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Old 26-07-2012, 20:10   #16
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Re: Mayday ignored?

As people have already explained, HF/SSB can go long distances. VHF is possible but not normally higher than 70MHz. try looking up Tropospheric/Tropo Ducting/Propagation. From this, I've heard of people communicating on VHF long distances, even accidentally because of this.
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Old 26-07-2012, 20:28   #17
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Re: Mayday ignored?

I was in a control tower one evening, sky was full of ice crystals, their VHF was sporadically picking up calls from several hundred miles away. The controller remarked that it happened occasionally due to atmospheric conditions.
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Old 26-07-2012, 21:10   #18
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Re: Mayday ignored?

I spent a life time in the Coast Guard, and I've heard a lot of stories about VHF, but never Bahamas to Alaska. SSB is a questionable and unreliable way of communicating a distress 24 hours a day. My father was a Ham operator years ago (K6AWL) in San Diego, and he talked on a "skip" when things were just right, using the earth's atmosphere, all over the world. I've watched SSB work and not work during distress cases. We are in a strange situation, as the time of day makes a lot of difference on how far your signal will go depending on the time/frequency. Worst case is when you are 50 miles from the Coast Guard station, and the signal jumps right over their antenna. You can be too far (>20 miles) for VHF and too close for SSB. I was stationed on three different LORAN stations in Europe, and we had to change frequencies throughout the day, every day, to talk to the LORAN stations all day long, in Italy, Spain, Turkey and Lybia to keep the LORAN signal in perfect timing. One of my pet peeves is that we have one main distress frequency (2182), and it isn't always perfectly receivable, all day long. That's why I continue to stress EPIRBs. Sorry, I just know too much about SAR and care about all of you cruisers....
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Old 27-07-2012, 06:14   #19
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Re: Mayday ignored?

Quote:
Originally Posted by Cyrus Safdari View Post
I guess that maybe some of the other boats were not monitoring their radios...
Or just not really listening to what was coming across. Not at all unusual, really. A lot of people have their radios on, but almost nothing that comes across actually registers in their brain. Once in a while they stop and listen for a few moments, but most of it is just background noise to them.

That's one reason that I deliberately turn my radio off most of the time. If it is on I want to pay attention to what is coming across. If I am not paying attention then I will turn it off. I don't want to let it become background noise that I get into the habit of just ignoring.
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Old 27-07-2012, 11:27   #20
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Re: Mayday ignored?

I'm in the Bahamas but if I'm at anchor the VHF is usually off after 2100 hrs or so.
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Old 27-07-2012, 17:17   #21
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Re: Mayday ignored?

The other problem with cruisers is that while in foreign waters we tend to listen to the cruiser channel while at anchor, but use channel 16 when moving... So unless someone is scanning channel 16 they probably won't here an emergency call.

This bring up a point of Digital Selctive Calling (DSC)... Make sure your radios are set up for DSC and the crew knows how to use them...

DSC automatically switches your VHF to channel 16 or a working emergency frequency on SSB and sounds an audible alarm... It is hard to miss an emergency DSC call if you radio is on, no matter what channel or frequency your radio is set on.
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Old 28-07-2012, 18:36   #22
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Re: Mayday ignored?

I saw this thread and thought maybe I could sort out a few issues, and help some here....


This post will be in three brief parts....

Part A = A better description of what happened in the referenced incident...
Part B = What communications gear is best used in situations like this, and how to use it...
Part C = A very brief overview of radiowave propagation...



~~~~~~~~



Part A....
Without going into too much detail of the author's article, here are few points of clarity....

For those that didn't read the article,the author explained why she did not activate their EPIRB..

And for clarity and explanation here, the author's vhf (ch. 16) mayday calls WERE HEARD CLEARLY by many people within 20 miles of their position, some were other cruisers/sailors, some were local Bahamians, and one was a passaenger ship, "Bahamas Celebration"...
This local cruise ship (Bahamas Celebration) was the only one to respond to the aurthor's vhf (ch. 16) mayday calls...
The author found out a couple days later, that many had heard her calls, but none responded (apparently as they could not offer direct assistanace, they assumed they should do nothing, not even respond and attempt to relay the distress!!!), as many other cruising boats, and many Bahamian locals, all asked how they survived / how they were doing / etc....


Due to draft and size, the "Bahamas Celebration" could not provide direct rescue, but offered to relay their distress to the Bahamas Air Sea Rescue..
The author declined this, but did get the captain's cell phone number to call him back, should they find that they did need rescue after all....


The author, with her husband now back on-board (he grounded the dinghy and walked/waded his way back to their sailboat), summoned assistance from another cruising boat anchored 1/2 mile away (using spotlight), and with his and his dinghy's help, (and a rising tide) they were able to kedge-off and float free....


I will leave my astonishment (and disgust) over nobody repsonding to her mayday calls aside here....and let everyone here decide just what good seamanship (and being a decent human being) actaully means....



~~~~~~~~~~~~~



Part B.....

An unfortunate fact is that some cruising sailors ignore the standards of good seamanship (and ignore COLREGS, etc.), and do not maintain a radio watch while at sea....and many (most?) do not maintain a radio watch when at anchor....

But, here is where DSC makes life SO MUCH EASIER!!!


Tom makes a good point here....
Quote:
Originally Posted by jeremiason View Post
This bring up a point of Digital Selctive Calling (DSC)... Make sure your radios are set up for DSC and the crew knows how to use them..
While at sea or in remote anchorages if monitoring ch. 16 (or ch. 13 / 16, in dual watch), your vhf is uaually silent for days at a time, some who sail from crowded/populous areas are acustomed to constant chatter/traffic on ch. 16, etc. and elect to not listen and/or not monitor, and this habit prevades into areas (at sea or remote anchorages) where it would be prudent to maintain a radio watch....and here is where vhf-DSC watch can offer a "win-win" solution...


{Unfortunately, in this specific incident (wrote about in the referenced article), if the author had vhf-DSC equipment this would most likely not made any difference at all....and possibly some who heard her voice mayday call may not even have a vhf-DSC radio....so if time allows, in addition to pushing the DSC DISTRESS button, doing a voice Mayday call on ch. 16 is also advisable....}


To her great credit, the author knew what frequencies to try to attempt to contact the USCG using voice on SSB....kudos!!
http://www.navcen.uscg.gov/?pageName=cgcommsCall
But, what is really needed here in this thread, is an understanding of radio propagation (see below), and an understanding of how DSC works (beyond the scope of this thread), and how MF/HF-DSC could really have helped...


Just a brief overview here....

Doing a "6-frequency" / all-channel MF/HF-DSC-Distress call (which takes all of about 5 seconds to do), from an Icom M-802 transceiver (or other MF/HF-DSC transceiver), would have transmitted the vessel's distress (and GPS position) to all SOLAS-grade vessels within range (25miles to 4000+miles) AND to the USCG stations, on all 6 GMDSS Int'l DSC frequencies (2187.5 4207.5, 6312, 8404.5, 12577, and 16804.5), over and over.....increasing chances of their distress being received many, many times over....

The use of the "six-freqs" reduces/removes most of the guess work from attemping to raise assistance using HF radio, AND the use of high-reliability digital signaling (able to operate effectively with much reduced signal levels and S/N ratios, where voice communications is NOT possible), increases the chances of being heard / getting accurate information (distress and GPS position) passed to those who can provide assistance / rescue....

To be clear, nobody can 100% "gauruntee" that MF/HF-DSC signaling would have worked in this specific incident, but I'm 99% sure...


To be blunt, since Jan 1999 there has been NO MF/HF/VHF voice radio watch keeping required by vessels at sea, nor coast radio stations....(that's 13.5 years ago....how many people use the same computer, or cell phone, that they used 13 years ago....or even the same EPIRB.....but for some reason many sailors seem to think that their radios are "just fine"....and I'm left wondering why???)
The GMDSS provides for DSC radio watch keeping....

And, in my opinion, everyone should understand this and equip their vessels accordingly.....and make sure they know how it all works!!!



~~~~~~~~~~~~~~~



Part C....

A detailed, in depth discussion of radio wave propagation is well beyond the scope of this thread (and on-line disc here, in general)....


But, in brief....

1) HF radio propagation can be frustrating at times...


2) Getting rid of HF RFI (your received radio noise interference) on-board your boat can be very important to HF voice comms, as YOU not hearing well, makes you try another channel/frequency, when you'd be better off using the "right one" and making multiple attempts at raising assistance...
The use of PACTOR modems on-board so many vessels (with their error-correction, etc.), seems to have lulled some cruisers into a false sense of ease / "plug-n-play", in my opinion a least...


3) Wintertime / Nightime lower frequency HF communications, DO take place over very long distances (3000-4000miles is common).....
And, "grayline" propagation (usually not just along the grayline, but when one station is just past sunset or just before sunrise) on low hf frequencies can be outstanding!!! (such as the author realized, raising NOJ, USCG Station, Kodiak, AK on 4125mkz...from the northern/central Bahamas..when Kodiak was just after sunset....)

{I, myself, have regularly communicated from central Florida to the UK, EU and Mid-East (4500 - 6000 miles) for hours and hours at a time on 3795khz, with no special conditions.....and from Florida to Australia (11,000 miles) on 3795knz SSB, "grayline comms" for about an hour or so, when nearing sunrise in FL and just after sunset in Aus....}




4) Although not applicable to the incident in the article, some here have questioned/commented on long distance vhf communications....simple SSB and CW contacts over thousands of miles (depending on "type of propagation") are not uncommon.....


As an example the first ham radio vhf (144mhz) contacts between California and Hawaii (~ 2400 miles) took place in 1957!!!! Using radios with vacuum tubes!!!! (Tropo-Ducting)


Myself, I've made contacts from FL to Wyoming, Colorado, Nebraska, etc. (~ 2000 - 2300 miles) years ago...(Es-skip).....and regularly make contacts past 700 - 800 miles using tropo-scatter (no enhanced propagation modes)....
As well as bouncing my signal off the moon, and communicating with other hams (~495,000 miles...)....


Tropo-scatter is the basic "beyond-line-of-sight" mode of vhf communications, and is NOT a propagation mode that requires ANY enhanced conditions at all....it is "always there".....you just need to have the ERP to overcome the path losses...

Tropo-scatter is a VERY reliable (24/7) communication modes, assuming there is adequate transmit power/ERP/antenna gains, to overcome the path loss, which is easily calcuable....

Normal troposheric enhancement aka "Tropo" (what most laypersons wrongly refer to as ducting) allows vhf comms thru 250 - 400 miles...
This usually occurs with a troposhperic temperature inversion....


Tropo-ducting (over water), can occur for long periods of time (sometimes weeks), depending on weather patterns....and Es-skip (anywhere), which depends on E-layer density of the ionosphere.....
Both allow vhf comms from ~600-700 miles out to 2200-2500 miles.....


There are other long distance vhf comms propagation modes, such as auroral, meteor-scatter, auroral-Es, Field Aligned Irregularites, non-TE F2 (VERY RARE), moonbounce (EME), and Trans-Equatorial Propagation....


The longest terrestrial vhf contacts are to/from the N. hemisphere / S. hemisphere, using Trans-Equatorial (TE) Propagation (F2-skip).....with disatnces of 4000 - 5500 miles....


And, with modern low-speed data comm techniques (using computers) these disatnces have continued to grow....


If you wish to see some documentation...have a look at some records...
http://www.arrl.org/distance-records
http://www.ham.se/vhf/dxrecord/dxrec.htm#C
http://www.vhfdx.info/tep.html



~~~~~~~~~~~~~~~




I hope this helps clarify some things....


Fair winds...


John
s/v Annie Laurie
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Old 06-08-2012, 09:50   #23
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Re: Mayday ignored?

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Originally Posted by ka4wja View Post
The author found out a couple days later, that many had heard her calls, but none responded
This is what amazed me -- I wish the article had discussed this issue more.

The author was quite clear in her Mayday and she repeated it thrice so I just don't buy the idea that no one noticed or wasn't paying attention. They heard it, knew it was a mayday, and ignored it.
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Old 06-08-2012, 14:58   #24
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Re: Mayday ignored?

Quote:
Originally Posted by ka4wja View Post
[B]


The author, with her husband now back on-board (he grounded the dinghy and walked/waded his way back to their sailboat), summoned assistance from another cruising boat anchored 1/2 mile away (using spotlight), and with his and his dinghy's help, (and a rising tide) they were able to kedge-off and float free....


I will leave my astonishment (and disgust) over nobody repsonding to her mayday calls aside here....and let everyone here decide just what good seamanship (and being a decent human being) actaully means....
Sorry if I take this off the discussion of radio wave propagation but I am interested in the actual distress and rescue.

What is the purpose of Mayday, distress calls and calls for assistance. At the basis is saving or protection of life.

It sounds like the boat was wading distance to shore. Where was the life threatening situation here?

Yes someone's boat was on a reef and likely in danger of breaking up but simply dinking to shore would save the human life in this case.

I don't want to be insensitive to the boat owners but this seems like a danger only to the boat.

What would be interesting to know is what were the exact radio calls she made. If it was basically the boat is stuck and going to be in trouble but we are 20 meters from shore I can see why some people did not rush to assist.
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Old 06-08-2012, 15:09   #25
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Re: Mayday ignored?

But Dan that is a different issue (I agree it may not really have been a Mayday situation). But the people who heard the Mayday and didn't respond and then forward it etc didn't really know that did they? If I ever have to do a Mayday I hope people who hear it don't say to themselves "that doesn't sound a life and death issue so I'm going to ignoe it".
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Old 06-08-2012, 15:36   #26
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Quote:
Originally Posted by ka4wja
I saw this thread and thought maybe I could sort out a few issues, and help some here....

This post will be in three brief parts....
Brilliant post. Thanks for taking the time...
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Old 06-08-2012, 15:38   #27
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Re: Mayday ignored?

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But Dan that is a different issue (I agree it may not really have been a Mayday situation). But the people who heard the Mayday and didn't respond and then forward it etc didn't really know that did they? If I ever have to do a Mayday I hope people who hear it don't say to themselves "that doesn't sound a life and death issue so I'm going to ignoe it".
"Due to draft and size, the "Bahamas Celebration" could not provide direct rescue, but offered to relay their distress to the Bahamas Air Sea Rescue..
The author declined this, but did get the captain's cell phone number to call him back, should they find that they did need rescue after all.... "

I did not see a link to the whole article but there seems to be more going on with the situation.

They did not activate the EPIRB, someone was responding and offering to relay their distress but was refused.

If I were listening to the radio calls I would be hard pressed to "butt in."

I am baffled why one would call "mayday" and then refuse to accept an offer to get the official rescue folks involved.

It is still not clear what sort of assistance the couple wanted.
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Old 07-08-2012, 12:35   #28
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Re: Mayday ignored?

Quote:
Originally Posted by Ex-Calif View Post
"Due to draft and size, the "Bahamas Celebration" could not provide direct rescue, but offered to relay their distress to the Bahamas Air Sea Rescue..
The author declined this, but did get the captain's cell phone number to call him back, should they find that they did need rescue after all.... "

----

They did not activate the EPIRB, someone was responding and offering to relay their distress but was refused.

If I were listening to the radio calls I would be hard pressed to "butt in."

I am baffled why one would call "mayday" and then refuse to accept an offer to get the official rescue folks involved.
I agree with Dan - if I heard somebody refusing a comm attempt with BASRA I would write it off as a non-mayday situation.
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Old 07-08-2012, 12:57   #29
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Re: Mayday ignored?

I think the proper procedure is creating some of the problem. When you receive a DSC distress call you are not supposed to respond for 5 minutes. The CG shore station is supposed to respond. I think this makes people sit there and wonder when or if they are supposed to respond.


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Old 07-08-2012, 13:25   #30
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Re: Mayday ignored?

Would be also interested what content the Mayday call was. Reason : Normally you would provide your position in the Mayday message. Wonder how many thought it was a joke, because obviously her position was basically ashore.

@ka4wja : totally agree ... ppl spend very large amount for their boat and are not willing to spend a few (hundred) bucks for a proper DSC radio station. Also I would really recommend to do at least a VHF radio course (such as RYA SRC). Cost you nothing but you learn the basics.

PS : in the course she would heave learned not to send a "mayday" in her case
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