What about changing tacks?
Asymmetrical spinnakers are generally jibed, not tacked. Start with sail fully loaded. Bear off slowly, easing
the sheet as smooth and fast as you can without collapsing the sail. The trick is to use the sheet pressure to get
the sail out in front of the boat. If you don't get the sail eased out before the boat gets downwind, it will collapse
and fall into the headstay. As the boat passes through dead downwind, release the old sheet completely and take
up on the new sheet. The sail is jibed outside and in front of the headstay. If you have a long enough bowsprit,
and it is blowing pretty hard, you may want to try jibing inside the tack downhaul. No matter which system you
use, turn from a broad reach to a broad reach. Do not stop in the middle of the turn, or you will encourage the
sail to get wrapped around the headstay. The lighter the air, the higher the reaching angle you will need to sail,
both at the outset, and as you exit the jibe. In very light air, you may have to physically help the sail around the
headstay.
Thursday, 28 April 2011
Tuesday, 5 April 2011
Digital Selective Calling
Digital Selective Calling
Jan 27,2010 00:00 by infomar
Digital Selective Calling is the fundamental reason why the GMDSS system is different from what has been available until now. Prior to DSC, most radio calls were initiated by making a voice call to the desired station, and relying on somebody at that station hearing the call and then responding to it. All too often the sheer volume of calls made this an impossible task. On a summer afternoon in popular sailing areas it was not unusual for there to be over 400 calls per hour on VHF channel 16. At best, this made it very tedious, and often impossible, to hear calls meant for you, or more importantly, for anybody to hear a distress call. Clearly, something had to be done.
Initially a partial answer was found by shifting some of the calling traffic off channel 16. In some areas Coast Stations stopped monitoring channel 16 and listened for calls only on their working channels. Similarly, calls to marinas were stopped on 16 and moved to other designated channels. That relieved some of the pressure, but now there was no single channel that everybody was listening to, so vessels missed calls meant for them and distress calls sometimes went unheeded.
On board commercial ships, the problem was even worse. They were not only expected to monitor channel 16, but also 13 for bridge-to-bridge calls, 2182 MHz on MF, and if on the high seas, one or more HF distress frequencies. What a headache - literally! The salvation lay in DSC. The DSC control unit monitors all the required frequencies, and lets the operator know when there is a call for his station, or when there is a distress or other urgent call. Best of all, it does all this in total silence. No longer are we subjected to the continuous cacophony on channel 16 nor the static crashes and bangs on 2182 MHz. Instead, we wait for the phone to ring, as it were.
How DSC Works
How is this miracle achieved? The DSC control unit is somewhat like a pager which alerts the receiving station that there is traffic waiting for them. The name, Digital Selective Calling, goes a long way to explaining how it works.
DSC uses a Digital signal to send a message, via the sending station's radio, to alert the receiver that there is traffic for them, and to tell them where and how to receive the traffic. This DSC message is termed a DSC Call, or sometimes a DSC Alert. The digital message includes several pieces of information which will be displayed on the receiving station's DSC control unit:
1. The Maritime Mobile Service Identity of the sending station. The MMSI is a nine digit number, and it is the DSC equivalent to the call sign, or the 'phone number' of a station. It is issued as part of the GMDSS station licence.
2. The MMSI of the station being called. This can be an individual vessel or Coast Station, a specific group of vessels, or in the case of distress, urgency or safety traffic, to all stations.
3. The priority of the call - distress, urgency, safety or routine. DSC can be used for setting up any type of call, from a Mayday to making a phone call home.
4. For distress calls, the DSC alert can include the nature of the distress, e.g. fire, sinking, explosion, pirate attack etc.
5. For distress calls the position of the vessel is normally included. If the control unit is interfaced to a Global Positioning System receiver, then the position will be added automatically. If there is no GPS receiver connected to it, then the position, and the time that the position was valid, must be keyed in.
6. The requested working frequency and mode of transmission for the traffic. The DSC is only used to set up the call; the actual communication is conducted on another radio channel - distress or working channel as the case may be - and it can be conducted in either voice or telex mode, depending on circumstances.
DSC calls are Selective, because as we have seen above, they can be directed to a selected station or stations. Previously virtually all calls were received by all stations who were in range of the transmission. However, the DSC control unit looks at each call that it receives and determines if the call is addressed to it specifically, to it as part of a group, to all stations, or to vessels in the area where the receiving station is located. When such a call is received then the operator is alerted, usually by a buzzer and an indication on the screen. The information as to where and how the traffic will be sent is displayed on the screen. All other calls are simply ignored.
The last part of the name sums up what DSC is about. It is used for calling another station to advise them that there is traffic for them, and to what channel or frequency they should tune their radio to receive this traffic. When a DSC call is transmitted by VHF, it is sent in F1B modulation, at a speed of 1,200 baud. At this speed, all the data in a DSC Alert can be transmitted in about half a second. On MF/HF things happen just a little slower. The modulation is J2B and the speed of transmission is 100 baud. This results in a DSC Alert on MF or HF taking between 6 and 7 seconds to be transmitted. The DSC control unit transmits the DSC calls through the ship's VHF and/or MF/HF radio. Although installations and equipment obviously vary, the control unit is normally also connected to a dedicated receiver which monitors the DSC frequencies for incoming DSC calls, regardless of to which frequencies the ship's radios are tuned.
Jan 27,2010 00:00 by infomar
Digital Selective Calling is the fundamental reason why the GMDSS system is different from what has been available until now. Prior to DSC, most radio calls were initiated by making a voice call to the desired station, and relying on somebody at that station hearing the call and then responding to it. All too often the sheer volume of calls made this an impossible task. On a summer afternoon in popular sailing areas it was not unusual for there to be over 400 calls per hour on VHF channel 16. At best, this made it very tedious, and often impossible, to hear calls meant for you, or more importantly, for anybody to hear a distress call. Clearly, something had to be done.
Initially a partial answer was found by shifting some of the calling traffic off channel 16. In some areas Coast Stations stopped monitoring channel 16 and listened for calls only on their working channels. Similarly, calls to marinas were stopped on 16 and moved to other designated channels. That relieved some of the pressure, but now there was no single channel that everybody was listening to, so vessels missed calls meant for them and distress calls sometimes went unheeded.
On board commercial ships, the problem was even worse. They were not only expected to monitor channel 16, but also 13 for bridge-to-bridge calls, 2182 MHz on MF, and if on the high seas, one or more HF distress frequencies. What a headache - literally! The salvation lay in DSC. The DSC control unit monitors all the required frequencies, and lets the operator know when there is a call for his station, or when there is a distress or other urgent call. Best of all, it does all this in total silence. No longer are we subjected to the continuous cacophony on channel 16 nor the static crashes and bangs on 2182 MHz. Instead, we wait for the phone to ring, as it were.
How DSC Works
How is this miracle achieved? The DSC control unit is somewhat like a pager which alerts the receiving station that there is traffic waiting for them. The name, Digital Selective Calling, goes a long way to explaining how it works.
DSC uses a Digital signal to send a message, via the sending station's radio, to alert the receiver that there is traffic for them, and to tell them where and how to receive the traffic. This DSC message is termed a DSC Call, or sometimes a DSC Alert. The digital message includes several pieces of information which will be displayed on the receiving station's DSC control unit:
1. The Maritime Mobile Service Identity of the sending station. The MMSI is a nine digit number, and it is the DSC equivalent to the call sign, or the 'phone number' of a station. It is issued as part of the GMDSS station licence.
2. The MMSI of the station being called. This can be an individual vessel or Coast Station, a specific group of vessels, or in the case of distress, urgency or safety traffic, to all stations.
3. The priority of the call - distress, urgency, safety or routine. DSC can be used for setting up any type of call, from a Mayday to making a phone call home.
4. For distress calls, the DSC alert can include the nature of the distress, e.g. fire, sinking, explosion, pirate attack etc.
5. For distress calls the position of the vessel is normally included. If the control unit is interfaced to a Global Positioning System receiver, then the position will be added automatically. If there is no GPS receiver connected to it, then the position, and the time that the position was valid, must be keyed in.
6. The requested working frequency and mode of transmission for the traffic. The DSC is only used to set up the call; the actual communication is conducted on another radio channel - distress or working channel as the case may be - and it can be conducted in either voice or telex mode, depending on circumstances.
DSC calls are Selective, because as we have seen above, they can be directed to a selected station or stations. Previously virtually all calls were received by all stations who were in range of the transmission. However, the DSC control unit looks at each call that it receives and determines if the call is addressed to it specifically, to it as part of a group, to all stations, or to vessels in the area where the receiving station is located. When such a call is received then the operator is alerted, usually by a buzzer and an indication on the screen. The information as to where and how the traffic will be sent is displayed on the screen. All other calls are simply ignored.
The last part of the name sums up what DSC is about. It is used for calling another station to advise them that there is traffic for them, and to what channel or frequency they should tune their radio to receive this traffic. When a DSC call is transmitted by VHF, it is sent in F1B modulation, at a speed of 1,200 baud. At this speed, all the data in a DSC Alert can be transmitted in about half a second. On MF/HF things happen just a little slower. The modulation is J2B and the speed of transmission is 100 baud. This results in a DSC Alert on MF or HF taking between 6 and 7 seconds to be transmitted. The DSC control unit transmits the DSC calls through the ship's VHF and/or MF/HF radio. Although installations and equipment obviously vary, the control unit is normally also connected to a dedicated receiver which monitors the DSC frequencies for incoming DSC calls, regardless of to which frequencies the ship's radios are tuned.
Friday, 27 February 2009
How to avoid typhoon during sailing
When the typhoon approach, the barometer reading drops rapidly.
When the typhoon approch, the wind veers to the left. When the typhoon is leaving you, the wind veer to the right irrespective to which hemisphere you are sailing, N or S.
Tuesday, 24 June 2008
Monday, 16 June 2008
Goodbye to sailor who died with valor
Nearly 700 sailors, co-workers and friends crowded into the Clear Lake United Methodist Church on Thursday to say goodbye to veteran seaman Roger Stone, who died saving the lives of two students as their sailboat capsized in stormy seas.
"Roger was my friend and he demonstrated uncommon valor," Mike Janota, Stone's sailing partner for 25 years, told those at the memorial service.
Stone, 53, was the first to recognize that the keel had dropped off the Texas A&M University at Galveston sailboat, the Cynthia Woods, at about 11:45 p.m. Friday during a race from Galveston to Veracruz, Mexico.
Realizing that they had only seconds before the boat capsized, Stone hustled students Steven Guy and Travis Wright into the gangway.
Stone pushed Guy out as water rushed in, enabling Guy to struggle to safety underwater by grabbing the wheel and pulling himself toward the stern.
Known for his coolness in the face of danger, Stone had saved lives before.
"Roger was a hero well before the weekend," said the Rev. Tony Vinson during the service.
Vinson recounted how in a race two years ago Stone was disqualified after he dropped his sail and turned on his motor to help a competitor whose sailboat was dismasted and its crew thrown into the water, in danger of being swept onto the rocks.
"He basically put himself out of the race," to help the stricken crew, Janota said in an interview.
Stone's sailing skills were legendary.
Janota recalled a race in which a boat with a deeper draft was gaining on them and Janota wanted to maneuver the boat to cut off their competitor.
But Stone calmly calculated their relative positions with a cheap, aging GPS device and told Janota to stay on course. Predicting their opponent would strike the shallow bottom, Stone said, "He's going to run aground just about now," Janota recalled.
"He literally called it on the second."
Roger Winslow Stone was born in London, the son of Doris Lacy Stone, now 90, and the late Richard Winslow Stone. He was raised in Hastings-on-Hudson, N.Y., a suburb of New York City.
He got his first taste of sailing after his father purchased a 13-foot, French-made open hulled sailboat, said his sister, Valerie Stone, 54, of Boston.
After graduating from Bellevue Community College in Bellevue, Wash., with a degree in biomedical photography, Stone accepted a photography job in 1980 at the University of Texas Medical Branch at Galveston.
He met his wife, Linda, in 1987 during a racing event and they were married on June 15, 1990, in Veracruz.
In Galveston he immersed himself in his life's passion, sailing, winning many offshore sailing trophies, family and friends said.
But his devotion to his children, Eric, 14, and Elizabeth, 12, was stronger than his love of sailing, family and friends said. Janota recalled him announcing unabashedly to a room of shocked sailors that he would not race in one of the most important races of the year because he had to accompany his daughter on an Indian Princess outing.
His ashes will be scattered at sea Saturday, Janota said.
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