Carbon fiber spars

[bobmcgov]

Yet another incredibly expensive racing boat dismasted due to failure of its carbon mast or boom. Seems like every major race -- the last AC, the MiniTransat, the Middle Sea -- several boats are losing their spars.

Remember when people tried to build mountain bikes out of carbon fiber? It didn't work so good. Sure, it was stiff and light, yet with a certain amount of helpful flexion -- but the frames had a nasty habit of disintegrating at inconvenient moments. Friend of my roommate got a nice payoff from a bike company after his carbon-frame bike crumbled in the midst of a downhill run, breaking about half the bones in his body. Oops.

It seems the stuff fails internally, due to a strain/shear delamination. Maybe perfect manufacturing techniques could fix that, or maybe it's intrinsic to laminated constructions where the mat or roving all runs parallel to the spar, but none interlocks the layers?

How common were spar failures when aluminum was the material of choice, compared to carbon? Sure, reducing weight at the masthead is a priority to reduce moments of inertia -- how about a mast that's aluminum for half its length, then carbon above? Just curious whether you think this material is here to stay, or if carbon spars will go the way of carbon fiber mountain bikes.

[Sailormann]

Giulietta may have some thoughts on this for you ...

[7Psych]

Tartan Yachts uses carbon fiber for all their spars. I believe C&C does as well.

[Jeff_H]

Actually, spar failures are way down from the bad old day of spagetti aluminum spars. Back during the IOR, late MORC, and early IMS days, aluminum spars had gotten tiny and failures were quite common. The rigs of that period were so fragile that short-handed sailing on larger leading edge boats was nearly imposible.

Because carbon fiber spars are so light for their strength and so can have higher safety factors, initially, they actually tend to be much stronger and less likely to fail than the aluminum spars that they replace. Carbon fiber spars have had an excellent safety record.

Its not that carbon fiber spars are without some liabilities. They do take greater care in their fabrication, expecially in the methods used to make attachments to the spar.

Carbon Fiber is more fatigue prone than aluminum and so potentially carbon spars have a more limited lifespan. That said, back in the late 1990's, I began hearing projections of 20-25 years for the early carbon fiber spars. That proved to be too conservative with many early non-grand prix carbon fiber spars approaching 30 years of use and still holding up.

One of the rarely discussed potential liabilities of a carbon spar is the impact of a lightning strike, which alledgedly, depending on who you believe, can greatly reduce the strength of the spar and accelerate fatigue.

The last issue is ease of repair. Carbon fiber spars are harder to repair than a damaged aluminum rig which may be repairable. This last issue may be a bit of a red herring since damaged aluminum spars seem to be repalced rather than repaired these days.

Jeff

[ronbo1]

In the last couple years there have been carbon mast failures of some high profile boats/ people that hasn't been widely publicized.

Oyster Company's owner lost his mast on a rally to Antigua.

A Morris 45' skippered by Cuyler Morris was dismasted off the FL coast.

I believe it was reported that wind conditions were minimal at the time.
Makes you wonder...

[Bardo]

Freedom has been using them for 25+ years with few problems.

[sailingdog]

Saying that the carbon fiber masts on a racing boat broke, makes them a bad idea for all boats is generally a bad generalization to make. Racing boats generally have lighter masts for the size of sail than do production boats. Racing boats also generally have lower safety ratios than do cruising boats, and are generally pushed harder, so are more likely to brea hardware.

The early carbon fiber bicycles were made when the fact that carbon fiber tends to be very unidirectional in resisting forces wasn't really understood... and that lead to bicycle frames that would collapse under the stresses of cycling if the frame was scratched in the wrong place. That really isn't the case anymore, since the material has been used for decades now, and is fairly well understood now.

JeffH mentions the issue of lightning strikes... the problem is that graphite is relatively good at conducting electricity, but the laminate heats up quite a bit if exposed to a high current and voltage, and the heat can cause the spar to delaminate internally, where the damage is not going to be visible—leading to sudden, unexpected spar failure.

[ccriders]

I've had several years experience with carbon fiber as used in bicycles. The repair, maintenance and face to face with customers experience, as opposed to design and manufacture experience. From that experience I believe that carbon fiber masts and booms can be designed and manufactured so as to have a virtually infinite fatigue life, could greatly reduce weight, increase strength and allow more sophisticated airfoil shaping. the only real issues for a sailboat will be the manner in which attachments are made to the spar. Galvanic corrosion will be horrid unless meticulously addressed at every stage of design, manufacture and installation. Penetrating the carbon structure will corrupt its integrity unless done exactly right. Attachments merely bonded to the surface will release and attachments that penetrate the carbon will introduce galvanic corrosion and other damage to the structure.
The bike industry did some fatigue testing on handle bars; light weight aluminum bars, carbon reinforced aluminim bars and all carbon fiber bars. The bars were fixed at the center and cyclically loaded at the ends. The aluminum bars failed quite rapidly (17,000 cycles as I recall), the carbon/aluminum bars lasted about 10 times as long and the all carbon bars showed no signs of fatigue stress after several hundred million cycles. The testers then tried to see what it would take to break the carbon bars by accellerating the load in free fall for about 25 feet then stopping the center of the bars on an immovable object, the crash test in other words. It took several iterations to break the bars.

Carbon fiber is remarkable stuff and would make great spars for racers and cruisers who have a much bigger pocket book than I.

[bobmcgov]

OK: so there seems to be a pretty strong agreement that carbon fiber is a good material for masts and booms, and it can be both strong and durable. So what accounts for the high-profile dismastings and boom breakages?

a) Uneven manufacturing quality, or difficulty ensuring a given spar's tolerances.
b) Racers demanding spars perilously thin to save weight (jiggering w/ safety factors).
c) Insanely abusive conditions during ocean races -- any spar material might fail.
d) Poor rigging decisions, compromising the spar's design strength.
e) Just more media coverage. Spars have always broken, but now we can see it on YouTube.

[sailingdog]

Bob-

I'd say that pretty well covers it, especially answers b, c, and e. Maude Fontenoy broke the mast on her circumnavigation earlier this year, but I believe her boat was using more traditional aluminum spars. All spars can break... better designed and implemented ones tend to break less.

EDIT: maud's boat did have a CF mast.. I just checked on her website.