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Old 01 September 2012, 18:26   #41
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Besides, if it was on fire then I wouldn't be using the handheld DSC, I would still be on the boat
Oh dear more torkin bollox
Hmmm - say 90 litres of petrol onboard
you have obviously not seen as I have the damage that a half litre of petrol in a 3,000 gallon tank can do when the fitter tried to loosen an access bolt with a blowlamp. Dual compartment 6,000 gallon brand new steel underground storage tank in the hole but not yet backfilled with the concrete . The petrol had been put into the suction pipe to hold the non return valve shut during a pressure test, then released into the tank afterwards. Fortunately for the fitter he had fitted the vent to the other compartment first. Blew out the centre steel division and seared the wall for 20ft up around the vent pipe for the other compartment.
If a petrol powered small boat is on fire I'm going for the early bath option thank you
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Old 02 September 2012, 05:15   #42
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Originally Posted by gotchiguy View Post
No it won't send an old position.
Icom M91 Manual - page 25 ( http://www.icom.co.jp/world/support/.../IC-M91D_0.pdf )

"NOTE: The distress call is paused for up to 15 seconds
when no valid position data is received. The distress call
is made when a valid position data is received within 15
seconds.
If valid position data cannot be received within 15 seconds, the
distress call is made with a stored position data."

Err.. so it WILL send an old position. I dont see any menu to switch off GPS on the Icom although I may be missing it. But if not then there should only be no possition if the radio is just switched on or the signal is obscured for some reason.

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As Gotchi says, the Standard Horizon 851 does not suffer with any of those problems...
Unless I am mis-understanding the HX851 Manual if you've switched off GPS it doesnt try and reenable it to send the alert. So you are sinking, its cold and wet and you now have to remember to re-enable the GPS wait for a fix (38 seconds if you haven't disabled it too long ago) then hit the magic red button... ...not sure why thats "not a problem"

Copinsay reports a 38 second fix. The longer power saving modes on the HX581 switch on the GPS for 50seconds every X minutes, which makes sense. From past experience with GPSs they take longer to fix the further you've moved from the last fix, and longer if moving. Wiki backs that up (Time to first fix - Wikipedia, the free encyclopedia) - the difference between cold and warm fixes not being the length of time since the GPS was last used but the change in location/speed... So if you switch on your GPS every hour while underway at 30kts it may slow down the fix when stopped and sinking and have lost electrics on your fixed set. Although the manual does seem to think that should still be 1 minute. But I want to hit the big red button and wait for an aknowledgement not have to go through a series of menus wasting time.

I'd far rather have my GPS updating every 5 minutes than when I remember to switch it on and off. At 30kts 5 minutes is still 2.5nm or a search area of nearly 20 nm.sq A judgement of how long help will take, how easy you'll be to find (other boats make locating you difficult), what form help is likely to be*, and a potential search area (based on speed) may well mean you'd be better using a lower update time.

*a rural location with helicopter - you may be easy to spot. rural location from the water may take far longer. crowded sailing waters from helicopter you are one of several hundered boats from the water there are several hundered other boats who can help you.

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Originally Posted by Channel Ribs View Post
Even if a DSC radio were to send an old location, it would mark it as such and the speed and direction info would still be valuable to the rescuers.
I can't see any sign that the M91 transmits direction or speed information in its DSC message? Does the HX851? Does any DSC Cat D Radio? Unlike big ships RIBs tend to manouvre a lot more and change speed a lot more. Someone circumnavigating the IOW leaving the solent in a roughly Easterly direction at 30kts and hour ago could well be somewhere South of Ventnor not Poole as it might appear... OK so Solent CG have a brain and can work out that they might have a very large search area but would it not be better to have a more realistic possition in the first place.
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Old 02 September 2012, 05:32   #43
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You seem to be saying that even if I am right then there is still a reason not to like handheld DSC?

But FWIW and AFAIK... The data sent in a DSC message is:-

Latitude, Longitude, Date and time of fix, Course over ground and Speed over ground.
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Old 02 September 2012, 05:50   #44
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No it won't send an old position. Besides, if it was on fire then I wouldn't be using the handheld DSC, I would still be on the boat and therefore able to use flares/fixed DSC/AIS not to mention PLB permanently on my lifejacket
Notwithstanding wavelength's very good point about why an early departure from a boat on fire might be wise, even a small fire has the potential to wipe out all your on board electrics. Might I ask why you have have a DSC handheld if you always plan to be on board the boat with a working radio and a PLB on your person as a backup if you go for a swim?

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Originally Posted by Channel Ribs View Post
You seem to be saying that even if I am right then there is still a reason not to like handheld DSC?

But FWIW and AFAIK... The data sent in a DSC message is:-

Latitude, Longitude, Date and time of fix, Course over ground and Speed over ground.
Course and speed are not part of a normal DSC distress message. The time of fix IS part of the message.
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Old 02 September 2012, 05:58   #45
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Hi all

Out of interest - can someone tell me please what DSC data is sent when making a routine traffic call to the coastguard?

I ask because as there is no signal at one of the slipways I use, I have to call in when 500m out at sea, or at the top of the hill in the car, and wondered if that would be apparent / confusing to the CG?

Steve
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Old 02 September 2012, 06:04   #46
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Course and speed are not part of a normal DSC distress message. The time of fix IS part of the message.
Thank Pol, do you have a reference for that? I have had this discussion a few times.
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Old 02 September 2012, 06:29   #47
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Thank Pol, do you have a reference for that? I have had this discussion a few times.
The definitive source is here: http://hflink.com/selcall/ITU-R%20M-493-11.pdf

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Originally Posted by Copinsay View Post
Hi all

Out of interest - can someone tell me please what DSC data is sent when making a routine traffic call to the coastguard?

I ask because as there is no signal at one of the slipways I use, I have to call in when 500m out at sea, or at the top of the hill in the car, and wondered if that would be apparent / confusing to the CG?

Steve
No position information is sent to with a standard call (to the CG or another station). Positions are only sent with either a distress call or responding to a specific "position request" (position poling).
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Old 02 September 2012, 07:06   #48
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The definitive source is here: http://hflink.com/selcall/ITU-R%20M-493-11.pdf
Cracking stuff, thank you.

So the data that is sent is position and time of position, if neither are available then they are marked as such.
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Old 02 September 2012, 07:47   #49
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Many thanks from me too.

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Old 02 September 2012, 09:19   #50
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You seem to be saying that even if I am right then there is still a reason not to like handheld DSC?
Not at all - nothing to do with being handheld or not. I was questioning the practice of switching off the GPS to conserve battery power, when in my opinion it compromises the functionality at the time it might be most needed, i.e. in a hurry to send a possition as part of a distress message.

Handheld DSC is inherintly sensible as a tool, free from other dependancies like 12V batteries, external antena, external GPS, NMEA cables that are usually just twisted bits of wire, being screwed to the boat and not being able to come with you.
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