Loading ...
Sorry, an error occurred while loading the content.

70436Re: Micro with chine runners?

Expand Messages
  • c.ruzer
    Jul 24, 2014
    • 0 Attachment

      Way off track mate. Sea anchors ...running down wind? ...etc etc  cripes such a thing as a sea anchor doesn't need a "belly"... ..car tyres? Bolger even suggested using an anchor in bottomless water to the same end. A plate, a flat sided keel for instance aint got any "belly" .. heard of "lying ahull"? Fore-reaching, ie movement across the wind?



      The "belly" of the sea anchor isn't made so as to "trap" the water to slow downwind progress and keep bow pointed to oncoming seas. A plate would do if it could be rigged, but where would you stow a large rigid plate for the purpose? The "belly" shape is designed in so as to have a thin, flexible, _stowable_ thing made of fabric, let's say canvas, stay deployed in a reliably open configuration so the anchoring due and proportional to the size of its area can work. Would you jump from a plane holding a tarpaulin, extra large bed sheet, or a basic parachute?


      A plate has lift, max cl = 1.  A plate has far less drag when edge on compared to when face on. A plate keel perhaps? Perhaps a chine, or rather the immersed boxboat hull. Now operating above that take a look at the component vectors of the force acting on a sail in a breeze... and see how, and in which direction the boat moves.


      "drag works best when the force is perpendicular to the surface it is acting on." 


      - So how much drag on that hull or plate acts on the side face, and how much on the edge? What is the resultant direction? Yes, purely rhetorical. Include all drag effects if you wish, eg., turbulence, viscous; and those due from each direction too, eg.,  frontal area, edge and wake vortices...


      "you are running down wind, the wind is pretty much perpendicular to the sail.  sailing close hauled, however, there is only enough wind behind the sail (drag) to basicaly keep it's foil shape. barely any drive is drag at that time. the boat is totally lift driven, close hauled." - Running, the apparent wind is much reduced, so of course sail force is also reduced. Close hauled apparent wind speed is higher, there is heaps of side force on the sail, it's where a capsize is more likely! And there is leeway! The small lift component of force acting on the sail is the "drive" acting in an upwind direction that propels the boat forward


      What? Running the slowest point of sail? For many, broad reaching and running are the only points of sail where they have a hope of planning!


      "well, if you sit in your saiboat, on flat water (just to simpify things), perpendicular to a 10kt wind with no sails up, the force of the wind on your hull will be trying to push the boat through the water with the force completely perpendicular to the keel. if you have ever been in such a situation, you will have noticed thatr the wind has no problem doing that at all. in fact, it will push the sailboat just as easily as it woud a row boat without a keel."


      - What? No. Lying ahull the keel will slow the boat slipping sideways downwind. That's the point of lying ahull! That's the point of having a keel in that situation. The boat with the keel will be like a rock compared to your keel-less rowboat skittering rapidly downwind..


      "so, in a situation where drag is at it's greatest, leeway is at it's greatest."


      - Again, what?? The keel boat is still pretty much where it was, and the rowboat without a keel has pretty much disappeared down wind. Get in a sailing dinghy mate, sheet in and try to sail off, now raise the board - what happened? Look, with respect, I'm sorry, but this is a bit too much of a bother to go on with. If you are wedded to the rumint magical thinking that gets around about the mechanism at work behind the functioning of "chine-runners" then you are quite welcome to carry on under the spell.


      "now, hoist sail and catch the wind. as the boat moves forward with greater and greater speed, leeway gets less. the faster the boat is moving the more effective the keel is at stopping leeway.

      "but...wait! when the boat is moving forwards, the force of the water is no longer perpendicular to the keel. in fact, the kee is moving throught the water around 10 degrees away from being paralell to the water moving across it. in other words, drag resisting sideways motion is now very low...but leeway is also very low."

      - Nope. Movement sideways, leeway, is now low compared to movement in the direction the boat is pointing. This is like the old question about two bullets at the same height, one just dropped and the other fired a great distance horizontally from a rifle at the same time - which bullet hits the level ground first?

      "if your theory is right, a sailboat should be rock steady while it is not sailing" Nope, not what I said at all. Wait did I imply it was in frozen water..?

       "the keel can be a lot smaller because water is a lot thicker than air....around 4% of sail area is a good approximation, depending on keel type"


      - Yes. And the faster it goes the smaller it can be too... V^2. ... ( that within a rage of inclination to the oncoming water flow)...  And we're still talking low aspect, not particularly streamlined.


      "an iceberg has tons of mass under the water creating all kinds of drag, but if you stuck a big sail on one it would never sail up wind; only down wind. that's because the underwater surface of an iceberg isn't shaped to create lift. if it was, you could sail one up wind."


      - If it was kinda rectangular or triangular prism like below water, or had such salient projections, then, with large enough sail, it would sail at least as well as an eighteenth century ship...


      "i am not going to argue the point further. believe what you will. plenty of actual info out there on how sailboats work for anyone who wants to know.

      as far as chine runers, as used on paradox...they work very well. i have seen tons of videos of paradoxes sailing close hauled; even one in storm conditions chugging along close hauled where most traditional sailboats would have trouble pointing. there is no doubt they work. i doubt they work better that the micro's keel and switching to them would create a ballast placement issue."

      - You haven't provided an argument. Sorry. Chine-runners... have you seen a Paradox without? It may surprise just how well one still does. PB&F have talked for yonks of their boxboat design "chine sailing" ability in thin water. Heard of the Mersea duck punt or similar? No foils, no keel, no "chine-runners", and no worries up wind! Perhaps you've heard of the Hobie catamaran...


      "adding a small set of well placed and well designed chine runners to the existing set up might help but, it might not."


      - It won't. A fence on the chine will only add wetted area drag. It won't add anything significant to the leeway resistance, lateral resistance, of hull and keel as the keel already supplies way plenty. A "chine-runner" configured as a step, not fence, may have a use in a wet reboarding of Micro but a ladder of some sort or rudder endplate would overall be a far better thing... 

    • Show all 33 messages in this topic