast?
3) What brand of glass and epoxy based resin would you most likely prefer? I would rather not consider poly and vinyl resins.
4) I’d still like those properties when you get them.

 

[water addict]

water addict: "poo-poo score 1, I told you so score 1, constructive criticism 0"
Eric: constructive criticism 10! Thank you.

.......

Guess the truth hurts sometimes.

 

[Inquisitor]

Guess the truth hurts sometimes.

Nah, not really!

I make mistakes and learn from them. But in this case, the project is far from over. The only goal is to make something lighter, stronger, stiffer, cheaper and I'll even now throw in... less heeling windage (at your ominous prediction)(with the recommended safety factors) than the aluminum mast that Robjl was planning on using.

But really… if you have nothing better to do than just criticize without actually sharing any knowledge... well... I'll let everyone else fill in that blank.

Excerpt from your bio:
Current Boats:
use others at their expense!

Says a lot about you. Why don’t you part with a little of your own cash that hoarding your great wisdom has made you. Put your money where your mouth is and build something and go sailing and leave us to try and help each other out.

I, at least, will be sailing my designs. And maybe (or maybe not) even a G/E mast someday.

 

[Robjl]

The breeze is picking up!

Thanks to all for your ideas, here's mine,
(Using my 240 x 160 oval) .. I think this is about the right size in Alloy:
I think the mast should be hollow:
This allows for internal halyards and also allows us to use all the ready made bits we use in Alloy masts. These are also reasonably priced.
If the mast has a foam core (32Kg/cu-metre) the core would weigh 17.9kg!
If we used 16mm thick timber (.625") the timber (say 300kg/cu-metre) mast would weigh 44Kg. Maybe this can be glassed and will work but I don't like the potential for rot in the timber.
I favour the hollow:
I think I could build a male mould that would do the job.
See if this makes sense?
The mould would be a bit wider (about 25mm/1") than half of the major axis of the oval. Like an upside down "U" with slightly flattened sides. The length would be 300mm/12" longer than the height to the lower spreaders.
In other words a male half mould of about one third of the mast length.
This would be of any straight grained timber laminated up, well supported. The timber finish (plus/minus 1mm) would be fine, epoxy spray putty, sanded off with 180 grit would be adequate.
This section I may make parallel except for 600mm (at the spreader end) which would be stepped down (recessed) by about 2mm. This will be the area of overlap at the spreader and shroud connection.
After mould release I would lay up one layer of 750gm double bias stiched glass fabric, apply peel ply and squeegy out excess resin.
Maybe post cure. When cured this moulding(#1) would easily pop off the mould. Then Fit #1 to the underside or my mould overlapping by 50mm.
The mould is now supported with say three 10mm dia horizontal bars.
I'm concerned here that the #1 moulding may tend to curl up and here I ask for opinions ...anyone??
Re-polish the mould and then glass up the top again with 750gm double bias.
I now have a lower section of the mast with a doubling of glass over 50mm at the sides.
Weight of this extra is 17mx2sidesx.05m widex1.5Kg =2.55kg for whole mast.
Remove the support bars,use the gentle persuader to loosen the #2 moulding.
Anyone?? will it be stiff enough to handle' I thing it may be a bit floppy??
Next re-polish the mould and slip the #2 moulding on to overlap by 600mm.
Glass another half with 600mm overlap, this gives extra thickness at the spreader/shroud area.
Pop it loose, turn it over, glass another half... and so on. Each time reducing the length to suit spreader positions.
When glassing up the final section I can trim off a tapered part of the flat on the sides of the #5 moulding so that the major axis of the top section will taper to about 200mm max.
This is my basic shape, I can support this with horizontal bars through where connections will be anyway.
This I can then add to with 90Deg (hoop strength) say 200gm then Unidirectional say 2000gm, then the 200 @ 90Deg, and finally 750gm of double bias.
I think I can "practically" achieve the above in a number of ways:
BUT:
I'm guestimating the layup!!!
I would make a test section about a metre long.. the materials to test the process are relativel cheap.
Would I resin Infuse,??
But as you can see I'm already up to the weight of an Alloy section?
As soon as I get some figures I'll post them.
Comments please.
Regards to all,
Rob.

 

[rob denney]

carbon masts for amateur builders

G'day,
We design and build carbon masts up to 60'/18m long. Primarily unstayed for proas (http://www.harryproa.com/) but also stayed for a variety of other boats. We also sell plans for amateur builders which include how to build your carbon mast.

I disagree with a lot of what has been said about carbon up until Eric's response.

Some points in no particular order.

A carbon mast will be about 60% the weight of a standard alloy one, less if it is engineered correctly as you can alter the wall thickness and the section shape. Further weight savings come from carbon fittings and bonding instead of mechanical fastenings. For serious weight and cost saving though, make it unstayed. These weight savings are not just about boat speed. They also reduce heeling and pitching, making for a more enjoyable ride.

Carbon/epoxy is remarkably tough. I have dropped masts off trailers and roof racks without damage. Think of Formula One cars, hockey sticks and fishing rods, all of which receive abuse which alloy could not cope with.

A foam cored carbon mast is a waste of time, unless it is a large chord wing mast. The amount of carbon required for strength and stiffness means there is enough material for panel stiffness.

Carbon is not expensive. We paid $US7.70/lb for our last order, which admittedly was half a ton. There has since been a worldwide shortage, so I am not sure what it is currently available for. We are happy to sell at our bulk buying price when we can get it. There is much less resin (about one and a half times the price per lb) in a carbon mast and much less labour compared to glass. Resin selection is important. A long outlife room temperature cure epoxy with mild post cure (about 60 degrees C for 24 hours, which can be achieved in the sun very easily) will allow for a clear black finish with heat distortion temperature of about 90C which is what shiny black surfaces get to on a very sunny day. We have never had any carbon/resin problems relating to differential expansion.

We use tow. The bundles of fibres that make up the strands in woven or knitted cloth. This eliminates expensive and damaging processing by the manufacturer, and eliminates cutting from the build process. There is almost zero waste with tow, compared to a huge amount using sheet material on a tapered mast.

Quality control is essential, but a careful amateur laminator will be within a bull's roar of an autoclaved result in a temperature controlled environment.

Safety factors are a misnomer. They are fudge factors to allow for unknowns. These unknowns are primarily the loads, fatigue and manufacturing process.
We test samples of the laminate we are using and use these numbers for the masts. Manufactuirers numbers are useless for determining final laminate properties. Unstayed proa mast loads are very easy to calculate as there are no holes in the masts, flogging sails, violent broaches or peculiar spinnaker pole loads.
Long term fatigue degradation of carbon/epoxy laminated properly is better than any other material except wet wood (ie trees) according to the Gougeon Brothers who ran extensive tests. Taking all these factors into account, we use safety factors of 2 for cruisers, 1.5 for racing masts. We also bench test our masts to ensure the flex properties are as per specification.

Our amateur process uses carbon strips, laid up under 3 atmospheres pressure using a vacuum pump. Details of the process can be seen on http://www.harryproa.com/building_hg/buildinghg_wk14.htm and http://www.harryproa.com/building_hg/buildinghg_wk15.htm

Our in house technique uses no expensive moulds or mandrels, resulting in masts about 2/3 the price of any other manufacturer.

Sail tracks on carbon masts are usually built in (bit tricky, needs high pressure), bonded on (split tube) to small masts or mechanically fastened to large masts. We have a bond on carbon rcb track with plastic cars which is suitable for boats to 50'/15m. This eliminates the dissimlar materials problem and the extra weight of alloy track, stainless bolts and alloy backing plate, all of which need insulating from each other and the carbon.

Laying up more than about 200 gsm/6oz of carbon on a flat table and bending it to a mast shape is impossible.

I have taken a few descriptive short cuts to keep the post short. If anyone has any questions on any of this, please feel free to ask.

regards,

rob

 

[water addict]

Nah, not really!

I make mistakes and learn from them. But in this case, the project is far from over. The only goal is to make something lighter, stronger, stiffer, cheaper and I'll even now throw in... less heeling windage (at your ominous prediction)(with the recommended safety factors) than the aluminum mast that Robjl was planning on using.

But really… if you have nothing better to do than just criticize without actually sharing any knowledge... well... I'll let everyone else fill in that blank.

Excerpt from your bio:
Current Boats:
use others at their expense!

Says a lot about you. Why don’t you part with a little of your own cash that hoarding your great wisdom has made you. Put your money where your mouth is and build something and go sailing and leave us to try and help each other out.

I, at least, will be sailing my designs. And maybe (or maybe not) even a G/E mast someday.

Spare me the lecture on my sailing knowledge and habits. I'll pursue the sport in my own way, you pursue it in yours. Actually I do own a boat, but was trying to be humorous. Must have got lost in translation.

I thought I was sharing my knowledge at the outset, stating that you would make a lighter mast out of Al. than glass/epoxy. It just was not what you wanted to hear- so we degrade into personal attacks? I also said if it would be fun for you to make one anyway, go ahead- I don't care. As far as my "truth hurts" comment it was meant as toungue in cheek, so lighten up.