Pictures of Americas Cup-class boat hulls breaking in half and their masts, supported by a plethora of rigging and spreaders, collapsing in relatively benign conditions, have given structures built of carbon fibre an undeserved reputation for fragility. But it should be remembered that Americas Cup boats are designed on the ragged edge of structural engineering where the motto is “if it does not break occasionally, we built it too heavy”.
The facts are that a cruising mast properly engineered and built in carbon is stronger, stiffer and less susceptible to fatigue than a mast built in aluminum could ever be. And all this at about half the tube weight of an aluminum mast.
John, When we met in Charleston you mentioned once in to me that your rigging size had remained the same (or even increased?) when changing from Aluminum to a Carbon mast. So the total weight savings in a change from Aluminum to Carbon mast is “only” in the actual mast and NOT in the rigging. Is that correct or did I misunderstood you?
I am not too familiar with carbon, but I guess due to the increased acceleration forces by using a carbon mast the rigging size has to be increased (or remains the same when changing from Aluminum to carbon, bus as weight decreases of mast you can say rigging weight % wise increases.)
How did Mast Weight versus rigging Weight compare on Morgans Cloud with Carbon?
Hi Peter,
The important thing to understand is that if you make your mast lighter, no matter the material, the loads on the rigging go up, not down. Counter-intuitive I know, but true. The reason is that the boat’s stability goes up with a lighter mast and therefore the maxim righting moment, which is the number engineers use to size rigging, goes up as the rig gets lighter.
This post has a complete analysis of the weight savings of our new rig and the real-world benefits thereof.
http://www.morganscloud.com/2008/12/18/new-sailboat-mast/
I’m sold onthe benefits of a carbon mastfor all the reasons discussed, the one question I have is how one assesses the potential damage caused by a lightening strike, as unlikely as a strike might be. The carbon spare is basically a long resistor and there will be significant heat build-up during a strike causing any resin-trapped air to expand and possibly cause fractures. Does a grounding wire sufficiently shunt and protect the mast in such situations?
Geoff Jenkins
Hi Geoff,
We have an in-depth chapter on just that here.
John,
I understand that you didn’t replace the boom with a carbon boom, since yours was still very usable. But if you were to spec a new boat, would you spend the money on getting a carbon boom as well?
Hi Daniel,
The only reason I would spend money on a carbon boom would be to get the benefits of a pocket type boom, which is not practical in aluminum. Otherwise the weight benefits down that low don’t justify the price increase of carbon.
The Alloy mast was replaced after 25 years and 120,000 miles. Replacing like-for-like would have cost $30k. This gives $1,200 per year or $0.25c per mile. How long is the $55k carbon replacement expected to last?
Hi Paul,
I’m no expert on composite construction longevity, but given that our mast was intentionally overbuilt and that Carbon does not fatigue, I would guess that the answer is pretty much indefinitely.
The other point is that our original mast had joint at the partners, which was the root of the problem, so it’s not really valid to draw any conclusions about aluminium mast longevity either.
Do you think a carbon mast could also reduce drag aloft? Perhaps it can be made thinner for the same strength. This would seem to initiate another virtuous circle in terms of windward ability. When reefed down and clawing off a lee shore it would seem advantageous to have a skinny needle aloft rather than a relatively fat pole.
Please delete this comment. You’ve already answered it. And I’m getting forgetful.
https://www.morganscloud.com/2009/02/01/carbon-fibre-mast-costs-and-benefits/#comment-298047
Love the idea and the benefits. Can’t afford it. I hope you might comment on the loss of a carbon fiber mast reported in April 2023 Yachting Monthly. A 54’ Grand Soleil. Mast buckled at the gooseneck.
Hi Terence,
Hadn’t heard of that one and can’t find anything online. That said, even if I could I’m not sure I would have anything useful to say about it other than any structure can fail if the either the engineering is inadequate or the build does not conform to the design, so I would guess one of those was the problem given that you can build a stronger and more robust mast for a given weight in carbon, so the material itself would not be to blame.