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#11
posted to rec.boats.cruising
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Urgent ! Can anyone understand these safety data ?
Evan Gatehouse wrote: Gary wrote: I think the stability curves are wrong. If you plug the numbers into the formulas at US sailing you get a much higher AVS. 110 degrees just doesn't make sense. Not only that but the 460's keel, although seemingly a little light, is bulbous with the weight quite low. Something is wrong with that graph. Gaz I didn't find the formula at US Sailing's site but...How do you find AVS without using a sophisticated stability program that knows the shape of the hull? The US Sailing formula may give an indication of ultimate stability (the capsize screening formula) but that is a very simple rule of thumb. The inclining experiment data, which does determine the VCG of the real boat, is plugged into a stability program (GHS/Autohydro etc.) that gives the stability curve. Robert has retired fairly recently but he should be able to help you with your questions. Evan Gatehouse Thank you very much for your help. The dealer said he was going to call Robert Harris for me regarding my concern. If his design isn't as bad as the report suggests he'll probably be happy to explain to me why I shouldn't worry too much about the stability of this boat. |
#12
posted to rec.boats.cruising
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Urgent ! Can anyone understand these safety data ?
Evan Gatehouse wrote:
Gary wrote: I think the stability curves are wrong. If you plug the numbers into the formulas at US sailing you get a much higher AVS. 110 degrees just doesn't make sense. Not only that but the 460's keel, although seemingly a little light, is bulbous with the weight quite low. Something is wrong with that graph. Gaz I didn't find the formula at US Sailing's site but...How do you find AVS without using a sophisticated stability program that knows the shape of the hull? The US Sailing formula may give an indication of ultimate stability (the capsize screening formula) but that is a very simple rule of thumb. The inclining experiment data, which does determine the VCG of the real boat, is plugged into a stability program (GHS/Autohydro etc.) that gives the stability curve. Robert has retired fairly recently but he should be able to help you with your questions. Evan Gatehouse Try he http://www.sailingusa.info/keelboat.htm Under sailing calculators in the right find angle of vanishing stability. The problem with the inclining data is that it only takes hull shape and weight distribution into account. It doesn't allow for things like pilothouses or foam filled masts. I still think the curve is wrong and Tayanas claim of an AVS of 0 is probably correct. |
#13
posted to rec.boats.cruising
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Urgent ! Can anyone understand these safety data ?
Gary wrote:
Evan Gatehouse wrote: Gary wrote: I think the stability curves are wrong. If you plug the numbers into the formulas at US sailing you get a much higher AVS. 110 degrees just doesn't make sense. Not only that but the 460's keel, although seemingly a little light, is bulbous with the weight quite low. Something is wrong with that graph. Gaz I didn't find the formula at US Sailing's site but...How do you find AVS without using a sophisticated stability program that knows the shape of the hull? The US Sailing formula may give an indication of ultimate stability (the capsize screening formula) but that is a very simple rule of thumb. The inclining experiment data, which does determine the VCG of the real boat, is plugged into a stability program (GHS/Autohydro etc.) that gives the stability curve. Robert has retired fairly recently but he should be able to help you with your questions. Evan Gatehouse Try he http://www.sailingusa.info/keelboat.htm Under sailing calculators in the right find angle of vanishing stability. The problem with the inclining data is that it only takes hull shape and weight distribution into account. It doesn't allow for things like pilothouses or foam filled masts. I still think the curve is wrong and Tayanas claim of an AVS of 0 is probably correct. O.k. I'm a polite guy on usenet but you sir are totally wrong and beginning to **** me off. I'm a naval architect. I do this stuff for a living. The stupid calculator only is used to give an ESTIMATE of the AVS. An inclining experiment establishes the VCG of the boat in a real world test. It does NOT calculate the AVS. For that you need software that does take into account the shape of the hull and the pilothouse. GHS and Autohydro DO that! You could model a foam filled mast as part of the model if you wished. They are far more trustworthy and are accepted by USCG for stability calculations of commercail vessels Here's the formula from US Sailings site. Note that in the last line, the formula says the AVS = 110 + ..... This says that the AVS is ALWAYS going to be = 110. There are lots of boats that are 110! From US Sailings web site: " This formula gives an estimate of the angle of vanishing stability or the angle the boat can heel and still right itself. This formula does not fully take into account the vertical position of the center of gravity (VCG)." Screening Stability Value ( SSV ) = ( Beam 2 ) / ( BR * HD * DV 1/3 ) BR: Ballast Ratio ( Keel Weight / Total Weight ) HD: Hull Draft DV: The Displacement Volume in cubic meters. DV is entered as pounds of displacement on the webpage and converted to cubic meters by the formula: Displacement Volume in Cubic Meters = ( Weight in Pounds / 64 )*0.0283168 The Beam and Hull Draft in this formula are in meters. These values are entered in feet on the webpage and are converted to meters before SSV calculation. Angle of Vanishing Stability approximately equals 110 + ( 400 / (SSV-10) ) |
#14
posted to rec.boats.cruising
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Urgent ! Can anyone understand these safety data ?
Evan Gatehouse wrote:
Gary wrote: Evan Gatehouse wrote: Gary wrote: I think the stability curves are wrong. If you plug the numbers into the formulas at US sailing you get a much higher AVS. 110 degrees just doesn't make sense. Not only that but the 460's keel, although seemingly a little light, is bulbous with the weight quite low. Something is wrong with that graph. Gaz I didn't find the formula at US Sailing's site but...How do you find AVS without using a sophisticated stability program that knows the shape of the hull? The US Sailing formula may give an indication of ultimate stability (the capsize screening formula) but that is a very simple rule of thumb. The inclining experiment data, which does determine the VCG of the real boat, is plugged into a stability program (GHS/Autohydro etc.) that gives the stability curve. Robert has retired fairly recently but he should be able to help you with your questions. Evan Gatehouse Try he http://www.sailingusa.info/keelboat.htm Under sailing calculators in the right find angle of vanishing stability. The problem with the inclining data is that it only takes hull shape and weight distribution into account. It doesn't allow for things like pilothouses or foam filled masts. I still think the curve is wrong and Tayanas claim of an AVS of 0 is probably correct. O.k. I'm a polite guy on usenet but you sir are totally wrong and beginning to **** me off. I'm a naval architect. I do this stuff for a living. The stupid calculator only is used to give an ESTIMATE of the AVS. An inclining experiment establishes the VCG of the boat in a real world test. It does NOT calculate the AVS. For that you need software that does take into account the shape of the hull and the pilothouse. GHS and Autohydro DO that! You could model a foam filled mast as part of the model if you wished. They are far more trustworthy and are accepted by USCG for stability calculations of commercail vessels Here's the formula from US Sailings site. Note that in the last line, the formula says the AVS = 110 + ..... This says that the AVS is ALWAYS going to be = 110. There are lots of boats that are 110! From US Sailings web site: " This formula gives an estimate of the angle of vanishing stability or the angle the boat can heel and still right itself. This formula does not fully take into account the vertical position of the center of gravity (VCG)." Screening Stability Value ( SSV ) = ( Beam 2 ) / ( BR * HD * DV 1/3 ) BR: Ballast Ratio ( Keel Weight / Total Weight ) HD: Hull Draft DV: The Displacement Volume in cubic meters. DV is entered as pounds of displacement on the webpage and converted to cubic meters by the formula: Displacement Volume in Cubic Meters = ( Weight in Pounds / 64 )*0.0283168 The Beam and Hull Draft in this formula are in meters. These values are entered in feet on the webpage and are converted to meters before SSV calculation. Angle of Vanishing Stability approximately equals 110 + ( 400 / (SSV-10) ) Glad I'm getting to you Nav Arch. You do seem to have a grasp on the above formulae but fail to explain why the boat has an AVS of 110 in the graph and yet the designer and builder both claim it has a much greater AVS. In fact the extremely high AVS of the Tayana Vancouver 460 is discussed in many places around the net. There is no way the AVS is 110. If you really are a Nav Arch and do this for a living, then do it for us. Work out the numbers using your program and the data available and give us your results (which are still only an estimate). As a Nav Arch it should only take you a couple minutes. Right???? You also earlier said : "- the ballast/displacement ratio is overly low, meaning a tender boat with not enough stability " A Nav Arch would know that initial stability is more than lots of ballast. A raft has no ballast and is not tender. Wouldn't you say that you are jumping to conclusions by not taking into account hull form and the location of the ballast? In other articles on the net, they also talk of the boat as "stiff" and "stands up to her sails well". Your turn. Gaz |
#15
posted to rec.boats.cruising
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Urgent ! Can anyone understand these safety data ?
Gary wrote:
Evan Gatehouse wrote: Gary wrote: Evan Gatehouse wrote: Gary wrote: I think the stability curves are wrong. If you plug the numbers into the formulas at US sailing you get a much higher AVS. 110 degrees just doesn't make sense. Not only that but the 460's keel, although seemingly a little light, is bulbous with the weight quite low. Something is wrong with that graph. Gaz O.k. I'm a polite guy on usenet but you sir are totally wrong and beginning to **** me off. I'm a naval architect. I do this stuff for a living. The stupid calculator only is used to give an ESTIMATE of the AVS. An inclining experiment establishes the VCG of the boat in a real world test. It does NOT calculate the AVS. For that you need software that does take into account the shape of the hull and the pilothouse. GHS and Autohydro DO that! You could model a foam filled mast as part of the model if you wished. They are far more trustworthy and are accepted by USCG for stability calculations of commercail vessels Gary wrote Glad I'm getting to you Nav Arch. You do seem to have a grasp on the above formulae but fail to explain why the boat has an AVS of 110 in the graph and yet the designer and builder both claim it has a much greater AVS. In fact the extremely high AVS of the Tayana Vancouver 460 is discussed in many places around the net. There is no way the AVS is 110. If you really are a Nav Arch and do this for a living, then do it for us. Work out the numbers using your program and the data available and give us your results (which are still only an estimate). As a Nav Arch it should only take you a couple minutes. Right???? You also earlier said : "- the ballast/displacement ratio is overly low, meaning a tender boat with not enough stability " A Nav Arch would know that initial stability is more than lots of ballast. A raft has no ballast and is not tender. Wouldn't you say that you are jumping to conclusions by not taking into account hull form and the location of the ballast? In other articles on the net, they also talk of the boat as "stiff" and "stands up to her sails well". Your turn. Gaz Okay, my turn again. I just googled you and see you may be a Nav Arch. So why don't you calculate the AVS? I am quite confident (and I am not a Nav Arch) that the boat will have a better stability curve than is represented by the one posted. If it doesn't, and it has an AVS of 110, I wouldn't touch it for anything but coastal wandering. It will surprise me because the AVS claims for the 460 are 0 degrees on all the Tayana websites and the other Harris boats are so seaworthy. Really though, since we are not doing the buying, this is just an interesting discussion. No need to get ****ed off. Gary |
#16
posted to rec.boats.cruising
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Urgent ! Can anyone understand these safety data ?
Gary wrote: Okay, my turn again. I just googled you and see you may be a Nav Arch. So why don't you calculate the AVS? I am quite confident (and I am not a Nav Arch) that the boat will have a better stability curve than is represented by the one posted. If it doesn't, and it has an AVS of 110, I wouldn't touch it for anything but coastal wandering. It will surprise me because the AVS claims for the 460 are 0 degrees on all the Tayana websites and the other Harris boats are so seaworthy. Really though, since we are not doing the buying, this is just an interesting discussion. No need to get ****ed off. The report including the curve was sent to me by Tayana's engineer named Basil last Sunday (Monday in Taiwan). "Nice to talk with you. Re AVS of Vancouver 460 is 110 degrees. ... Enclosed the report of inclining experiment total 3 pages. The last page shown the GZ curve. Please let me know if you have more questions." The AVS was probably determined from the curve but I don't know if they actually closed all the hatches and turned the boat upside down for the inclining experiment :-) BTW, didn't somebody recommend a Catalina (with an AVS of 105) over this Tayana and the Beneteaus for crossing the Pacific ? |
#17
posted to rec.boats.cruising
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Urgent ! Can anyone understand these safety data ?
I've got this report from Tayana for the Vancouver 460 Pilot but don't know how good it is. http://tayana46.tripod.com/safety.htm I have another idea. Since this boat has a 325-gallon fuel tank and a 240-gallon water tank and the inclining experiment was done with all tanks half full, would I be able to significantly improve on the stability if I fill up all the tanks for my offshore cruising ? I can install a watermaker and solar panels so I won't have to draw too much water and fuel from these tanks. |
#18
posted to rec.boats.cruising
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Urgent ! Can anyone understand these safety data ?
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#20
posted to rec.boats.cruising
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Urgent ! Can anyone understand these safety data ?
Gary wrote:
Okay, my turn again. I just googled you and see you may be a Nav Arch. I've met Mr. Gatehouse and he is indeed a Naval Architect and a good one. So why don't you calculate the AVS? Because (as he's been trying to tell you) it requires more data. I am quite confident (and I am not a Nav Arch) that the boat will have a better stability curve than is represented by the one posted. Based on what? Your gut feeling? If it doesn't, and it has an AVS of 110, I wouldn't touch it for anything but coastal wandering. Now here I agree. An LPOS (or AVS or whatever the TLA de jour is) of 110 is far too low for any kind of rough weather sailing even near coasts. Going back a little bit You also earlier said : "- the ballast/displacement ratio is overly low, meaning a tender boat with not enough stability " A Nav Arch would know that initial stability is more than lots of ballast. Right, in fact the B/D ratio has little effect on *initial* stability. But notice that in the original sentence, the word "stability" was used, not the phrase "initial stability". A boat can have very high initial stability and great sail carrying power, but a very low LPOS (think scows or catamarans). A very different type of boat can have low initial stability and lots of ballast for lots of *reserve* stability... ie steeply increasing righting moment at higher angles of heel. A lot of old fashioned narrow heavy boats are said to "heel only so far, and then stiffen up like a rock." A boat like this can sail well at higher angles of heel if the hull shape is fair & the rig/rudder are balanced well. It can also have a very high LPOS yet be very unsearthy.... think of the Twelve Meters. ... A raft has no ballast and is not tender. Wouldn't you say that you are jumping to conclusions by not taking into account hull form and the location of the ballast? Umm, no... from the discussion so far, I'd say that you are the one doing exactly that. In other articles on the net, they also talk of the boat as "stiff" and "stands up to her sails well". That can easily be a function of her SA/D ratio as much as hull form & ballast. Fresh Breezes- Doug King |
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