dht@druri.UUCP (Davis Tucker) (12/11/85)
>With that rig, anything closer hauled than a broad reach is out of the question >Even a beam reach would be impossible, so you might have a bit of difficulty >going anywhere except exactly where the wind blows (i.e. running). If you have >ever run a spinnaker, you know that without some rigid support (spinnaker or >whisker pole) it is extremely hard to control the sail, poleless spinnakers >notwithstanding. A rigid solid pole with masthead rig shouldn't be that >difficult to build, if you are worried about biulding a mast. > >Earle A. Sugar Tell that to the ten or fifteen guys who race kite-propelled craft every year at Portsmouth Speed Week. Kite rigs have their problems, surely, but the problems do not include an inability to sail close to the wind; in fact, kites can sail even closer to the wind than anything except a solid wing, because they can be articulated and flattened very easily, using the wind's force to accomplish this, along with guy wires and other control mechanisms. For all their faults, kites offer an incredible potential in control of the wind, as every surface element can (conceivably) be manipulated to its maximum potential. The standard method for speed trial racing of kite craft (the same method for many craft) is to start off on a broad or beam reach and build up speed, maintaining a straight course from start to finish as the apparent wind quickly builds up to close-hauled. As the wind swings abeam and ahead, the kite is canted up and *forward* of the boat, still to leeward, however. The kite is manipulated with some kind of control structure which allows the sailor to control its three-dimensional position in relation to the wind and the boat so as to maximize lift and minimize drag, similar in many respects to the instinctive way that a boardsailor cants his sail and mast as the wind grows stronger and moves forward. It really is of no importance whether a fully-articulated rig, such as a sailboard, is attached at its base to the craft or to a guy wire up in the air. What matters is that the sail, or kite, is anchored in some way to allow the transmission of kinetic energy to the craft itself. In a conventional boat, this anchor point is the mast step and shrouds. In a sailboard, this point is the freely-rotating mast step. In a kite craft, this point is where the guy wire or wires connect to the boat. Kites offer one great advantage over mast rigs - they totally negate heeling force. All and any heeling force that might be directed at a regular rig is translated into upward lift, which literally picks the boat up out of the water, reducing wetted surface, etc. Also, and this may be what gets kite craft into the running, kites are sailing far above the water, where the wind is much stronger, and thus have much more kinetic energy at their disposal, none of which will be translated into heeling moment (although the drag of the guy wires will negate the lift at some point). Unfortunately, kite rigs do not handle gusty conditions very well, nor heavy chop, nor quick changes of apparent wind, nor (obviously) light air conditions. They are also far too complicated, which causes frequent breakdowns. Far more promise is evident in venturi sails, solid wings, and fully-articulating rigs. Davis Tucker
cwg@uiucdcsp.CS.UIUC.EDU (12/12/85)
Although a kite-powered boat can sail close-hauled with respect to the current wind, how close can it sail with respect to the true wind? In other words, can such a boat be designed to make much speed up wind compared to conventional sailboats? For a while I have been sketching on a plan for a "sail boat" that puts everything but the keel (center board?) up with the kite--in other words, a hang-glider connected to a "keel" by (probably two) guy wires. Looks like it will need high winds, great for slicing up stink pots, but a pain to get back to base when the wind drops. Anybody looked at such designs?