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12 Whiner

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  1. Yeah, I was quoted 5K to get a NA to sign off on my 30'er. That seemed like a "I don't want to do it" price to me but I didn't exactly shop around after
  2. Spoonie

    everybody doin' it?

    Have all the maxis with booms up had black decks? There has to be some sort of "thermal lift" effect there surely
  3. Spoonie

    everybody doin' it?

    Yeah, but there are a lot of easily driven hulls out there, especially upwind below hull speed. As per my comment above, I'm not sure it is limited to such boats but the effects might be more pronounced. Small amounts of lift probably makes a big impact if you've stripped all the drag out of your rig too. The north etchells tuning guide has the boom 40mm above center in light winds with a straight, if not hooked leach. If those are real world numbers then it's pretty subtle. Even the 72 above is pretty subtle... I tried looking at the Ac cat wings but perspective is everything. I can get mine 100mm - 150mm or so above centre with the top batten just flicking open (late 90's IMS 30'er). That seems to be pretty quick for me up to about 8-10 on flat water. I trim the jib full if not hooked with the leads in hard. I pretty much discovered it by accident one day but didn't think anything of it as being weird. *shrug* someone would have run it through a computer and backed it up with trials I'm sure
  4. Spoonie

    everybody doin' it?

    Well you also have to consider the rig package as a hole has it moves through the air as well and not just the entry and exit flows. If you look at the angle of the boom on those maxis, if they're crabbing side wise that badly that it's now on center line, I'd be very surprised. Mind you, the angles on some are less extreme: but that's still what, 5 or 6 degrees at least? Do they really have that much leeway? The shadow helps you follow the curves though. Trace the jib flow out, around, and past the leach of the main. The only thing that matters is the lift & drag the whole rig package generates relative to the boat. Does the rig create more or less lift in this configuration? does it create more or less drag? if you can increase lift with the same or less drag then win! The big programs might be able to get away with it more than pleb boats because they've stripped so much other drag out of the rig through sail, mast, rig, that they can suffer a little more from the trim for extra lift and still get forward drive. I don't know. IMHO it's kinda like the discussion on overhangs. Overhangs have to be doing work for them to be effective otherwise it's just surface drag. how much work is your leach doing? could it be doing more or are you just dragging it through the air?
  5. Spoonie

    everybody doin' it?

    More sigh... I was going to walk away but I can't help myself here. I'm going to start by saying y'all should watch this video from 1938 (yes 1938) Now yes it is a solid wing of an airplane and well sails on booms are not solid wings on air planes but well... whatever. Back to the link I posted earlier, there's a really nice visual in the last picture: Basically what happens here is as the AoA of the trailing flap increases, the flow starts to bifurcate and whip around the front of the foil. If there was no foil in front, then as it whips around with higher velocity, it would probably separate and you just get a bucket load of drag as the video above shows. But there is a foil in front so the front foil helps to keep the flow attached over the back of the back foil. if that slot wasn't there and it was one continuous foil, then you probably also get separation (i.e turbulence and drag) That point of bifurcation on each foil is the point of highest pressure on that foil. So by having this series of flaps and slots, you can increase the pressure under the wing, with increased flow attachment on the top, higher AOA, more lift, and less drag. There is a point where this stops working and that's where you can no longer maintain attached flow across the outside of the wing. So what about boats? On a yacht, the jib acts as that leading foil helping to keep the flow attached to the back of the main. As long as you can keep flow attached to the back, you can in theory keep winding that main to windward. In doing so, you move the high pressure point further aft in the sail and further accelerate the flow across the back of the main as flow bifurcates from the front of the main and around the front of the mast. An interesting experiment would be to put a whole bunch of tell tales around the front of the main and mast about 1/2 m above the boom and see if you can see the contra flow around the front of the mast. Now as you go towards the hounds, the jib gets progressively smaller relative to the main so the main acts more and more like a cat rigged boat. Cat rigged boats, without a slotted flap on them somewhere, don't like high AoA without a lot of drag, and so without twist, the mid and top of the sail will start to stall. Overlap vs Non-Overlap To me, this is no-brainer for boats with non-overlapping jibs in light to moderate airs. As long as you can keep the flow across the back of the main going. Overlapping rigs it should still work I would think but you'd have to get the trim right on both sails, and I think it would look more like this: Some benefit, but not as much as having the slot there. Bathtubs vs Rocketships To me, for any easily driven hull form, old or new, upwind this is a no brainer in light to moderate and flat waters. I think the challenge here will be maintaining flow. You need to maintain flow over both your keel and rig packages. A lightweight boat in sloppy water may struggle. An old long, heavier boat with a big chorded keel may actually fair better. I don't know. Slow fat bathtubs I'm not so sure but should probably still work in flatter water I would think. If the boat pounds to a stop then that's a different story, you need to reattach flow to everything. IMHO that's where the slow bathtubs will suffer In Short This is not about trading height for speed, it's about milking that extra few % out of your rig package albeit within a very small groove. You don't get height by simply pointing in that direction, you get height by buying it with flow over your rig and keel (ie. speed). boom to windward helps give you that bit of extra camber out of your rig in the bottom 1/3rd as a whole package giving you more lift with roughly the same drag profile (as long as you keep flow attached). It stops working when either the breeze picks up, you can no longer keep flow attached, or you become overpowered and you need to drop the boom down. As to lazy helmsmen, well, if the helmsman has to work then you are doing something wrong. Yachts work because a balance of forces. If you are fighting against those forces then you are putting the handbrake on somewhere. Upwind you want to create a neutral to semi positive feel to the helm. Boom angle is one of the tools at your disposal for doing that. Use it or not, I don't care.... And finally... If you want to argue I'm wrong, go fire up Java Foil, Sail7 or similar and run some simulations. I guarantee you that's what the big programs have done. Theory is nice and all as well, so back it up with some practical on the water testing. Again guarantee that's what the big programs have done. Will it work for your boat? I don't know, but I can certainly tell you why it *should* work and where it may not Cheers Craig
  6. Spoonie

    everybody doin' it?

    Sigh... OK well, whatever...
  7. Spoonie

    everybody doin' it?

    Should still work. The pics shown here are of dragons in moderate to heavy air. Both pictures they are depowering the rig
  8. Spoonie

    everybody doin' it?

    Nothing wrong with the physics, the scenario and your description linking back to cat rigged boats is completely irrelevant. "winged sail" it says in the description. Ie solid. Go find some flow diagrams of slotted wings EDIT: here are some nice ones. http://cfd2012.com/types-of-flaps.html
  9. Spoonie

    everybody doin' it?

    I think the Ed isn't paying much attention either. The last discussion included everything from etchells to ior bathtubs.
  10. Spoonie

    everybody doin' it?

    See previous discussion on this topic. Think flaps down on a jumbo. High lift, high drag... Close hauled the sail plan works as one foil. It's useless thinking about the main trim on its own. It's even more useless showing some vector diagram of an asymmetric solid sail without slots. I would imagine would work fine for pretty much any boat that is relatively easily driven up wind. Fat slow block of flats maybe need not apply
  11. Spoonie

    Removing Duct Tape Residue From Cabin Top

    Eucalyptus oil
  12. Most clubs in Sydney exclusively use this system, Maybe they use a measurements based one on the side (ams,orc,irc etc...)
  13. Spoonie

    Smart/Not Smart - booms above centerline

    It's very simple. Think flaps down in an aircraft. High lift, high drag, high aoa. There is a point drag exceeds lift and you go slower. Either because wind is stronger or aoa is too high. Work your tell tales appropriately. Keep your head out of the boat with one eye on the knot meter.
  14. Spoonie

    Want to do a new design 30 square meter build

    In any of these similar types of rules, the trend was towards longer and heavier. IMHO, light air speed is more a function of wetted surface area and that having a bit of momentum in light air was a good thing. But I don't design or build yachts for a living. The rule itself contains fairly detailed scantlings as well. I did a lot of googling and link following to get all the bits I found. It's hard because I'm searching in English. Once I found some leads, I could start refining the search. The German association has race results and reports. I'm sure the swedes do to. Worth looking at both the 30's and 22's. Seems like more active development in the 22's and one or two new builds a year. Lots of new builds seem to be older designs. An interesting point is many of the 22's are as big as the 30's
  15. Spoonie

    Want to do a new design 30 square meter build

    Juan k, Botin, carkeek have apparently all done recent meter boats. Different rule but I imagine some similar concepts. And that is beyond the guys like Bob and fastyacht in this thread.