Posted on Saturday, September 02, 2017 - 11:59 pm:
The sail is a wing, not just a sack that the wind blows. This is why it's possible to sail into the wind. Not directly into the wind, but within a few degrees.
Although I've never been sailing, it's appealing and I've watched hundreds of youtube videos. But from what I understand, sailing close hauled or close reach is slower than running with the wind. So the sail being a wing doesn't explain (to me) how the vessel can sail faster than the wind speed.
I assume it has something to do with hydrofoil shapes.... once the boat starts moving and the underwater "foils" lift the boat and minimize water resistance... that's about the end of my understanding.
In the video I posted, near the end a guy says that the America's Cup vessels, if placed in the Amazon river with no wind, facing upstream, would move upstream at double the rate of the river current. I just don't get it. I can see how enough current would obviously lift the bulk of the vessel out of the water. But current making a vessel move upstream? I'm lost.
Anytime a sail is moving, it creates it's own wind. Sailing across the wind, known a a beam reach, you have the full measured wind speed, along with the speed of the boat creating more wind that the sail sees. The faster the boat, the more wind the sail sees. As you pick up speed, you can bear off to a broad reach, where you are going a bit down wind. Now you are also going the direction the wind wants to push you. This tends to be a faster point of sail, but you also see less wind in the sail as you are going with the wind. Boat speed keeps the sail powered up though. It's a funny thing, as small changes in actual wind speed can make huge changes in lift provided by the sail. A small drop in wind can actually have the sail backwinded. Also, any power harnessed by the sail has to be offset by foil(s) in the water. For speed sailing, you try to keep these foils to a minimum to reduce the drag they produce. On a broad reach, you don't need as much foil in the water, and at high speed you don't need as much. I noticed in the first video I posted, they had the ability to retract the rudder when they got up to speed. Makes a lot of sense. Then you use the hull as an airfoil that provides lift, to reduce the amount of hull in the water. That also reduces drag. Hydrofoils can be used to both provide horizontal lift to counter the wind in the sail, and lift the hull out of the water. The boat in the video I posted is built to only go on a broad reach, and only in one direction. It virtually can't turn around and go back the other direction.
Going up wind is a matter of getting enough lift from the foils in the water to push you upwind more than the wind pushes everything above the water down wind.
I've had the experience of getting the wind under the board on a windsurfer, and lifting off the water, much like what happened in the second video I posted. Broke a rib once when that happened.
Remember...the sail is a wing. The wind isn't blowing the sail like its a piece of plywood. The sail generates lift in the same way that an airplane wing generates lift. It is the lift that pushes the boat.
I was going to buy an International Moth foil boat. But found I didn't have local winds that would let me keep in practice enough and I'm too heavy for optimum performance. Pity. They look like a lot of fun.
Neat. Why don't we have more pleasure boats with deployable hydrofoils? So much more efficient. No wake for water skiing would be nice for slalom skiers.
I've had the idea for a little two person foil conversion of a small boat for years. The expensive part is the extension of the outboard engine and jet drive lower unit. The foils I'd just lay up myself out of carbon fiber and vacuum infuse.
I just could never justify the cost when I count how many times I've been boating the last century.
Much easier to justify a motor glider.
(Message edited by aesquire on September 04, 2017)
Posted on Wednesday, September 06, 2017 - 10:54 pm:
Local Craiglist ad here in Indiana.
Urinal in Refrigerator
Functional urinal mounted inside a hollowed out refrigerator. Light inside comes on when doors opened. Currently not hooked up to plumbing or electric. Perfect for garage, barn or man cave. Free to whoever wants to move it from my garage.
Posted on Thursday, September 07, 2017 - 10:03 pm:
I understand the kites. 82 or 83 I built a 12 foot delta in england. It picked me up and slammed me. 36 square feet lifts fast. I had a 30 square foot parafoil that got me in 98 or 99. Not as bad. It snapped the 250 pound line I was flying it with. The delta had stronger line on it. I like kites but I'm not very good at balancing on a board.