|
a.) no mention is made of a "breaking" wave, and
b.) it an amateur's recollection of an accident. but nice try. stew ped, but nice try anyway. From: (Bryan Glover) Date: 2/8/2005 12:45 A.M. Eastern Standard Time Message-id: Following is from www.seriesdrogue.com and I scoff and mock all you scared weard little guys,like Jax, who will no doubt cry foul, because someone with a commercial interest in this subject dares make a post. Worst Case Breaking Wave Strike I have chosen the case of the Winston Churchill in the 1998 Sydney Hobart race as an example of a worst case breaking wave. The Churchill was a classic wooden sloop of 25 tons displacement and 55 ft. LOA. Of the experienced crew of 9, two perished in the accident. From "Fatal Storm' by Mundle. "A sea came out of nowhere", said Stanley, " I could feel it from where I was in the aft coach house. It picked the boat up and rolled it down its face - 25 tons of boat- into the trough at a 45 degree angle. It was like hitting a brick wall when we hit the bottom". A crewman below reports that a sudden motion of the ship picked him up and threw him 7 ft. He observed that 8 ft of the heavy timber bulwark and planking had been torn off near the leeward shrouds, and the ribs were exposed. . The boat filled rapidly and sank in a matter of minutes. This is an unusual type of accident. Although there are records of many storm casualties, I am aware of no documented instance of a well found yacht of the size and reputation of the Churchill and crewed by an ample group of expert sailors, suffering such catastrophic structural damage that it sank in a matter of minutes. How could this possibly happen? The severity or the storm was extreme but by no means unprecedented. There are numerous reports of large sailing yachts surviving hurricanes of the same general magnitude. Although yachts have been lost in such storms I have been able to find no record of comparable structural damage. History shows that the probability of a yacht being capsized and damaged by a large breaking wave is strongly influenced by the displacement of the vessel. Yachts under 35 ft. have a poor history while yachts over 50 ft are rarely capsized and damaged. The nature and extent of the damage incurred by the Churchill is also most unusual. The vessel was designed by Sparkman and Stevens and was maintained to the highest standard. Yet the heavy timber bulwark was shattered, the planking gone and the ribs exposed. There is no question of the fact that the leeward bow of the boat was driven into solid green water at an extremely high velocity, far higher than would be expected in a simple contact with a breaking wave. We now have a technical understanding of how such a destructive force can be generated. Observations from many experienced sailors on a number of the SH yachts provide data which permit a sound engineering analysis of the performance of the waves and the boats in the race. Water forces are applied to the hull of a yacht by two means, buoyancy forces and dynamic forces. Buoyancy forces are the familiar pressure forces which keep the boat afloat. They never reach sufficient magnitude to damage a well found yacht. Dynamic forces result from the motion of the boat relative to the water, either as a result of the boat velocity or the water velocity due to wave motion. A speeding power boat can be destroyed by striking solid water. Similarly, a sailing yacht can be destroyed if it is accelerated up to a high speed by a breaking wave strike and then impacts solid green water in the preceding trough. This is the fate that befell the Churchill. To understand this phenomenon we must consider the concept of energy. A moving car or boat has energy. This form of energy is called kinetic energy. Kinetic energy is measured in foot-pounds. Kinetic energy can be calculated by the formula KE=1/2 (w/g) times (v squared). Where w is the weight of the car or boat, g is the acceleration of gravity (32.2 ft/sec) and v is the velocity in ft./sec. Thus a 3,000 lb. weight traveling at 30 m |
It would be interesting to get the scantlings of the Churchill to
reconstruct a forensic analysis of the forces that were involved. Without knowing the exact structural schedule, the dissipation of impact is always a 'guess' ... but some value of 'e' between zero and one. It would be fairly easy to back-calculate such values and arrive at least the momentum value. Especially if the boat was constructed to a 'Lloyds scantling rule' the calcs. would be fairly easy. In article , Bryan Glover wrote: Following is from www.seriesdrogue.com and I scoff and mock all you scared weard little guys,like Jax, who will no doubt cry foul, because someone with a commercial interest in this subject dares make a post. Worst Case Breaking Wave Strike I have chosen the case of the Winston Churchill in the 1998 Sydney Hobart race as an example of a worst case breaking wave. The Churchill was a classic wooden sloop of 25 tons displacement and 55 ft. LOA. Of the experienced crew of 9, two perished in the accident. From "Fatal Storm' by Mundle. "A sea came out of nowhere", said Stanley, " I could feel it from where I was in the aft coach house. It picked the boat up and rolled it down its face - 25 tons of boat- into the trough at a 45 degree angle. It was like hitting a brick wall when we hit the bottom". A crewman below reports that a sudden motion of the ship picked him up and threw him 7 ft. He observed that 8 ft of the heavy timber bulwark and planking had been torn off near the leeward shrouds, and the ribs were exposed. . The boat filled rapidly and sank in a matter of minutes. This is an unusual type of accident. Although there are records of many storm casualties, I am aware of no documented instance of a well found yacht of the size and reputation of the Churchill and crewed by an ample group of expert sailors, suffering such catastrophic structural damage that it sank in a matter of minutes. How could this possibly happen? The severity or the storm was extreme but by no means unprecedented. There are numerous reports of large sailing yachts surviving hurricanes of the same general magnitude. Although yachts have been lost in such storms I have been able to find no record of comparable structural damage. History shows that the probability of a yacht being capsized and damaged by a large breaking wave is strongly influenced by the displacement of the vessel. Yachts under 35 ft. have a poor history while yachts over 50 ft are rarely capsized and damaged. The nature and extent of the damage incurred by the Churchill is also most unusual. The vessel was designed by Sparkman and Stevens and was maintained to the highest standard. Yet the heavy timber bulwark was shattered, the planking gone and the ribs exposed. There is no question of the fact that the leeward bow of the boat was driven into solid green water at an extremely high velocity, far higher than would be expected in a simple contact with a breaking wave. We now have a technical understanding of how such a destructive force can be generated. Observations from many experienced sailors on a number of the SH yachts provide data which permit a sound engineering analysis of the performance of the waves and the boats in the race. Water forces are applied to the hull of a yacht by two means, buoyancy forces and dynamic forces. Buoyancy forces are the familiar pressure forces which keep the boat afloat. They never reach sufficient magnitude to damage a well found yacht. Dynamic forces result from the motion of the boat relative to the water, either as a result of the boat velocity or the water velocity due to wave motion. A speeding power boat can be destroyed by striking solid water. Similarly, a sailing yacht can be destroyed if it is accelerated up to a high speed by a breaking wave strike and then impacts solid green water in the preceding trough. This is the fate that befell the Churchill. To understand this phenomenon we must consider the concept of energy. A moving car or boat has energy. This form of energy is called kinetic energy. Kinetic energy is measured in foot-pounds. Kinetic energy can be calculated by the formula KE=1/2 (w/g) times (v squared). Where w is the weight of the car or boat, g is the acceleration of gravity (32.2 ft/sec) and v is the velocity in ft./sec. Thus a 3,000 lb. weight traveling at 30 mph (44 ft./sec.) would have a kinetic energy of 90,000 foot pounds. Now...and this is very important to our understanding of the Churchill disaster...if the moving vehicle strikes an object, the kinetic energy determines the severity of the collision and the extent of the damage. In addition to energy due to motion, a vehicle can possess energy due to height. This type of energy, also measured in foot pounds, is calculated simply as the height times the weight. A 3000 lb car hoisted to a height of 50 ft. would have 150,000 foot pounds of energy. If dropped from 50 ft to a solid surface, the car would dissipate this energy in damage. If the car was compressed by 2 ft. the average force during the impact would be 75,000 pounds. If it landed on its top and compressed four feet (because it was softer) the average force would be 37,500 lbs. .These numbers (compression and force) are not precise but the product must be the same to satisfy the energy balance. more of the same at my site regards Bryan Rich Hampel wrote in message ... What will happen to a 45ft. boat being hit by a 50 ft. wave ...... Not much if the wave isnt steep as the boat will simply lift over the wave. The *steepness* of the wave is important; and, It all depends o n the posiition of the boat vs. the oncoming wave, with being broadside to the wave and steepness of the wave (and whether its breaking or not.) that is thw worst case. Breaking waves (the tops of the waves sliding down the front of the wave in a big 'show' of air filled foam are the 'nasties' that break boats. If the boat is moving, the expertise of the helmsman (able to dodge breaking waves by steering around them, etc. is vitally important as is the 'stability' or sea-worthniness of the boat. A 50 foot wave is no big deal if it isnt a 'steep wave'. An approximate 25-30 ft. wave if steep enough can easily roll a 45ft boat - depends on if its broadside, etc. The inbuilt stabilty is the factor of how a boat survives adverse waves; a lightweight broad beam boat will tend to be vastly more unstable than a heavy, deep, narrow boat ... the lightweight boat having sometimes the advantage of being able to sail away from bad weather faster than a heavy boat. When the sea state is dangerous there are techniques that can be used to survive --- such as using a parachute anchor and holding the bow about 45 degrees to the oncoming waves. The boat will 'slip' slightly backwards and the turbulance of the slip on the surface will cause the waves to 'break' before they hit the boat, etc. Its not the height of the waves but the steepness of the waves and especially if the wave is so steep that the top of wave is 'breaking' that is so dangerous. hope this helps. . net, wrote: I saw the news earlier this week about the 591' ship Explorer with 681 college students on board getting hit by a 50' wave. What will happen if a 45' sailboat gets hit by the same wave ? Does it make a difference which way the boat is facing when it gets hit by a wave this big ? If it does then which way is the best way ? I was told that a good boat can correct itself even if a big wave turns it upside down. So can you just strap yourself to your bed and go to sleep ? Are the windows likely to break and let the water in so that the boat can sink after getting hit many times ? What else do you think can happen ? Thanks for your help. |
Bryan Glover wrote:
.... will no doubt cry foul, because someone with a commercial interest in this subject dares make a post. I dunno, your post does seem too blatantly commercial to me. Worst Case Breaking Wave Strike I have chosen the case of the Winston Churchill in the 1998 Sydney Hobart race as an example of a worst case breaking wave. The Churchill was a classic wooden sloop of 25 tons displacement and 55 ft. LOA. Of the experienced crew of 9, two perished in the accident. From "Fatal Storm' by Mundle. "A sea came out of nowhere", said Stanley, " I could feel it from where I was in the aft coach house. It picked the boat up and rolled it down its face - 25 tons of boat- into the trough at a 45 degree angle. It was like hitting a brick wall when we hit the bottom". A crewman below reports that a sudden motion of the ship picked him up and threw him 7 ft. He observed that 8 ft of the heavy timber bulwark and planking had been torn off near the leeward shrouds, and the ribs were exposed. . The boat filled rapidly and sank in a matter of minutes. This is an unusual type of accident. Although there are records of many storm casualties, I am aware of no documented instance of a well found yacht of the size and reputation of the Churchill and crewed by an ample group of expert sailors, suffering such catastrophic structural damage that it sank in a matter of minutes. How could this possibly happen? A couple of ways, none of them provable. IMHO part of why the Churchill sank was repeated stressing & flexing of the hull, and partial failure of her fastenings. Also that the extreme stress on the rig helped open up the hull as she went down that wave. Once there was any opening at all, the hydraulic force of the water ripped big chunk of planking off. Basically, in these kinds of conditions, the boat is getting dropped on her side every wave. Or partly on her deck. Picture this, picking up your boat 30 feet or more in the air, then tilting it a bit past 90 and dropping it. Bad, eh? Not as bad as doing this same thing for hundreds of reps, interstpersed with having trainloads of water dropped on the boat from height. Considering that Navy cruisers have been sunk in typhoons, and battleships taken severe damage, it's a little much IMHO to expect a small sailboat to withstand anything the ocean can throw. *No* tactics or special gear or design type is going to help. It's a case of simply don't be there when it happens. History shows that the probability of a yacht being capsized and damaged by a large breaking wave is strongly influenced by the displacement of the vessel. Yachts under 35 ft. have a poor history while yachts over 50 ft are rarely capsized and damaged. I think there's more than this factor at work here, although youo're right about bigger = better. Bigger boats are also faster and tend to get less exposure to the extreme conditions, and they are able to take active measures to avoid the worst long after the smaller boats have switched to total survival mode. To understand this phenomenon we must consider the concept of energy. A moving car or boat has energy. This form of energy is called kinetic energy. Kinetic energy is measured in foot-pounds. Kinetic energy can be calculated by the formula KE=1/2 (w/g) times (v squared). Where w is the weight of the car or boat, g is the acceleration of gravity (32.2 ft/sec) and v is the velocity in ft./sec. Thus a 3,000 lb. weight traveling at 30 mph (44 ft./sec.) would have a kinetic energy of 90,000 foot pounds. To put this in perspective, this is roughly equivalent to stopping ten rounds from a .50 cal machine gun. Destructive, nyet? ... Now...and this is very important to our understanding of the Churchill disaster...if the moving vehicle strikes an object, the kinetic energy determines the severity of the collision and the extent of the damage. In addition to energy due to motion, a vehicle can possess energy due to height. This type of energy, also measured in foot pounds, is calculated simply as the height times the weight. A 3000 lb car hoisted to a height of 50 ft. would have 150,000 foot pounds of energy. If dropped from 50 ft to a solid surface, the car would dissipate this energy in damage. If the car was compressed by 2 ft. the average force during the impact would be 75,000 pounds. If it landed on its top and compressed four feet (because it was softer) the average force would be 37,500 lbs. That's not quite right, the force due to deceleration isn't linear. Comparing a braking distance of 2' to 4', the energy is less than half... about a third would be closer... Rich Hampel wrote: It would be interesting to get the scantlings of the Churchill to reconstruct a forensic analysis of the forces that were involved. Without knowing the exact structural schedule, the dissipation of impact is always a 'guess' ... but some value of 'e' between zero and one. It would be fairly easy to back-calculate such values and arrive at least the momentum value. Especially if the boat was constructed to a 'Lloyds scantling rule' the calcs. would be fairly easy. Yes, but it would be impossible to determine exactly how much of the destruction was due to pure force and how much was due to even slightly degraded structural integrity. Hidden rot, bad fastenings, possibly some modification or addition that affected the structure... plank-built wooden boats are really complicated and every single piece is supported by every single other piece. The Churchill was said to be very well maintained and recently rebuilt, but we have no way of knowing her actual, true, material condition at the time of the accident. Personally, I don't think it would matter. As I said earlier, it's my belief that *no* structure built by man can stand up to the ocean at it's worst. Fresh Breezes- Doug King |
Bryan Glover wrote:
.... will no doubt cry foul, because someone with a commercial interest in this subject dares make a post. DSK wrote: I dunno, your post does seem too blatantly commercial to me. CORRECTION: Bryan, I meant to say "Your post does NOT seem too blatantly commercial to me." I apologize for the error, sometimes my fingers type faster than the computer can think. DSK |
This is very true. Although I have never experienced that extreme I was
raised sailing in the caribean. It is all a question of good pumping, semi-sealed boat and a tough crew and you can withstand even a hurricane. The biggest I think ive even been was on 35+knots of wind with seas around 10 feet(Take notice that this is actually from sealine up or down, therefore the waves look over 20 feet tall at times, my father made the slight mistake of not understanding this when reading the pilot charts, and we were a bit shocked for our first 400 mile open sea trip). We were running only on a fully reefed main breaking our maximum speed. Take notice though, this was only on an old Catalina 30(number 112 I think, which is on sale now). But we have raced her and sailed her enough that she could withstand anything we throw at her. "renewontime dot com" wrote in message ... Questions like these have always given me a good chuckle ;-) Anyone that has spent any amount of time at sea or on the waterfront will have plenty of stories that relate to this. I'll spare you from hearing all of my "sea stories"... Having driven one ship in an Atlantic hurricane, another in a Pacific hurricane, a research ship off the coasts of Washington and Oregon during the entire months of November and December (first time I "lost my cookies" in over 30 years at sea), and numerous yachts and ships in gales, I have two bits of wisdom to pass on: 1. Nearly every ship (and most yachts for that matter) can withstand a heck of alot more lousey weather than the crew aboard her can. I know personally of numerous stories of people abandoning their yacht because the weather was just "too bad", only to have their yacht later found completely intact without a bit of damage. 2. If you're on a 45 foot yacht and the weather is severe enough for 50 foot seas... you ain't gonna be sleeping much... ;-) -- Paul =-----------------------------------= renewontime dot com FREE email reminder service for licensed mariners http://www.renewontime.com =-----------------------------------= |
DSK wrote in message ...
To put this in perspective, this is roughly equivalent to stopping ten rounds from a .50 cal machine gun. Destructive, nyet? Your analogy is extremely misleading, since the area to which this force would be applied is hundreds of times smaller. This leads to hull-pressures that are hundreds of times larger That's not quite right, the force due to deceleration isn't linear. Comparing a braking distance of 2' to 4', the energy is less than half... about a third would be closer... Thats just plain wrong, the force (which is what Jordan was talking about) due to decelaration IS linear with breaking distance (given a certain initial velocity). The formula for force due to a constant deceleration (in terms of initial velocity and 'breaking distance') is: F = m*v^2/(2d) |
Bryan Glover wrote:
Your analogy is extremely misleading It may be misleading, but I dunno about "extremely misleading." ... since the area to which this force would be applied is hundreds of times smaller. This leads to hull-pressures that are hundreds of times larger A large part of that is also due to the energy transient. In any event, my point was to not underestimate the destructive power of the ocean, which certain types of cruisers are always doing. That's not quite right, the force due to deceleration isn't linear. Comparing a braking distance of 2' to 4', the energy is less than half... about a third would be closer... Thats just plain wrong Well, working with a not-infallible memory, it happens sometimes. I will go back to the old textbook and see what it says. DSK |
|
On Tue, 8 Feb 2005 16:16:24 UTC, DSK wrote:
structural damage that it sank in a matter of minutes. How could this possibly happen? A couple of ways, none of them provable. IMHO part of why the Churchill sank was repeated stressing & flexing of the hull, and partial failure of her fastenings. The boat had recently been refastened etc. Which makes one wonder whether it was done right... Considering that Navy cruisers have been sunk in typhoons, and battleships taken severe damage, it's a little much IMHO to expect a small sailboat to withstand anything the ocean can throw. *No* tactics or special gear or design type is going to help. It's a case of simply don't be there when it happens. Except that a reasonable proportion of the fleet did manage to sail through the same conditions and make it to the other end (not counting all tose who prudently retired from the race), so obviously some things did help. Chris |
| All times are GMT +1. The time now is 04:39 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004 - 2014 BoatBanter.com