I try to surf the SA Forums as often as I can because there is sometimes some wheat amongst the chaff. There’s always entertaining debate and it’s interesting to see what the ‘grass roots’, the sailors are following and ‘care about’ most. Sometimes of course there’s a great deal of intolerance, but it’s an open forum so if you don’t like it you can always opt out and not take it too seriously. I only once recall being pissed off and pitching in to head off an un-called for attack on someone whose input I thought was reliable and/or invaluable to sparking debate.
Anyway, this is probably my pitch in for the year. Re: slamming areas on Volvo 60’s and 70’s.
Re: Open 60’s, some facts:
OCD: are all Corecell foam in the slamming areas, that includes Acciona and goes right back through our other seven sixties to Kingfisher, although the grade, density and thicknesses have varied boat to boat of course. Never a problem with delam, but it’s not the same dynamic as the Volvo 70’s – as with many things sometimes it’s an unreasonable thing to draw comparisons between classes or even different designs within a class. People, projects, teams often tend to do things for reasons that may not be immediately obvious to outsiders (including other project teams/designers) and there is always the potential for some projects to follow the crowd (fashions in hats as I describe it), be that for the good, or bad. We’re always willing to use someone else’s good idea, but where applicable we always strive to prove or disprove it for ourselves rather than adopting it blindly.
Farr: Conceptually have always had foam in slamming areas, I can’t say if always Corecell, but that’s certainly been the foam in some of the boats. Perhaps they sneaked some high density Nomex in some parts forward but it would be a surprise to me if they weren’t predominantly foam and 100% sandwich below the waterline forward of the keel.
Finot: Since Giovanni Soldini’s boat way back in 97, monolithic, with the exception of Hugo Boss for Alex, which was a collaboration wtih SP Gurit . She’s Corecell if my memory is correct. A person from within the project/design team may put me right on that. I didn’t take pictures when I had the tour from Alex. When we built the Finot designed Team Group 4 we had to push hard to have Nomex core aft of the keel area as it had been the practice of the Finot office since PERHAPS Cacolac Acquitaine to build monolithic below the waterline from front to back.
Guillaume: All his boats have been monolithic forward of the keel. It’s his belief system and their are perfectly good reasons to go that way. It’s a choice, but not our choice.
Juan: Pindar (which became Hugo Boss 3) was sandwich, I couldn’t say about the Bernard’s new boat, but I suspect sandwich – Nomex or foam I wouldn’t know for sure.
Marc: He had success with the first Sill which was high density Nomex in the slamming areas and we always considered that a pretty ballsy move given the weight saving available and how low down in the boat it was. I don’t know if later versions of Sill/Bonduelle were Nomex or Monolithic but they wouldn’t have been foam because these boats (as per Team Group 4 and the three boats that came out of her mould) were built from 120C pre-preg in a female mould at JMV and no foam cores survive that temperature.
That opens another conversation doesn’t it? So, it’s not easy; there are design, build, philosophy, engineering and material choice issues that can drive the construction of the forward end of the boat. It’s not always as simple as one might think why any one designer, or builder for that matter ( it would be in our opinion a brave designer/engineer who forced a builder to change for the first time their methodology and the materials that they know well, in order to facilitate a particular practice and materials they prefer) chooses a particular method/materials to build a boat..
In summary, openly, but rather controversially and of course to some extent with some dissatisfaction I believe the following is true:
1) Designers and engineers continue to learn year after year about slamming effects on high performance sailing boat hulls. It just isn’t a simple exercise and the calculation of forces are still not FULLY understood by classification societies, or even the designers of naval vessels, fast attack craft etc who have had far greater budgets and much longer to develop the numerical tools and emperical knowledge than designers of high performance sailboats. Engineers and academics continue to find more about the effects of hydro-elasticity on the pressure fields and peak pressures created by slamming loads on panels and the associated point loadings. Research continues and is funded by national bodies and commercial concerns with means beyond the reach of any single yacht design or engineering house. In addition the manner in which a panel reacts based on the stiffness of the edges (bulkheads, frames, longitudinals or chines) is still the subject of research and recent papers from academia. Like it or lump it we don’t know everything and we’re pushing the edges of what is possible and obviously the sailors are pushing the edges of the envelope that designers and builders create.
2) Now, in our profession’s defence, we’re not complete numpties either and you should believe I think as I do that none of the designers/engineers of this Volvo are sending their boats out on a Round The World Race having tried to save the last few kg in the hull shell. We all know the history as well as the public does and the mantra that “to win, first you have to finish” is as well known to us as it is to the reader of any sailing website. We do however live in a competitive world and sailors expect their boats to be the fastest in the 0 to 25 knot wind range. More on that below. You may also be surprised to know that in many areas of the boat’s design; rudders and slamming areas in particular we certainly well exceed scantlings that would be required by ISO, ABS, Germansker Lloyd etc simply because these would be insufficient in the world of Volvo 70 or Open 60.
3) One reason why is: In SIMPLE terms (please don’t attack this attempt to put a very complex subject into layman’s English), the pressure/force induced on a body once it’s immersed in a liquid is a first order equation. That is, the increase in force is linear to the depth of the body immersed . But the force of driving an Open 60 or Volvo 70 into waves is second order, such that if the relative impact of a boat into a wall of water is 10 kts the force is 10 squared = 100, 20 knots the force is 20 squared = 400, 30 knots, 900 and 40 knots (remember Rob Greenhalgh reported doing 40+ kts on Abu Dhabi – and that doesn’t allow for the relative speed/angle of the water that hit the boat) = 1,600………You can see the challenge here for structural engineers, designers. Sailors want a competitive boat and require it to be fast in moderate conditions, light, low vcg etc. but in these conditions the boat is only doing 15-20 knots. Indeed the average speed of an IMOCA 60 on the Vendee Globe is only 13 kts, but speeds of 30 to 35 kts and then dropping off waves are well documented in this class and all this under pilot which is fearless and doesn’t even try to bear down the wave crest (if there even is one).
4) As I heard first hand in Auckland less than a month ago, sailors from numerous teams are well aware that you can break a Volvo 70. They are very fast and force as we see force can be equated in simple terms to boatspeed squared. When that force is applied to a panel, well there are a whole number of variables that are hard to compute: speed of wave, height of wave, relative speed of boat, pressure distribution of the slamming area. Then each panel will react differently based on how it’s supported in it’s four axis (a simple case) and depending on the longitudinal and transverse curvature. I haven’t even begun to cover the variables or the unknowns such as how hydro-elasticity really affects the global and peak panel loads. If the panel has some flex then in the same scenarios this can reduce the overall impact, but increase the local peak pressure) and if a panel is too well supported it can fail by a different method. This was not as well understood even as little as four years ago and research is still going on in this field.
5) Finally: Is what is built what was designed ? – Fibre/resin ratios, porosity, are only two of the many variables in a build process where EVERY boat is a prototype. Fifteen years of going around pre-preg build yards and there are as many different ways that individual technicians have developed to deal with the manufacturing process as there are ways of fairing/painting a boat. Each depends on local manufacturing conditions, experience, budgets, materials and there are always some who will claim their’s is the BEST method, but it’s unlikely at this level of the sport that any of the guys who work these processes are fools. When it comes to a Volvo or Open 60 is anyone seriously trying to win the last few kg out of the hull shell and trading that off against reliability? I doubt it, because the performance gains just aren’t there.
In summary, putting myself on the firing line so to speak.
Designers, engineers and builders don’t know everything – absolutely that accounts for some failures, but it’s a developing area of the sport and we’re not creating VW Golfs here and we don’t have anywhere near the time or budget of a an aerospace, production car manufacturer or Formula 1 campaign. How many years, millions of Euros and QA forms do you imagine it took to develop the carbon airframe of a Eurocopter or the latest Sikorsky? These only have to operate in one medium (air) and that’s a whole lot better understood than the seas that these boats sail in. Of course we all have to do a professional job, take responsibility for the work we do and hold our hands up if a mistake is made. If a hull, rig or appendage breaks is it reasonable to instantly point at the designer, engineer, product manufacturer, or sailor? Probably yes at least to start with, but be honest, how often is the first point of call the designer alone? Then perhaps someone remembers that maybe the design office didn’t engineer their own boat or that there’s a builder and a product manufacturer involved in the mix. Lastly someone is sailing the yacht. If the conditions are bad then for the designer it’s a saving grace because that’s always mentioned and there’s some or total allowance given depending on the severity of the conditions.
Designers and engineers make mistakes (that’s different from not knowing everything) – we’re human, but in my experience QA procedures are very good and if anything it’s more likely to be something designers/engineers don’t know that catches us out rather than a mistake.
It’s hard to know where the limit is and sailors can push over that limit very easily in a modern high performance yacht. You may feel that’s an unsatisfactory answer but when you were eighteen you knew taking that corner at sixty was a risk, you did it and you came a cropper – it’s a matter of understanding the limits and at sea that’s hard too do. It’s pitch black, you’re doing 20 plus knots and the front has just come through, seas are at 60 degrees to the new wind and you just know that you’re treating the boat hard. There’s a call to make.
So, sailors make mistakes too and/or they’re unlucky sometimes too. They’re racing at the limit and sometimes have to look after their machines in the same way as the guys on the Paris-Dakar Rally. This isn’t the Monaco Grand Prix with pit lanes out there. I’s not even the Le Mans 24 hrs race. In the case of the Vendee Globe it’s 28,000 miles non stop and no one has the God given right to finish, never mind get on the podium or win.
Nature is unforgiving and it’s not a mistake when after hours of regular controllable slamming the boat suddenly takes off over a wave with no back in it in the dead of night. That’s a sailor’s/skippers/helmsman’s experience that dictates how hard they push but occasionally they can be either lucky or unlucky in the way the boat falls.
If you want a boat that you can’t break then in average conditions you’re not going to be competitive. It’s as simple as that. If sponsors or the media want it another way then you have to change rules and the boat. But speaking as a designer and the skipper of a steel BT Challenge boat who pushed hard and broke a forestay and backstay (at different times, and kept the mast up and finished) I don’t have an answer as to how one can design a racing boat that’s impossible to break. That animal doesn’t exist in my book.
So, what’s going wrong with the Volvo 70 and why are we seeing so much damage? Well, in % terms it’s not very different I suspect from what we saw in the last Vendee Globe so far as drop out rates/1,000 miles. I don’t have an answer for you, only some facts I’ve provided regarding the original discussions regarding the cores in the bottom of boats along with some input above that I’m sure will spark more debate.
Finally, one could to some extent mitigate the risks in Volvo and IMOCA class by going fully one design (ike a BT boat. However, as I mentioned,. I guarantee you could still break the boat. There would be a price to pay as well if development classes ceased to exist in this risk adverse society. How boring our sport would be without foiling Moths, canting keels and without spin-offs such as PBO rigging and wing sails?
OK, this has taken far too long and this is my contribution for the year…..let loose the dogs of war and maybe I’ll take a breath at some point and come back and read the thread after this.
I have written before it is about knowing when to throttle back. If one remembers aboard “Banque Populaire V” during the recent successful record around the world; the helmsmen were told not to exceed forty knots in rough conditions.