Erwankerauzen

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About Erwankerauzen

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  1. Erwankerauzen

    Sailing anywhere between Perpignan and Montpelier

    Be carefull with your stuffs, your car, anything on the boat trailer, and so on.... This part of south of France is the "Thief Coast" a bit like in Italy, everybody will try to steal your stuff It is not a special treatment for foreigners, it is the same for frenchies coming from the north of the country. Avoid "Etang de Ber" which is in the middle of the oil reffineries and has been holding for decades the gold medal of the most polluted area in France. Happy Holidays Erwan
  2. Erwankerauzen

    Foiling Monohull - what would it look like?

    Hi, These last few days, I have been traveleing to the sea, and noticed similar features on Hydrofoils from very different machines 1-A big all white Oman trimaran in Lorient harbour 2-A foiling windsurf 3-An A-Cat Exploder All of them seem to share common features: 1-A sharp leading edge 2-A maximum thickness which seems a little aft 3-A Concave shape on both sides of the last 35% of the wing section leading to very low exit angle. Main Difference: The bigger the boat the larger the camber and thickness (for structural reasons I guess). We still have to wait to see what kind of foils the new AC boat will carry, in the meantime that a few infos to chew for the addicts. Cheers
  3. Erwankerauzen

    Moth decksweeper and lowered mast stumps

    PhilS, The 5.70 m luff is an assumption regarding a new rig trade-off regardless of the rule box. But your remark prompts me to crunch the figures again with a 5.185 max luff lenght, in order to compare apples with apples. So with a full decksweeping foot sail with a 5.185 luff lenght and a 8.25 m^2 we have: Oswald coefficient =2 So we should have the following results: Aspect Ratio = 6.52 2D Lift Coefficient = 0.91 (for a 0.70 3D lift coef as above-mentionned) Induced drag coef = 0.0404% Induced drag = 20.33 Newtons (apparent wind @ 10 m/s) So even in this case, the decrease for induced drag remains significant relative to the classic rig: 20 Newtons vs 46 Newtons. Wish you a nice week Cheers Erwan
  4. Erwankerauzen

    Moth decksweeper and lowered mast stumps

    Thanks Phil, Doug, Connor & Inebriated for taking time to post. I was travelling last week, and I am not confortable writing from a smartphone, that is why I waited to be back home to post. "Poor reasonning" Is almost a compliment as it was more or less intuitive, and based on former A-Cat induced drag calculations. As most of you are engineers, I will try to post a few calculations to illustrate the intuition: Of course it is purely theorical and the ability to tack or gybe in 1 second as can be seen on Youtube, is not considered . Classic Moth Rig Theorical DeckSweeper Rig Sail Area 8.25 m^2 8.25 m^2 Luff lenght 5.185 m 5.70 m Gap(% luff lenght) 10% 0% Oswald Coef 1.19 2 Geometric AR 3.26 3.94 Effective AR 3.88 7.87 For 10m/s Apparent wind velocity and a 350 Newtons actual sail lift, we should have Cl(3d) 0.70 0.70 Cl(2d) equivalent 1.06 0.79 Cxi (Induced drag coef) 0.092% 0.0253% Induced Drag 46.3 Newtons 12.73 Newtons Detla= 33.5 Newtons Main assumption : both rigs have the same height for their center of effort. The 33.5 Newtons Induced Drag difference is interesting to consider relative to the total driving force created by these rigs. With Apparent wind angle around 20° relative to the boat: The driving force is around F= 350 Newtons * Sin (20°) = 119 Newtons. Of course it is a bit meaningless as it is not possible to have both: a full decksweeping sail and the possibility to tack or gybe under the footsail. If the crew moves his weight aft, in order to go behind the leech for tack or gybe, I dont believe it is possible according to the relative weight of the crew vs total boat displacement. But, because the performance "carrot" if even larger than for A-Cat, I feel confident a smart Aussie or Kiwi will bring a breakthrough sooner or later. Best regards Erwan
  5. Erwankerauzen

    Moth decksweeper and lowered mast stumps

    Thanks Teknologica, In other words an actual breakthrough cannot happen in the Moth Class due to the rule box. So I feel confident a smart guy will create a new rig/platform which will use the standard Moth foils and will outperform the Moth at cheaper price, but of course, nothing will be compliant with the Moth rule box. It will be another serie. Happy week end Erwan
  6. Erwankerauzen

    Moth decksweeper and lowered mast stumps

    Thanks Mika, Nice Moth champion interviews :
  7. Erwankerauzen

    Moth decksweeper and lowered mast stumps

    Thank you Tecknologica for taking time to answer my candid post. Regarding the loss of power, it should be interesting to guess if it is a consequence of a lower rig or a less powerfull sail ? Decksweeping sails for A-Cat, not only have a lower induced drag, but everything else equal they are likely to deliver more hp, as the bottom is more efficient. And if you have an elliptical lift distribution (with an elliptical area distribution like today's A-Cat sails) your sail CoE is at 42% height when trimmed for max power. Of course, the above statements work well for decksweeping sails with 0 gap. Decreasing gap is better, but as some gap still remains, improvements are probably less obvious and could be offset by other effects. This development class is amazing and I feel confident it will remain so for a long time. Thanks again for posting Tecknologica and fair winds. Erwan
  8. Any conferences proceedings or video of the presentations to published ???
  9. Erwankerauzen

    Moth decksweeper and lowered mast stumps

    As I am not a Mothie, I hesitate to post, but I if my remarks can trigger some comments: 1-Windward, for me it is a no brainer, whether the foot sail is straight+ canted downward or stepped the narrower the gap, the less the induced drag, especially in the lights winds when you are looking for hp in your sail. 2-Downwind, with more twist in the apparent wind, if your leech is stepped, the stepped part is loosing some AoA according to the apparent wind, so the bottom corner of the leech could find an advantage to be pulled toward the middle of the boat with a rubber or similar. In other words, the shorter the chord going down the leech, the more the leech need to be pulled toward the middle of the boat. In conclusion as long as the bottom part of the sail is put at full use downwind, the new boom/sail arrangements should outperform the older ones both upwind and downwind. Or at least upwind in any cases. That is a rookie bet, so be indulgent Mates. Cheers
  10. Erwankerauzen

    AC36 CLASS RULE

    Any interesting details regarding the "soft main wingsail" ??
  11. Erwankerauzen

    Moth decksweeper and lowered mast stumps

    Thanks a lot Mika for these accurate measurements. Cheers Erwan
  12. Erwankerauzen

    Moth decksweeper and lowered mast stumps

    Thanks a lot Punchy & Tinga Happy week end & fair winds
  13. Erwankerauzen

    Moth decksweeper and lowered mast stumps

    Sorry if the question looks stupid as I am not a Moothie: I saw on Moth's measurement rules that the mast lenght is 6.25 meters. On forum I see sail luffs are around 5.185 meters and masts a little longer I guess ? So I don't know where is the difference 6.25 - 5.185 = 1.0625 meter Or is 6.25 meters a maximum mast leght and today's 5.185 meters mast is a result of an optimization for the foiler mode? I would love to know actual mast lenght for last decksweeper sails. Thanks in advance Erwan
  14. Erwankerauzen

    Moth Foiler & Back bone issue

    Thank You Everybody for your contribution, So far I have been sailing only Cat, and especially non-foiler A-Cats. Trapezing doesn't create problem with my back so far, but I am afraid to take risk with my knees trapezing on foils with footstrap. That is why I exploring something different. My back bone problem is L1-S1. I resume swimming 2000 meters every 3 days to get good global fit before to address abs seriously as suggested by 17Mika Team-GBR PhilS among other Fair Winds to all Cheers Erwan Post Scriptum: The potential of aero improvement of the Moth rig makes it is also very attractive, for recreational CFD.