fireball
Well-Known Member
But with the windward hull in the water there is some water providing upward thrust on the hull (hence it will float!) whereas if it is just clear of the water then there is no upward thrust and just downward force ...
Hanse Review
- Thread starter arni
- Start date
ex-Gladys
Well-Known Member
Actually the "weight" in those circs has to be less, because the hull is floating and supported by water. In "dinghy" cats the perceived maximum performance position is as I described previously, then you get max centreboard effect from windward hull as well.
Sailfree
Well-Known Member
Stand corrected you are right - if I remember my history correctly that bloke Archemedies caused the romans some difficulties as well!
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moondancer
Well-Known Member
[ QUOTE ]
And to the other contributor who dismisses AVS as 'just one factor', it is a very important factor in ultimate safety. Of course, its only in very severe conditions that it will have any relevance, but ask those in the Fastnet disaster how important it was.
[/ QUOTE ]
I may come across as being pedantic here but I think you are wrong and in danger of making people focus on the wrong issues regarding safety. The fastnet incident was unique to its time in that boats with very low stability had evolved as the IOR handicap rule favoured boats with low stability. It also highlighted dozens of issues on safety that are now incorporated into general practice.
The following is quoted from the US Sailing Association and gives a very good insight into stability and boat length.
"A longer boat is desirable in heavy weather and high waves. No matter how big a sinusoidal wave is, it should not capsize a boat. A breaking wave is a different story, these waves have a slope of 70 degrees and if higher than a boat is long, the boat cannot go over them. An extreme breaking wave hitting the boat's stern or bow may cause it to tumble over end on end (pitchpole or pitchpoling). If a breaking wave hits the boat on the beam, it can more easily broach or capsize the boat. Thus, one of the most important factors in surviving high waves is the length of the boat.
A high stability is most important when hit beam-on with a breaking wave and may only give a relatively small advantage.
Boat "stability" or resistance to being capsized is most important when a boat is hit beam-on with a breaking wave. Boats with a wider beam are less stable that those with a narrow beam. However, boats with a wider beam are stiffer (heel less) and have more living room below.
According to Andrew Claughton in Heavy Weather Sailing 30th ed. p 21 "This (the test data presented in the chapter) suggests that alterations in form (of a sailboat) that improves capsize resistance may be rendered ineffective by a relatively small increase in breaking wave height."
If a boat is positioned into a breaking wave, most boats (wide and narrow beamed) can survive a 55% LOA (overall boat length) breaking wave. However, a 35% LOA breaking wave hitting a wide-beamed boat beam-on can easily capsize the boat. All yachts tested rolled to 130 degrees. No yacht, no matter how stable, could consistently resist capsizing when hit, beam-on, with a 55% LOA breaking wave. (K. Adlard Coles' and Peter Bruce's (editors) Adlard Coles' Heavy Weather Sailing (30th edition) Stability of Yachts in large breaking waves. Chapter 2 pp11-23 International marine, Camden, Maine)
Putting this in perspective in a 40 foot (LOA) sailboat: In a highly stable boat wave survivability would increase by 8 feet, if hit beam-on by a breaking wave. A 40 foot sailboat no matter how stable will not consistently survive a 22 foot breaking wave. Thus, in a strong gale with 22 foot seas and breaking waves, a 40 foot sailboat is at risk of capsizing no matter how stable.
Most important factor is an experienced crew: Of all the factors, it is far more beneficial to have an experienced crew that can either avoid or position the boat into large breaking waves.
The 1998 Sydney - Hobart race was one of the worst sailing disasters in recent maritime history. And from it many lessons were learned regarding the functioning of boats and crews in heavy weather. 115 boats left Sydney and were hit by an unexpected typhoon. Seven boats were abandon and five were lost. The 1998 Sydney to Hobart Race Review Committee report, summarized by Peter Bush, committee chair, reported the following as one of the significant findings: "There is no evidence that any particular style or design of boat fared better or worse in the conditions. The age of yacht, age of design, construction method, construction material, high or low stability, heavy or light displacement, or rig type were not determining factors. Whether or not a yacht was hit by an extreme wave was a matter of chance." (Ref: Rob Mundle in Fatal Storm, Publisher's Afterward p 249. International Marine/McGraw-Hill Camden, Maine.) "
I feel a very balanced assessment.
If you look at the Sydney - Hobart which is the best documented disaster involving extreme weather the AVS of a boat made no difference to the outcome. One of the heaviest most traditional boats in the race, the Winston Churchill (which was in the first Sydney - Hobart race) tragically sunk having hit the bottom of a massive trough. Boats that were hit by a large breaking wave were rolled and damaged. Those that by chance missed were not.
IMHO Length matters, downflooding angles matter a lot, AVS a small bit and the crew matter the most.
A friend of mine has just come back from the 2007 AZAB in a Jeanneau JOD 35. This, I think, has an AVS of 109 degrees. He bought the JOD after being terrified in a Yachting Monthly Triangle race in a well known UK lifting keel bought known for its high ballast ratio. He feels far safer in the JOD.
And to the other contributor who dismisses AVS as 'just one factor', it is a very important factor in ultimate safety. Of course, its only in very severe conditions that it will have any relevance, but ask those in the Fastnet disaster how important it was.
[/ QUOTE ]
I may come across as being pedantic here but I think you are wrong and in danger of making people focus on the wrong issues regarding safety. The fastnet incident was unique to its time in that boats with very low stability had evolved as the IOR handicap rule favoured boats with low stability. It also highlighted dozens of issues on safety that are now incorporated into general practice.
The following is quoted from the US Sailing Association and gives a very good insight into stability and boat length.
"A longer boat is desirable in heavy weather and high waves. No matter how big a sinusoidal wave is, it should not capsize a boat. A breaking wave is a different story, these waves have a slope of 70 degrees and if higher than a boat is long, the boat cannot go over them. An extreme breaking wave hitting the boat's stern or bow may cause it to tumble over end on end (pitchpole or pitchpoling). If a breaking wave hits the boat on the beam, it can more easily broach or capsize the boat. Thus, one of the most important factors in surviving high waves is the length of the boat.
A high stability is most important when hit beam-on with a breaking wave and may only give a relatively small advantage.
Boat "stability" or resistance to being capsized is most important when a boat is hit beam-on with a breaking wave. Boats with a wider beam are less stable that those with a narrow beam. However, boats with a wider beam are stiffer (heel less) and have more living room below.
According to Andrew Claughton in Heavy Weather Sailing 30th ed. p 21 "This (the test data presented in the chapter) suggests that alterations in form (of a sailboat) that improves capsize resistance may be rendered ineffective by a relatively small increase in breaking wave height."
If a boat is positioned into a breaking wave, most boats (wide and narrow beamed) can survive a 55% LOA (overall boat length) breaking wave. However, a 35% LOA breaking wave hitting a wide-beamed boat beam-on can easily capsize the boat. All yachts tested rolled to 130 degrees. No yacht, no matter how stable, could consistently resist capsizing when hit, beam-on, with a 55% LOA breaking wave. (K. Adlard Coles' and Peter Bruce's (editors) Adlard Coles' Heavy Weather Sailing (30th edition) Stability of Yachts in large breaking waves. Chapter 2 pp11-23 International marine, Camden, Maine)
Putting this in perspective in a 40 foot (LOA) sailboat: In a highly stable boat wave survivability would increase by 8 feet, if hit beam-on by a breaking wave. A 40 foot sailboat no matter how stable will not consistently survive a 22 foot breaking wave. Thus, in a strong gale with 22 foot seas and breaking waves, a 40 foot sailboat is at risk of capsizing no matter how stable.
Most important factor is an experienced crew: Of all the factors, it is far more beneficial to have an experienced crew that can either avoid or position the boat into large breaking waves.
The 1998 Sydney - Hobart race was one of the worst sailing disasters in recent maritime history. And from it many lessons were learned regarding the functioning of boats and crews in heavy weather. 115 boats left Sydney and were hit by an unexpected typhoon. Seven boats were abandon and five were lost. The 1998 Sydney to Hobart Race Review Committee report, summarized by Peter Bush, committee chair, reported the following as one of the significant findings: "There is no evidence that any particular style or design of boat fared better or worse in the conditions. The age of yacht, age of design, construction method, construction material, high or low stability, heavy or light displacement, or rig type were not determining factors. Whether or not a yacht was hit by an extreme wave was a matter of chance." (Ref: Rob Mundle in Fatal Storm, Publisher's Afterward p 249. International Marine/McGraw-Hill Camden, Maine.) "
I feel a very balanced assessment.
If you look at the Sydney - Hobart which is the best documented disaster involving extreme weather the AVS of a boat made no difference to the outcome. One of the heaviest most traditional boats in the race, the Winston Churchill (which was in the first Sydney - Hobart race) tragically sunk having hit the bottom of a massive trough. Boats that were hit by a large breaking wave were rolled and damaged. Those that by chance missed were not.
IMHO Length matters, downflooding angles matter a lot, AVS a small bit and the crew matter the most.
A friend of mine has just come back from the 2007 AZAB in a Jeanneau JOD 35. This, I think, has an AVS of 109 degrees. He bought the JOD after being terrified in a Yachting Monthly Triangle race in a well known UK lifting keel bought known for its high ballast ratio. He feels far safer in the JOD.