Originally Posted by gotchiguy
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
• 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.
Originally Posted by Channel Ribs
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.
Originally Posted by Channel Ribs
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.