Hmm...
<br>I got to thinking about this long ago, when I first saw a boarded cat. I assumed guys 'waaay smarter 'n me had tried it, or analyzed it and found it wanting. So I had me another think about why it might not work. What I came up with was along this line:
<br>Let's presume an impossible ideal; you can vary your hull plan and dagger profile and angle-of-attack on the fly to produce optimum lift to windward with the least possible drag - - what would that look like... nevermind how your bows point, the path throu space taken by the sail could only be lower than a certain few degrees off straight upwind. The less drag acting on your boat, the tighter you can sheet. Tight sheeting alligns the force generated by the sail progressively closser to 90 degrees abeam. Therefor it decreases thrust while increasing heeling moment. What's usefull about tight sheeting, is that you can generate force from airflow that is closer to being truely fore-and-aft. When you're really sheeted in hard, pointing up as high as your conventional boarded cat can efficiently sail ( max VMG), the sail is producing less force overall, because it is flat, and less thrust, because the force vector is practically perpendicular to your boards. So drag becomes very significant in limiting your velocity. Two kinds of Drag operate on a high point of sail - hull drag and sail drag.
<br>Since the question seems most directly concerned with hull drag, which is the sum of board drag and hull friction, and board drag must increase with lift, (drag is the coefficient of lift - there being no such thing as a free lunch) clearly the lowest drag, as stated elsewere in this thread, is a symetrical board...
<br>So, I hypothesized way back then... those hi-tech boards must work like... (as also mentioned in this thread) aerodynamic plane wings, (like the ones my fellow RC flyers flew next to my house), getting their lift from angle of attack... It'd be hard to measure, but these long, fine-hulled beauties must point a tiny degree above their real line of travel... albeit a much smaller degree than less 'pointy' cats. That's all leeway is, really, your bow pointing above your net line of true travel.
<br>
<br>Back to pivoting boards, which I never thought of till your fascinating post. (..I got here the long way, I Know! lol) So there's this cat, symetrical boards... pointing slightly above her line of travel... inducing non-linear travel through the water for her hulls, while her boards fall into that low-drag, max lift angle of attack they're shaped for....
<br>I do believe if you allow the boards to cant slighlty, to put them in that angle, while allowing the hulls to go straight through the water, you might reduce hull drag somewhat. The payoff is, when you reduce hull drag, you can flatten the sail more, which reduces sail drag... YES!
<br>
<br>Hmmm....
<br> however, your degree of cant to the boards would have to be proportional to the speed of the cat... I'm guessing you'd want to reduce it as the cat picked up speed, no? So you'd have to build a simple reliable, sand-proof spring linkage to use flow-pressure to induce canting, and you'd naturally want a lock-out for, .... um, for what, anyway? You could engineer it so that both boards would remain parallel to each other, you wouldn't have them fighting each other that way, and if you set your spring-linkage right, the boards would always be canted to produce lift in a manner most likely to allow the bows to point in the boat's true line of travel, so under what conditions would the boards be used where you *wouldn't* want the 'zero-leeway' effect on your cat's hulls? hm....
<br>think
<br>think,
<br>think,
<br>
<br>OKay, linkage designed, looks like this... Say you're sailing on port tack. Both conventional boards experience sideways force, in that they're acting to prevent leeway to starboard. From the 'point of view' of the mounting closets in your hulls, both boards are pressing up to port. So if you used spring loaded felt guides that run vertically up and down just behind the leading edge, one such guide on each side of each rudder, by tuning the strength and elasticity-curve of thes springs, you could allow the leading edges of both boards to move slightly to starboard when on a port tack, and vice versa. You could accomplish the same goal by just allowing your daggerboard trunk to be slightly 'sloppy' in it's forward-end's fit, while being nice 'n precise on the aft edge. it just wouldn't be tunable...
<br>Okay, now for the hull-speed cant-governer. Take the spot where the board's leading edge passes through the deck... when the board is pushed aft by water pressure, this is the point where the structure of the hull resists the dagger's growing inclination to tip over. So, here, you put a tapered wedge that, as higher speeds push the top leeding edge of the board forward into this wedge, it in turn, acts to center the board. You might have to put a spring in here, with a roller guide for the leading edge. Then you just tune this spring to adjust your cant and speed-related transition.
<br>A nice snug fit at all times at the line of contact between the trailing egde and the entire hight of the board closet will keep the board from leaning inboard and outboard during these transitions.
<br>Hey!
<br>In fact, if you do it fine enough, you could just dispense with the felt covered spring loaded guides on the sides of the leading edge... without them, the board is supported and stabilized by: a) contact along the entire in-hull trailling edge, which could be rollers contacting the board just forward of the trailing edge, on both sides, top and bottom, b) the wedge guide at the deck surface of the forward leading edge of the closet. Again, put rollers on this, and put a second wedge just under the first. The top wedge is fixed in place to the hull; the one under it is spring loaded, pushing the board-top aft, when hydropressure allows. As the board top is pushed aft, the clearance to the stationary wedge opens up, allowing the leading edge to cant to windward, in response to the lateral forces it is generating as a reaction to it's primary job of resisting leeway. At the highest speeds, the board-top-leading edge is pushed tightly into the wedge, progressively centering it.
<br>
<br>whadya think?
<br>
<br>Me, I'm worried about the lack of support at the leading edge where the board exits the hull bottom.
<br>
<br>hm...
<br>
<br>
<br>think, think
<br>GOTIT
<br>okay.. rip out those leading edge wedges... keep the trailing edge rollers. now put in two sets of top-and-bottom rollers, one set on each side of the leading edge. Each set is mounted on one piece of stainless, which in turn pivots on a long pin running up and down, just in front of th leading edge of the board. One pin for each side, allowing the top and bottom rollers on that side to move in and out together, but independantly of the rollers on the other side of the board. Stick a tang up from each stainless casting, put a v-roller on each tang, and when the board-top presses hard on these tangs, the stainless castings will turn in, pressing the rollers in, centering the board.
<br>
<br>yes.. much better. the board is now guided at all for 'corners' of its inhull segment, so it'll be, if anything, more stable than conventional boards, it can cant in proportional response to water flow pressure. For weight you've added nine nylon rollers per board, w axles etc, plus those roller pivots,,, hm.. could you make 'em outta carbon? Wonder if the weight cost 'd make up for the drag savings.
<br>
<br>Anybody out there builds one, kindly invite me for a ride! :-)
<br>
<br>Sail Fast,
<br>Ed Norris<br><br>