JulianB

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18 Whiner

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About JulianB

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  1. I have spent many hours in what was then PSI and what is now LP, plus PSJ and PSA. I have been in the presence of 100's of Lasers being built. Firstly Styrene "flashes" off in about 2-3 hrs, its part of the cure cycle, gone long before the boat is ever taken out of the mould, so that's BS. It does leave microcapillaries, and salt dose gets into them. 2ndly, a Laser is a multi-layer construction, it is not 1 single layer of CSM. But sorry, it would be very unethical for me to go into the actual laminate schedule. 3rd thing Epoxy, unless you 2nd screed the surface, almost by definition of the vacuum process, you end up with dry laminates, nothing wrong with that, but you also end up with "wicking", which is water travelling up the fibres. Yes, even 49ers. which is why its so important to keep ANY boat dry. and well aired, pull both bungs out. Same is true of Farr 40's which is why they all plug-in de-humidifiers (sailed a Farr 40 yesterday, and final ritual is suck the water out of the pen, and turn the dehumidifier on.) I own a Farr 30, we always make sure there is no water in the bildges As for the construction of the Laser, its quite brilliant, and it has stood the test of time, well and truly, it has curved surface, which adds to it "form" stiffness, which a 29er/49er/Tasar don't have, so they need foam, sure, but a laser or just about anybody swung single hander has only "X" Righting moment, does not really matter which one, they are all roughly the same and that = about 4.5knts upwind or about 2-3 x that downwind. At that speed how far a hull deflects is pretty minimal. If you want to go faster, you put wings on, or get on the trapeze, Moth and Contender Musto, RS (sorry don't know the number) are examples, then you can get on foils and by the time you have got to that, hull is not in the water so stiffness is irrelevant. Polyesters, Vinylesters and Epoxies all have their places. Polyester is perfectly adequate for 29ers (and they go faster than 49ers) and Lasers, and a raft of other boats. 470's you're looking at trickier "ester" resin., To go to Epoxy, and foam core on a Laser, Btye, (even on a 29er) and 90% of "round bildge" the single handers is not really a cost-effective solution and you need only look at those that do go to the higher extents and look at their prices to see that's true. Horse for courses. Jb
  2. Sorry Major Tom, Tasar's are made from CSM and Polyester resin and they last for 30 years. 29er are made also from CSM and Polyester resin and they are not 20 years old yet but the laminate is not what is letting them down, its the kids pushing them at 30+ knts in HK that's causing them grief. Push any boat at 30+ knot's (Tasar's have been clocked at 25+) and you're going to have problems. For what the Laser dose, it laminate has stood the test of time, as has the Tasar, in a couple of years maybe the 29er can be added to that. Come up with a different reason, please!!! Jb
  3. Jib will fit. You may need to go up a hole in the clew board. The new spinnaker will be 100mm long in the luff, but I would not worry about it. it will be just a tad flat off the luff. jb
  4. JulianB

    World Sailing Vote ... Proposal M36

    Call it whatever you like. At least someone bothered to ring me up and get my side before spreading fake news. Timelines just don't add up. Sizes just don't add up. = Bullshit or fake news! Take your pick!
  5. JulianB

    World Sailing Vote ... Proposal M36

    when your done reading that crap, go read, http://www.impropercourse.com/
  6. JulianB

    29er

    The batten are heat shrunk for 2 reasons, #1, they are already sanded on a profile sanded and it to stop little dags coming out and buggering up the sails, and #2 to stop people tampering with the battens. So if a measurer finds battens with no heat-shrink, go buy another batten with it on. So no it's not class legal, in 29er, 49er & FX.
  7. JulianB

    29er

    I no longer feel qualified to answer this question. I use to believe that you bent the batten/sail at about 10%, so 1m long batten had 100mm of depth and you then tightened the batten until the wrinkles were just visible on the concave side. Lock it off, and you virtually never re-visited it. That was the right tension, across most wind strengths and it was very much set and forget. We put more than enough tension material in the sail that it can handle that sort of load indefinitely, so no need to back the batten off (99% of sailors never do) and I only did it if I took the sail on a OS flight or if I knew I would not be sailing for 6 months, which was just about never. Now I understand that people are fiddling with tension, depending on the wind-strength. We used to do this in the old days with dacron sails, but not sure how that works with Mylar, can really see the benefit and not sure which way you go with it so you will have to find out from someone smarter than me. What I suggested above would be a good starting point, and you can go from there. Jb
  8. JulianB

    29er

    Sorry guys, been a manic 10 days, HK, China, HK, Milan, Venice, Milan. With the wife in tow (leading me actually). By jack the mast aft, I mean, wedge it heavily under the LE of the mast so the mid mast, basically where the vang GN is, goes aft. Jb
  9. JulianB

    29er

    Mast heel wedge sets up the initial lower mast bend. Pretty simple, if you get any tube, stick a coin under the front edge, and then apply compression the tube will bend away from the coin. With a 29er, the wedge sets up lower mast "pre-bend", and that bend can be inverted. Nothing stopping you having reverse bend, but it's pretty spooky going downhill in a breeze with a kite, and you will more than likely break the mid-mast. If your light, you don't want a lot of pre-bend (negative) because you want the sail to blade open (leach open) early. If you heavy, then chocking it back, will allow you to hold the leach up for a longer period of time. Using less vang will also allow the leach to "stand up", more vang and more downhaul opens it all out. Terms like "stiff" and "wooden" are used when there is too much "wedging" so too much initial straightening of the lower mast. 49er guys use the D1's and get pretty anal about tension, and settings, 1/2 turn so 0.5mm apparently is critical. You want the sail to come off the mast pretty clean, so you need the right amount of camber, and you want it even, a flat exit off the mast and a round leach is very slow. Slightly camber fwd on the beach, because it will suck aft as soon as you get going should be the target. A lot of effort has gone into getting the leach of the jib in exactly the right place, so the main becomes an active extension of "both sails", so don't think about it as a Jib and a Main, think about it as 787 wing with an LE flap deployed. They work together, so when you do something to one, do a suitable adjustment to the other at the same time. Same downwind, you should think about all 3 sails working together. The reason I am stressing this is there is a tendency to jack the mast aft, and fatten up the luff of the lower main, exactly where the jib is exhausting. If your hell bent on that then set your jib further out or slightly ease to give the accelerated air, somewhere to go. jb
  10. JulianB

    Square heads

    Can someone do the Reynolds number comparisons, please? I'm running short of time before I go to China. Jb
  11. JulianB

    Square heads

    When they are not flaring to slowed down, they are pretty pinhead-y to me.
  12. JulianB

    Square heads

    Hi Jim, sorry, I don't think I fully answer you. I think there are square heads and there are exaggerated headboards. The Devoit and the Aero are the latter. For me, the difference is all in the 2 control battens, and their placement, because that is the trigger system by which the square head works. Before anyone says I am sledging the Aero/Devoit, also agree with truncated ellipses, and that's what these are, more so that square heads. Truncated ellipses are particularly good when it comes to centerboards up-range, so the old 18teen #2 and #3 centreboard, where more like an F18 wing than a Peligrin hawk. Maybe they have extended that to a sail. I have never seen a Devoit, and only an Aero without ts sail up at close range (in the real world, sure I have seen them at Alexander Place) so I can't comment. So when Dad and I were following the 49er sailed by Harry (same one) & Simon, early 2000's, what we were impressed by was the triggering of the mast head, it transitioned from power-up mode to de-power mode on demand and effortlessly. The principal control is downhaul, a bit of extra downhaul you bow-string the mast a little more, and it triggers earlier, little less, and it stands up for longer. Anecdotally, we saw that as they where initially sold, sailors use far more downhaul, pulling the headboard cringle out of the sail initially, and then when the FX girls wanted 6:1 downhauls because 4:1 was not enough, the boys said me to, and we started destroying the luff panels just above the cuff from excess load. (yes we have fixed both problems, now its luff tensions in the spinnaker as we have made them flatter and smaller, so the boats are going faster and lower, it never ends) So the sailors have gone from Vang control, which sets up the whole mast as a spring, to downhaul control, which tension the luff of the sail to trigger the masthead. Getting the Euler buckling/crippling load of those top 2 battens right is 90% of the game. You can then opt for high mode/pointing, not much downhaul, lots of leach control and high/slow (relatively, you still doing 10-11knts in a 49er) mode, or max VMG, bit more downhaul, which is getting the head to lay off, and if the boats flat or slightly to windward, that will form an effective end plate, increase AR with all the benefits, boat speed jumps, etc etc etc. The trick is to get the combination of D1 tension right so the downhaul does what you want it to do, on call.
  13. JulianB

    Square heads

    The head length of a 49er mainsail is 743mm, foot length is 2816mm so it 26% approx. I know North like them up around 42% Harry, (my son) tells me the rig on Asko (best performing Aust boat in the last worlds) is great between 9-11knts, very notchy. Problems below that powering up, problems above that with mid leach blowing out (he used a few more expletives) and the head being basically uncontrollable. If they sailed light it was even worse. It's a North rig. We also see this with the FX main. As I have said before when they are good, they are very good, and the trick is to extend the "good" range. Steve, J foils on cats, I guess it is the hull width rule that stops them turning them around (put the J outwards) but I have been watching the Narca's sailing out of MHYC where I beer-can race every Wednesday and your right, they even look wobbly when they get up, with the CoL (foils) moving well inside the CoB (hull) so loss of RM is quite dramatic. We have got some pretty interesting tracking number of the Nacra's, no doubt they will get faster, but max speed in Sopot Poland a few months back in 25-30knts of wind was 28knts. The same day in Arhus, 49er was coming downhill at 26knts in 20knts of wind. Begs the question, when we originally did the 49er we over-killed the laminate, its got about 470gms of glass outside, 300gms inside. Drop that down to GP - 18teen scantlings, 250gms on the outside and 175gms on the inside, stay with S glass (bloody tough) or go Aramid/Carbon, loose that weight plus the weight of the resin, do roll over gunwales, PU cored wings, etc etc, and the weight could drop from 130kgs all up to something under 100kgs (that's a fully rigged/foiled 49er weight, everything but the crew). So do you cut the weight out first, and make it a very different CX49er (can't call it a 49er) or do we go foils [XF49er] (we did 28knts in 18knts of wind, pre the video, with me crewing)? Interesting dilemma. Losing 30kgs of dead weight results in an increase or decrease in live weight. Need to know before you do it, so you can tweak the hull in anticipation. It's impressive to hear the A-class is playing with smaller mast lengths. If its any comfort, with the 18teen, our light air speed was legendary, we would win races by legs in under 7-8 knots with our smaller masts of very similar magnitude, so that should not be an impediment to you. jB
  14. JulianB

    Square heads

    Steve, intrigued by your comment that the A-class is going back Pin-head. I was watching Attenborough's life in cities with Peligrin hawks diving in NYC to catch pigeons. Very pin-head or narrow elliptical tipped wings. And let's face it, these guys (birds) have been at this a lot longer than we have or probably will ever get the opportunity to be at it. So I am going to make a couple of bold statements. #1, if you're going to hang a spinnaker off the top of the mast, you have so much structure up there to do that, it tips the scales towards square heads. i) if you're not going to hang a spinnaker off the top, then the argument is nowhere near as compelling. #2 but our recent tests (in Austria) show that a square head 29er was far more forgiving and far smoother than it's pin-head counterpart. #3 also our recent work here in Aust, with single handers also show far smoother and forgivingness with square heads. i) but the reduction in mast weight between the Alloy and carbon is well over 50% (with the single hander) (29er reduction is far less, 25% max because of all the wires and crap) ii) the CoE position with the square head was about the same as the pin-head & the (carbon) mast ended up being 300mm (1ft) shorter in a 5.2m span. So what I am thinking is this is all about CoL, and sail loading. 49er, 18teen,VOR even a Nacra, no-brainer, moderately low kgs/m² and hanging the spin off the top, scales heavily tilted towards squareheads. 29er, Cherubs, even single handers where the kgs/m² is lowish, ergonomically tilted towards square heads. A-Class, C-class and maybe IC's where the CoL is a lot higher and kgs/m² also higher, pin-heads come back into favour. What would be very interesting is if the A-class sailors opted for non-max length masts (they may have already). When I sailed 18teens, we never had a max length mast, but our sum was different, we were chasing a very defined kgs/m² which was a trigger, maybe we are just too obsessive with length/black bands, etc. Moth's maybe re-inventing the wheel yet again. Again, present Aust 18teen with their obsessive square heads, are a fashion statement and quite absurd!
  15. JulianB

    Square heads

    Again, a tad off topic, but when we did the 49er on foils (www.youtube.com/watch?v=bPPUwvUwEN8) the main lifting foil was an H configuration and we got almost double the CoL that Bora could get with his Moth. So that would suggest the above has some merit.