Update
to do damage to the structure, and with each new generation of Imoca the speed is increasing. But the choice of material is another contributing factor in some cases. The new boats that failed are a worry as whatever reinforcement
was done around the bottom before the start was not enough to deal with the shock loads when sailing fast in high seas. Epoxy carbon fibre composites have a high strength in tension and very high rigidity and they transmit shocks very well without damping them. CFRP composites are also notorious for their lack of plasticity meaning they break without warning. By comparison, older carbon fibre composites will often elongate more before they break, grp and metal even more so. The better propagation of shocks may explain the failure of
internal structures propagating far away from the slamming area (this is suspected to be the root cause of PRB’s destruction – ed). The use of a mix of carbon fibre with aramid (Kevlar type), high- density polyethylene (Dyneema type) or even glass fibres rather than 100 per cent carbon fibre composite would certainly reduce the sensitivity of the structure to shock loads by providing the structure with a plasticity domain and a tolerance to damage. For the skin of the bottom of a boat or any water-slamming area,
some years ago I explained in Seahorse the reasons why honey- comb should be banned. Foam sandwiches are less risky than honeycomb but can still collapse locally when subjected to trans- verse impact load and that failure can easily propagate. In all areas subjected to slamming and impact on flotsam, mono-
lithic skin construction with mixed fibres are preferable for safety, even if it is heavier than sandwich construction. At least it provides a more ‘bulletproof’ shell to stay afloat (for bulletproof vests and armour shields both Kevlar and Dyneema-type fibres are commonly used, never carbon fibre. Is that a lesson to be learnt?). Another dangerous load case is that of CFRP shell skins sub-
jected to dynamic compression load associated with transverse load. Their strength is much more limited than when subjected to similar tension+transverse loads for two reasons: one, carbon fibres have less strength in compression than in tension; two, skins in compression are susceptible to buckling. That difference between compression and tension can explain
the catastrophic failure of PRBwhen diving into a wave. The forward deck and side panels were subjected to serious longitudinal com- pression loading as the boat penetrating the wave slowed down, with transverse loading due to the dynamic water pressure. The solution to this is to have more internal structure beneath
the skins of the forward area, engineered to take the fore-aft compression load in a stable manner even when the interspersed skin panels flex and so lose their compression stiffness. One should recall that, for structures in compression, looking to the resulting Von Mises Stress to determine the margin of safety is not sufficient to ensure the stability of the structure as a whole. An interesting load case is that of Samantha Davies’ Initiatives
Coeur hitting a UFO with its keel. This is not the first time this has happened to offshore yachts and this failure mode is distinct from the previous cases. The keel well and adjacent structure suffer a local overload starting around the pivots of the keel. The problem stems from the hard mount of the keel pivots which
have zero energy absorption capacity. A solution for canting-keel boats like the Imocas is to mount the pivots of the keel with pre- loaded springs or rubber blocks which ensures the keel pivots are held in position under normal circumstances but can move if the preset load on the rear pivot is exceeded. That movement of the rear pivot (back and up) will reduce the peak load seen by the sur- rounding structure, a bit like the suspension which limits the loads on the car structure and passengers when on a bumpy road. Robert A Lainé has over 50 years’ experience in aerospace, space and satellite technology, including developing vehicles to access the International Space Station, orbital telescopes and communi- cations systems. He is also the founder of Spacinov, creators of Desalin, a solar-powered large-scale desalination system. He holds upwards of 18 patents, most relating to space technology. And Robert is a longstanding member of the RORC…
18 SEAHORSE SNAPSHOTS Brought to you in association with
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l Whoaaa…BREAKING NEWS!! l Against expectations…Stars&Stripes have withdrawn from the Cup l PS…check out the minimum number of entries to ensure NZ government funding (whoops-ed) l What goes around…when Jean Le Cam lost his keel and capsized at Cape Horn in the 2008 Vendée… l He was saved by…Vincent Riou l Onboard…a boat named PRB l What goes around again…Macif won the 2012 VG having drawn Argos beacon reg 600051 l Banque Pop…won the 2016 race carrying... l You…guessed it l 19…and one... l That’s…19 capsizes in the American Magic Mule l Plus…one in their first AC75, Defiant l Gotta…admire ’em (we do, biggly) l So about…that big Fastnet change... l Specifically…our point that all boats get faster... l In 1925…Jolie Brise won the Fastnet in a little under seven days l In 2013…she completed the course in less than five days l So can we… cope with an extra 90nm? l Yes…we cam (sorry) l Boggling…11 different leaders of the Vendée Globe by mid-distance l And…five boats within sight of each other in the Southern Ocean l So many stats…but most are pretty impressive... l Forty-one… TV stations covered the Vendée Globe start live… l Broadcasting to…190 different countries l In France…4.1 million viewers watched live too (23 per cent of national audience share) l America’s Cup…oh, where did it all go wrong? l How long…ya got? (ed) l But will…those (fragile) foiling Imocas end up like budget rentals? l No more…than 500 miles per trip please, sir l Time…for a Figaro 3-style record system for critical components? l Especially as…19 foilers started the current VG with 25-30 expected in 2024 (cripes, Moriarty) l Imoca sailors…have different values l When… Thomas Ruyant heard a soft crack on LinkedOut… l He would have…much preferred a loud bang l One says collision… and we get that l The other suggests… an ongoing structural failure l AC75 Code Zeroes… they designed and built ’em, for sure l Instant obsolescence…now they are just ballast l But for good reason…they’re too bloody fast l So fast, in fact…that without a four-outboard rig folks in Kiwi have learnt to kiss ’em goodbye l Lots of talk…about a Japanese-flagged freighter losing more than 1,500 containers over the side l Which is bad karma…but we surely all know that’s not what the Imocas have been hitting? l Nice one…although it’s called the America’s Cup l And…the US team is a good bet for Challenger l To watch…the action in the US you have to pony up $175 to NBC l Luckily…for everything/everyone else there’s YouTube l Welcome home…naughty Hugo Boss had their knuckles rapped in court when they were told they should have paid their foil builder... l Bad boys…plus costs (and one unimpressed judge) l Fashion victim… a boom-deck endplate on a Maxi in Australia l Ickle bitch…the UK’s idiot scientists running project fear have ‘proved’ that if the world had locked down after the Yalta Conference of 1945 then no one else would ever have died from anything l Caught the… Oracle Cool-Aid? l The Cup organisers…had a go at introducing a ‘don’t be mean to us’ clause as a condition for media accreditation (naah) l Huge congrats to…Gilles Martin-Raget for winning the Mirabaud Yacht Racing Image of the Century with his shot of the Fuji Orma 60 tri barely visible in giant waves as she rounds Ushant in 2002… l And to Pete Burling…awarded the Magnus Olsson Prize for 2020 for an outstanding contribution to yachting l For shopping…
RaceboatsOnly.com l For everything else…
EurosailNews.com
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