This whole long discussion on tippy sailing got me started thinking about my experience with what was actually a knock down rather than just "tippy sailing". As I said in an earlier post, I had an American 17. (Actually, she is still for sale - anyone want one?) It was a classic mistake and I did not have much experience. We were running with the wind in conditions that were too much for full sails. We came about to close-hauled. The momentum of the boat stopped, a big gust hit us, and we went down. So far, down that I could look through the cabin windows from the cockpit, they were under water, and water was pouring into the cockpit. I released all the sails and eventually the boat came up. Since then I have made some assumptions about the physics of what happened. It seems to me that when a boat is stopped, it is more susceptible to a knock down. But that means that forward motion increases stability. Is that right? Also, it seemed to me that the bow of the boat was trying to dive to the bottom of the lake. It felt like we were about to pitch pole this small mono hulled boat from a dead stop. From that, I assumed that there is a forward and downward vector that will push the bow of the boat down when it is tipped so far that the rail is under water. But now I am wondering if that is right or if I was just imagining it. Does anyone have any comments? - Just trying to understand the physics of sailing. Thanks, Bill Leathen
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Inverted air foil
Bill, I think you are probably right about your experience. Under normal sail, there is a forward 'vector' making the boat advance. As you heel, the direction of those forward/leeward forces must rotate toward an upside down wing, and 'lift'(in the form of horizontal movement across the surface)becomes 'dive'. Why heeling seems more intense when forward motion is absent is harder to describe. Probably to do with the single channel (heel) for the wind energy.
Bill, I think you are probably right about your experience. Under normal sail, there is a forward 'vector' making the boat advance. As you heel, the direction of those forward/leeward forces must rotate toward an upside down wing, and 'lift'(in the form of horizontal movement across the surface)becomes 'dive'. Why heeling seems more intense when forward motion is absent is harder to describe. Probably to do with the single channel (heel) for the wind energy.
You must have b r o a c h e d , but...
not all parts of the puzzle do fit yet. You wrote: "We were running with the wind in conditions that were too much for full sails. We came about to close-hauled. The momentum of the boat stopped, a big gust hit us, and we went down" I doubt that you truly "came about" or even became "close-hauled" in the classical sense of these terms. However, you clearly rounded up suddenly and violently into the wind. The million-dollar questions are: (1) did that happen spontaneously or did the helmsman initiate that turn (?); (2) if a turn was initiated, where was it attempted (i.e. while going over the top of a wave, surfing down the back of one or being in the trough between two waves)(?); and (3) what were wave and wind conditions like (?). Either way you could be right in that you may have come close to pitchpoling. Fortunately, however, you "only" ended up broaching instead. I promise to try and explain what may have happened in more detail if you are able to provide the missing links. Flying Dutchman
not all parts of the puzzle do fit yet. You wrote: "We were running with the wind in conditions that were too much for full sails. We came about to close-hauled. The momentum of the boat stopped, a big gust hit us, and we went down" I doubt that you truly "came about" or even became "close-hauled" in the classical sense of these terms. However, you clearly rounded up suddenly and violently into the wind. The million-dollar questions are: (1) did that happen spontaneously or did the helmsman initiate that turn (?); (2) if a turn was initiated, where was it attempted (i.e. while going over the top of a wave, surfing down the back of one or being in the trough between two waves)(?); and (3) what were wave and wind conditions like (?). Either way you could be right in that you may have come close to pitchpoling. Fortunately, however, you "only" ended up broaching instead. I promise to try and explain what may have happened in more detail if you are able to provide the missing links. Flying Dutchman
About the same thing
happened to me early in my sailing career. I had built a 16' planing hull daysailer in night hobby class (2 years worth of wood work and laying fiberglass) and it was the afternoon of the first day I had it out. That morning she had handled nicely in light winds. The wind slowly increased through the day, and when we went out after lunch it was blowing 5 to 8 knots. My wife and I took her out for a pleasant afternoon sail, and after about an hour when we made the turn for home the wind was blowing about 15 or more knots. The boat surged forward and began to feel almost out of control - I remember the rudder feeling almost "mushy." I know now that the boat was planing, but at that time it just felt like we were riding the back of a runaway rodeo bull and had very little input as to what it might choose to do next. I didn't even know enough to raise the daggerboard - it was all the way down. My greatest fear at the time was pitchpoling, so we both sat pretty far back. We continued this exhilerating but spooky ride for about a mile and a half with the wind dead aft until we came to the inlet where the boat was to be kept. My plan was to sheet the main in gradually as we approached where we needed to turn, then make the turn (left) and simultaneously free the mainsheet to spill much of the force on it as we came onto a reach. I still think it would have worked, but as we started the turn I saw the boom wasn't swinging out even though the mainsheet was uncleated. Too late I noticed the sheet was wrapped and fouled around the swivelling cleat. Over we went as the wind hit our tightly sheeted mainsail, tripping over the daggerboard. I tried to right the boat by standing on the end of the board, but she turned turtle as the mast filled with water. No longer did we wonder what to name her - later that week "Flipper" was painted upside down on her transom, and she rewarded me with many hours of sailing pleasure in the next two years, until her untimely demise in a hurricane. I believe your observation implies that with the boat nearly stopped and the main sheeted about fore-and-aft there is a large sideways vector component and not much of a forward one. This results in a strong heeling force. Non-planing boats often tend to "settle" lower in the water up front as the apparent wind increases. Perhaps these are the effects you observed.
happened to me early in my sailing career. I had built a 16' planing hull daysailer in night hobby class (2 years worth of wood work and laying fiberglass) and it was the afternoon of the first day I had it out. That morning she had handled nicely in light winds. The wind slowly increased through the day, and when we went out after lunch it was blowing 5 to 8 knots. My wife and I took her out for a pleasant afternoon sail, and after about an hour when we made the turn for home the wind was blowing about 15 or more knots. The boat surged forward and began to feel almost out of control - I remember the rudder feeling almost "mushy." I know now that the boat was planing, but at that time it just felt like we were riding the back of a runaway rodeo bull and had very little input as to what it might choose to do next. I didn't even know enough to raise the daggerboard - it was all the way down. My greatest fear at the time was pitchpoling, so we both sat pretty far back. We continued this exhilerating but spooky ride for about a mile and a half with the wind dead aft until we came to the inlet where the boat was to be kept. My plan was to sheet the main in gradually as we approached where we needed to turn, then make the turn (left) and simultaneously free the mainsheet to spill much of the force on it as we came onto a reach. I still think it would have worked, but as we started the turn I saw the boom wasn't swinging out even though the mainsheet was uncleated. Too late I noticed the sheet was wrapped and fouled around the swivelling cleat. Over we went as the wind hit our tightly sheeted mainsail, tripping over the daggerboard. I tried to right the boat by standing on the end of the board, but she turned turtle as the mast filled with water. No longer did we wonder what to name her - later that week "Flipper" was painted upside down on her transom, and she rewarded me with many hours of sailing pleasure in the next two years, until her untimely demise in a hurricane. I believe your observation implies that with the boat nearly stopped and the main sheeted about fore-and-aft there is a large sideways vector component and not much of a forward one. This results in a strong heeling force. Non-planing boats often tend to "settle" lower in the water up front as the apparent wind increases. Perhaps these are the effects you observed.
interesting physics
Bill- I gotta agree with you that being stationary would aggravate the heeling situation. For one thing, it wouldn't immediately produce a weather helm effect (which under the circumstances would help a moving, overpowered boat in close hauled orientation- due to hull shape, mostly). The resulting roundup would naturally luff the sails and right the hull. A combination of being motionless and having a "stalled" set of sails, where wind is more perpendicular to the sails than parallel, would produce pretty nasty conditions, but not normally something that would happen without a windshift and puff happening simultaneously. The other condition that I find more distressing, in terms of knockdowns and broaches, is reaching downwind, perhaps with too much sail aloft, and having few options for depowering the main since it is already flush with the spreaders. It can be pretty sporty, but actually more stable, in a dead run since the boat sits flatter. Just don't go to sleep. Interesting questions!
Bill- I gotta agree with you that being stationary would aggravate the heeling situation. For one thing, it wouldn't immediately produce a weather helm effect (which under the circumstances would help a moving, overpowered boat in close hauled orientation- due to hull shape, mostly). The resulting roundup would naturally luff the sails and right the hull. A combination of being motionless and having a "stalled" set of sails, where wind is more perpendicular to the sails than parallel, would produce pretty nasty conditions, but not normally something that would happen without a windshift and puff happening simultaneously. The other condition that I find more distressing, in terms of knockdowns and broaches, is reaching downwind, perhaps with too much sail aloft, and having few options for depowering the main since it is already flush with the spreaders. It can be pretty sporty, but actually more stable, in a dead run since the boat sits flatter. Just don't go to sleep. Interesting questions!
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