• Announcements

    • Zapata

      Abbreviated rules   07/28/2017

      Underdawg did an excellent job of explaining the rules.  Here's the simplified version: Don't insinuate Pedo.  Warning and or timeout for a first offense.  PermaFlick for any subsequent offenses Don't out members.  See above for penalties.  Caveat:  if you have ever used your own real name or personal information here on the forums since, like, ever - it doesn't count and you are fair game. If you see spam posts, report it to the mods.  We do not hang out in every thread 24/7 If you see any of the above, report it to the mods by hitting the Report button in the offending post.   We do not take action for foul language, off-subject content, or abusive behavior unless it escalates to persistent stalking.  There may be times that we might warn someone or flick someone for something particularly egregious.  There is no standard, we will know it when we see it.  If you continually report things that do not fall into rules #1 or 2 above, you may very well get a timeout yourself for annoying the Mods with repeated whining.  Use your best judgement. Warnings, timeouts, suspensions and flicks are arbitrary and capricious.  Deal with it.  Welcome to anarchy.   If you are a newbie, there are unwritten rules to adhere to.  They will be explained to you soon enough.  

Erwankerauzen

Members
  • Content count

    44
  • Joined

  • Last visited

Community Reputation

1 Neutral

About Erwankerauzen

  • Rank
    Member

Recent Profile Visitors

611 profile views
  1. Foiling Monohull - what would it look like?

    If the leeward foil is canted correctly, it should not be necessary to heel to windward like a Moth. But with windward heel, the CoG of the rig would provide some extra righting moment= extra power.
  2. A Class Worlds - Classic Division

    W&W, Sure Glenn was not sailing A-Cat yet ,but Paper Tiger,. I don't know if Greg Goodall used to make Paper Tiger sails in the 80's 90's? Both were living in Bendigo, and there was water in the lake at these times. Cheers
  3. A Class Worlds - Classic Division

    I should have add. As the stepped leech does not work well downwind, a 45° slope leech in the bottom (below the clew) makes it much better, and I would not be surprised if somebody would add a rubber between the center of the trampoline and the aft /bottom corner of the leech/footsail , in order to meet better the AW twist.
  4. A Class Worlds - Classic Division

    Goodall brother had designed the first A-Cat DS with a wishbone-boom and a stepped leech, just like Pete Melvin at Takapuna. GA has been working with Greg and sailing his boat and sails in the middle 90's This design, if it works well windward as the apparent wind twist is tiny, it is another story Downwind as bottom part of the sail (the stepped part) does not produce significant lift due to too low AoA. You probably remember that ETNZ AC72 was training in New-Zeland at the end of 2012, without DS wing, and as soon as serious things started, all AC72 had closed the gap under their wingsail. So, do you honestly believe that a specialist of A-Cat rig, working as a wing trimmer in a AC Team, always in touch with the best CFD engineers, could have missed such an evolution ? Or do you think he had other priorities ?
  5. A Class Worlds - Classic Division

    SonofaGun, In Bermuda he was not sailing a beach cat. Did Glenn mentionnned you he had decksweeper project on his backburn as soon as 2012 ? But he was a little busy elsewhere to develop a user-friendly DS sail. Fair wind Mate Erwan
  6. A Class Worlds - Classic Division

    Mookiesurf, Pressure gradient will improve the righting moment a little bit. Windward of the sail foot you have hight pressure which push downward on the trampoline if it is airproof Leeward of the sail foot you have a low pressure which sucks up the trampoline, Both create a moment which can be added to the crew righting moment. Right angle endplate are probably not that efficient when settled at the top of the mast, but for DS it is a no brainer whether you consider A-Cat or even F18 where the jib does not take advantage of the tramp's end plate effect. Junctiion drag is not that important, if you know how to compute it do not hesitate, but I think by junction drag could be a kind of "separation drag" as the boundary layer at the corner between tramp and footsail is under double stress and it is likely to separate before the sail leech. But fortunatly with the apparent wind twist (especially downwind) the bottom of the sail experience lower AoA, so less opportunity to see separation.
  7. A Class Worlds - Classic Division

    As far as I remember, I never saw or heard about Glenn capsizing, either with A-Cat or HC Tiger with Darren, So he is a human being after all, that is a good new, I always thought he was an ET
  8. F16 like foiler?

    Thanks Wayne, I will check it Happy Week-End
  9. A Class Worlds - Classic Division

    The lower CoE is an indirect consequence of the DS solution With DS your lift distribution along the span is supposed to vary from elliptical (when you can use the max righting moment, without being overpowered) to triangular (when overpowered), in order to minimize your induced drag. The elliptical area distribution one can observe on new A-Cat DS sails, is just the Apparent wind gradient's consequence, necessary tu put all square feet at full use for downwind leg when apparent wind is lower and hence optimization of the sail plan is more important*. From basic gemotry we know that the center of gravity of an ellipse is at 42% height and a triangular one is at 33% height. Compared to a classic sail, where CoE is probably around 48% height, for sure, there is a loss in righting moment. But.... For similar A-Cat sails (I mean equivalent 2D sections and 2D performance), with a DS sail, the Effective lift coefficient will rise from 0.76 to 0.84, so you have 0.84/0.76=1.11 around +11% extra power, everything else equal. DS sails allow you to have a powerfull section at the bottom of your sail, as it will not be wasted in induced drag vortex. I think the loss in righting moment is more the consequence of the elliptical area distribution than the consequence of DS choice, even if both use to come together as above-mentionned A taller rig might be a solution to address this little disadvantage in light wind. A DS sail with a little less elliptical area distribution and a little more sqared head should be a reasonnable trade-off for non foiling boats which have different requirements like sailing Wild Thing downwind or flying a hull windward as soon as possible.
  10. F16 like foiler?

    Hi, Anybody has an idea on how long is the luff of a F16 spinnaker ?
  11. A Class Worlds - Classic Division

    The lighter the wind, the bigger the lift coefficient of the rig and the bigger the advantage of a DS sail compared to a no DS sail, as induced drag coef is function of Cl^2.
  12. F16 like foiler?

    Sam, I am not sure the VIPER F16 is at the start of its development curve: Before the VIPER, Greg Goodall has successfully designed A-Cat, F18, both of them have been winning machines. That is why, with or without hydrofoils, I feel confident that the VIPER has taken advantage from these successful experiences.
  13. Foiling Monohull - what would it look like?

    Long time ago, the C-Cat serie drop the classic teardrop mast and full batten sail for the wing-sail, not only for aero efficiency, but because the rear beam of the C-Cat was too much stressedby the mainsheet control. Post-Scriptum: the above mentionned assumption of 650 sqm sail area is a bit fantasy as the 28m mast will not provide a reasonnable aspect ratio..So the mast might be longer and the sail area significantly lower, for the same righting moment. The 60 feet width could be put at full use as a lifting surface with windward part at negative AoA and leeward part with a positive AoA, just like an airplane with ailerons= extra righting moment.
  14. Foiling Monohull - what would it look like?

    And in the above mentionned conditions: the driving force of such a rig should be in the 12000N to 15000N
  15. Foiling Monohull - what would it look like?

    Available informations, provide a little data to guess the righting moment and other features under some candid assumptions. Assuming: 1-10 crew members are at 15m from the leeward foil CoE = crew righting moment 2-The CoG of the 5000 kg boat at 6 m from the leeward foil CoE=boat righting moment 20knts apparent wind @ 20° windward a 28 m mast with sailplan's CoE at 42% height max With a sail plan Cl=1 it would required circa: 650 square meter of sail area. You can increase the lift coef by 20% and reduce the sail area accordingly, but it should be in the ball park. The point is which kind of rig with such area is manoeuvrable for match race ?? and the related control systems .. of course