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About SYDE

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  1. SYDE

    Best use of carbon for fast cruising cat

    Soma, which specific ISO regs and CE regs are you referring to? I have not scoured this thread as of yet, so excuse me if this is repeat info. To get a CE mark, a boat needs to meet certain standards. Unless my info is outdated, this meant adhering to the RCD Recreation Craft Directive. For purposes of structures, this leads us in almost all cases to ISO 12215. 12215 Part 5 of this ISO rule addresses hull scantlings below 24m hull length, basically 80 feet. But it is for monos and always has been. It defines w_os and w_is (dry weight of fibre for outside skin and inside skin respectively) differently for glass than for carbon. These two values are practically a minimum skin thickness. They are not very heavy, and I have gone through with a monohull that had a hull shell with 1.1 mm outside skin and 0.95 mm inside. 12215 Part 7 is for multis, and has been in development for ages. Still not officially in force actually. Anybody who wants to get access can via the working group tasked with preparing it, FIS. It takes an age because there simply is no real funding for a standard that has a fairly limited impact on worldwide product safety. I don't mind sharing this line from a Draft, hoping that I will not get in big trouble: "The requirements for bending moment and shear force are considered sufficient to determine core thickness and sandwich skins." In other words, in the draft version of Part 7 there is no minimum skin weight or thickness. They may well wish to add one, and I think it is in consideration for wet decks. Owing to the fact that ISO 12215 Part 7 has not been officially released, we started recently using the DNV-GL rules for Yachts, namely Pt3 (also sufficient to achieve compliance with RCD). Chapter 5, Section 7 includes this: "Apart from the provisions explicitly defined in this section, no particular algorithm has been implemented to define a minimum shell or skin thickness for hull laminates, covering wear and tear and local forces or impact, e.g. when docking, dry docking or from collision with floating or submerged debris." Now, I am not saying that the ISO 12215-7 Draft and the DNV-GL rules are not stringent on the basis of panel bending, skin buckling, core shear etc. I can say 1) they do not treat glass and carbon the same 2) they do not have a fixed minimum skin thickness without a basis on loading. And as such, if the loading is the same and the specific properties of carbon are significantly higher than glass fibre, which they are, you do save weight. Really.
  2. SYDE

    Route du Rhum 2018

    It would never be me. I could not do what AT or any of them does. But, after a short sleep, I think he should retire.
  3. I think the most interesting point is that DF is racing their polars. They need to focus on one main thing - boatspeed. A little care taken not to touch the bottom (4.8m!) but basically they are looking at the end of the race track in tunnel vision. They are fighting the clock and to a degree, the current. The western boats are racing each other in sight. That means they might get a pack benefit, but they can also miss a step on DF if they focus on the wrong things. Cudos to Mapfre for getting back in the group having kind of messing up the split. Plus, in close quarters, there is the small chance of team racing. A headfake by Akzo, or just pinching up a bit more than needed to spring the Brunel boat. What got Brunel here was just putting the hammer down. They need to sail their own race, IMHO, not easy to do with two boats in direct contact.
  4. Don't everybody lose their minds when the leaders have negative VMG. "where are they going? is the tracker broke?"
  5. Little bird told me the routing has DF 7 minutes from finish at the gun. That is going to be gutting. Anybody here have a "live" routing going?
  6. course 220 boatspeed 18+
  7. SYDE

    Sydney to Hobart 2017

    I also think the smartest would be for woxi to retire. It would always leave an asterisk on the win* of Comanche. Woxi is a legend already. To add to this they sailed, without any doubt, the best elapsed time on this course. I think it was a foul. I don't think any interpretation of the film evidence can say it wasn't, barring heavy 'financial' blindness. I think it can only be answered with dsq now after the fact. Time penalties are half measures at this point. If the time is exactly the difference what is the point? Just little enough to allow the win or just long enough to snub them. It is the same as no penalty or dsq. But I want to propose an interesting scenario. The jury knew from the next sched this could come. What if they decided the penalty and recorded it before the conclusion. As in 'the penalty shall be 10 minutes as of the info available on 27 Dec 1200, no matter the outcome of the race.' That would be a nice piece of cover to have in their pocket.
  8. SYDE

    Sydney to Hobart 2017

    maybe so, but it also a classy move to not impede the starboard tack yacht holding its course with an aggressively close tack. I think it will come down to the skipper. What will he want to be remembered for? And what past do the skippers have with each other?
  9. SYDE

    Sydney to Hobart 2017

    I would be surprised if this did not go to the room. Which is a pity.
  10. SYDE

    New imoca boats

    Sorry, not buying into the carbon = brittle argument. That is ancient, and has no bearing on properly conceived laminates. If you mean that unidirectional fibres have less strain to failure than ... fill in blank ... well that is true. But brittle depends on many choices. Kind of agree about absorption of energy but more in the skins than in the core. Something small and pointy will always get through if position is bad - it is a skin designed around the concept of normal pressure over an area. As for weight saving, I think the point of the design is to save weight, yes, but with the desire to remove the skin-core bond first and foremost.
  11. SYDE

    New imoca boats

    GBH, in the flat aft end of the VDS you see no such ribs. There is surely core there, whether more impact resistant high elongation 100+ kg/m2 foam or kevlar honeycomb, I cannot be sure. What I said about the usefulness of the stiffeners really does apply to the rounded areas below the chine and to the bow. I am not sold on the fault tolerance of this arrangement, but there is a fundamental logic there. I reckon they will bond the ribs back down and reduce their span by 1/2 (additional deep longitudinals over the top) and it will not be an issue again, unless NDT or samples removed show a fundamental gluing problem between rib and skin.
  12. SYDE

    New imoca boats

    GBH this is really a different structure layout compare to what we have seen of Gitana in photos. Gitana seems to be cored aft of the keel everywhere. Mental exercise - take a piece of plastic sheet, like a binder cover or something. Hold it so it has a radius of curvature in one direction. You do not need stiffeners in the the direction the is parallel, it has inherent stiffness IN THAT DIRECTION because of curvature. But you do in the direction that is in fact curved. Because in a thin sheet it is easy to make more or less radius, provided it is only in the one plane. The stiffeners in that orientation also conform to small panels edges in the fore-aft direction (where you will put more axial fibre for global stiffness). So, I also can generally agree with survivability of cored structures, usually. Engineered a number of high speed power boats with core all over, kevlar in the skins, and had good results. But if you have decided to eliminate the weak link in the chain - core bond - I can also understand this method. Note that unlike the Green build of HB, relying APPARENTLY completely on glued flanges of moulded frames (not bad) the Persico built VDS has relied completely on secondary bonding of covers over formers (just a bit better). Moreover, as to whether IMOCA should have concentrated or "one-designed" hull and deck structures, I disagree. For one, they should not. Nor should the masts or keels be so. This kind of step always trades real development for microscopic improvements at greater cost. For another, nothing is really changed, single skin hulls with frames is not new at all. If anything has been changed it has been reverting to transverse primary stiffeners, more frequent than before, and thinner skins. And to that point 3.5 to 4 mm thick doesn't much phase me. But 2.5 does. That seems really close to the bone. I have only done a bit of math on it, but it didn't look promising.
  13. SYDE

    New imoca boats

    These foil boxes/casings are anything but substantial. At least in the pictures I have seen. One end is attached to the hull and the other end to is supported by an end-plate that is connected to the floor and to nearby bulkhead. The hull connection should stand much more than the weight of the boat because of the force arm created by foil. The casing is quite short compared to the boat width or to the foil length. But anyway, uplift can be easily calculated. Foils are lifted out from the water by uplift and this makes the upper limit predictable. But in case of negative angle it increases progressively as the foil submerges. Some pictures of Gitana where the end plate is under construction: If the foil is under water (and it is designed to be fully) the only 2 ways that a significant about of load "increases progressively" is 1) with an increase is angle of attack (pos or neg doesn't matter, load is a linear function of CL which is approx linear with AoA until stall) or 2) an increase in speed (load a function of speed squared). Going deeper under water does increase hydrostatic pressure, but this is peanuts compared to the hydrodynamic. I have seen those images of the dagger bearing supports before. You can all it in substantial or not, entirely ones opinion. It is not any different to daggerboard exits or rudder bearing foundations, really. But, it proves my point, the foil loads are carried in a structure dedicated to this purpose. Reversals of load are not loading an otherwise unprepared hull shell. I see no reason to connect the presence of the foils to the structural issues yet. Certainly not from what was reported from HB by Alex and implied in photo from Virbac, both of which have everything to do with debonding or breaking of ribs. Alex is convinced it has to be an impact, though I think they may wish for a more fault tolerant system after refit. What detail (if any) is available on the other boats with structural issues?
  14. SYDE

    New imoca boats

    I believe the single-skinned hull solution would be good without mustaches and vice versa. Together these are recipe for catastrophe. The single-skinned hull concept is actually brilliant. It should work well under tension that rigging creates. Sandwich composite is heavier because the inner layer is useless ballast until it has to work against the deformation. Until that it is rather compressed and has to stretch a lot until it starts do work against the deformation. This allows more movement than pre-stretched single-skinned material. But because carbon does not stretch a lot the trick is how to get the tension spreaded evenly all over the hull. It is even more tricky with foils, especially in case of foil assisted solution that does not have horizontal stabilizers and rely on wetted surface to keep the correct angle of attack. In some cases, for example when the stern detaches from the water on top of a bigger wave, the angle of attack of the foil can go negative and it creates down-forces that work against keel counteracting forces. It might not feel as a big deal because it might not last long enough to increase the heeling angle significantly but it deforms the structure in the area that works normally under tension. It compresses the hull between the keel and the foil (both work opposite direction) and creates something like wrinkles in tension of the skin in the slamming area… I am not a structural engineer but I believe that this is one of many things that designers didn’t take into account in calculations. Sorry, there is no question that any designer working with foils also considers the load reversal due to changes in angle of attack. Moreover, take a very close look at the Virbac photo. I think we are seeing a lot of fibre running fore-aft on the inside skin under the broken stringer. The laminate is biased to fore-aft for global stiffness vs rigging loads (as you would do). So the foil lift loads, if not supported by internal structures, would be working at a normal angle to the fibre bias. I think however that if is too big an if. In my opinion the lift forces (ca. 6 to 8 tonnes) would have to be carried by the substantial foil boxes and/or frames not just the shell. Such a structure can also handle reversal of the load to be sure. In summary, I don't think the foil systems have anything to do with the photographed frame failure. Unless the damping to pitch was predicted and used to justify a lower dynamic load and thinner laminate. I am really surprised not to see obvious signs of unidirectional in the top of those very low frames.
  15. SYDE

    New imoca boats

    Yep. So which boat will be the first to sport L rudders, and fast!