Why the reluctance to call for help?

[CatB]

Originally Posted by Mark Chase

True but look in the BSAC reports. Plenty of divers got bent in 25m of water.

ATB

Mark

I didn't mean to suggest that they wouldn't get bent. Only that in these cases people would be less likely to have multiple possible deco plans (where they may or may not have missed stops that were buit in for conservatism and so on) and to be carrying out self checks so it might be less controversial to contact the coastguard for advice.

Chrisch asked about single tanks and deco so I pointed out that although I'd be on a single tank, others wouldn't necessarily and so may be doing a relatively small amount of deco (compared to what has been discussed). They could still miss these stops and get bent (or not and still get bent!). However if they had 20 mins of stops and missed the lot - in my eyes (and I'm willing to be corrected on this) that would be a clearer reason to contact the CG than someone who had 3 hours of stops and built in a safety margin on top of a conservative model and so on then decided to shorten it by 20 minutes. I am highly unlikely to be on a boat with people doing 3 hour deco and thus I am not going to worry about arguing with them about calling the coastguard!

On the kind of trips I do, personally I think 20 mins of missed stops would be a good reason to call and get advice from the dive Dr.

I think that was my point originally (although I'm starting to loose track of everything now!).

Maybe we should just look at the way people voted on Janos's scenarios poll and choose our boat companions accordingly!

[Mark Chase]

Originally Posted by CatB

I didn't mean to suggest that they wouldn't get bent. Only that in these cases people would be less likely to have multiple possible deco plans (where they may or may not have missed stops that were buit in for conservatism and so on) and to be carrying out self checks so it might be less controversial to contact the coastguard for advice.

Chrisch asked about single tanks and deco so I pointed out that although I'd be on a single tank, others wouldn't necessarily and so may be doing a relatively small amount of deco (compared to what has been discussed). They could still miss these stops and get bent (or not and still get bent!). However if they had 20 mins of stops and missed the lot - in my eyes (and I'm willing to be corrected on this) that would be a clearer reason to contact the CG than someone who had 3 hours of stops and built in a safety margin on top of a conservative model and so on then decided to shorten it by 20 minutes. I am highly unlikely to be on a boat with people doing 3 hour deco and thus I am not going to worry about arguing with them about calling the coastguard!

On the kind of trips I do, personally I think 20 mins of missed stops would be a good reason to call and get advice from the dive Dr.

I think that was my point originally (although I'm starting to loose track of everything now!).

Maybe we should just look at the way people voted on Janos's scenarios poll and choose our boat companions accordingly!

Oh I absolutly agree


However one must understand the anomalies of diving computers.

As I posted previously I have suposedly missed 30mins of stops on a Sunnto on a red sea reef dive.


They refuse to credit deco at 8m


So imagine the scinario if you will.

Your diving the Roseleemulla in a bit of tide (35m). As per usual the dive guides push the gas or the NDLs but your all good sac and on 15's

Big dive for you so you set your Suunto to +3 safety.

You do the same 30min bottom time as the others but you rack up 15mins of stops.

You ascend the shot with the others, but tides running and you have to hang on.

Your stuck at 8m because all the others are above you on the shot.

Your suunto isnt counting down. If anything its counting up.

Your low on gas and yet your deco has still not cleared

You end up surfacing and bending the Suunto

You have missed 10mins of stops.

Do you call the rescue boat and get off the liveaboard mid holiday and get to the deco chamber or do you asses the situation logicly and just get a compitent diver to keep and eye on you / check you out?

ATB

Mark

[TerryH]

Originally Posted by Mark Chase

Do you call the rescue boat and get off the liveaboard mid holiday and get to the deco chamber or do you asses the situation logicly and just get a compitent diver to keep and eye on you / check you out?

If you buy a bit of kit with a known set protocol, then you shoudnt be
surprised if it freaks out when you create a scenario that breaks that
protocol.

I suppose I would (like you have) purchased the right make of computer
that doesnt penalise me for doing stops at 8m.

Then you'd be back on the boat with your mates, wouldnt you?

[Woz]

Originally Posted by Mark Chase

Oh I absolutly agree


However one must understand the anomalies of diving computers.

As I posted previously I have suposedly missed 30mins of stops on a Sunnto on a red sea reef dive.


They refuse to credit deco at 8m


So imagine the scinario if you will.

Your diving the Roseleemulla in a bit of tide (35m). As per usual the dive guides push the gas or the NDLs but your all good sac and on 15's

Big dive for you so you set your Suunto to +3 safety.

You do the same 30min bottom time as the others but you rack up 15mins of stops.

You ascend the shot with the others, but tides running and you have to hang on.

Your stuck at 8m because all the others are above you on the shot.

Your suunto isnt counting down. If anything its counting up.

Your low on gas and yet your deco has still not cleared

You end up surfacing and bending the Suunto

You have missed 10mins of stops.

Do you call the rescue boat and get off the liveaboard mid holiday and get to the deco chamber or do you asses the situation logicly and just get a compitent diver to keep and eye on you / check you out?

ATB

Mark

5m is where the Suunto wants you to be. I did a bit of testing and if you sit at 6, you'll be there forever. 5 (which conincides with the PADI RDP wheel) the Suunto loves it and the minutes fly by.

[CatB]

Originally Posted by Woz

5m is where the Suunto wants you to be. I did a bit of testing and if you sit at 6, you'll be there forever. 5 (which conincides with the PADI RDP wheel) the Suunto loves it and the minutes fly by.

Indeed. In fact I did do something similar to Mark's scenario on exactly that wreck except that my buddy and I watched our computers and had agreed that we'd go up with no more than 3 mins of stops at the bottom (with or without the dive guide) 'cos I was on a single with no redundancy - which we did and they'd cleared by 8m. We still had a safety stop to do according to the computers and the Suunto insists you are above 6m for this. A bit of shuffling on the shot and some apologetic hand signals and the whole group had got themselves into positions where their respective computers were counting down nicely.

I'm still a relative newbie and although I know some of the limitations of a computer I would do my utmost not to get into a situation where I had to bend my computer or run out of air. Especially on a liveaboard where it would mean that the rest of my diving would have to be done on tables while my computer sulked in my cabin.

If someone else on the boat had proceeded according to the scenario Mark gave and ended up bending their computer I would probably make sure the guides knew and I would keep an eye on them myself - but I think it would be up to them and the guides how they proceeded. In that situation there is someone on the boat responsible for the diving going on and that is the guide.

I think we all need to apply common sense on the day - it's useful to have these kinds of issues raised but you can't plan for every scenario, just generate some broad criteria in your mind as to what you would do in different circumstances.

[MattS]

Originally Posted by Woz

5m is where the Suunto wants you to be. I did a bit of testing and if you sit at 6, you'll be there forever. 5 (which conincides with the PADI RDP wheel) the Suunto loves it and the minutes fly by.

When the 88s came out 6m was regarded as the theoretical maximum depth you could dive to for an infinite length of time without getting bent. British divers have clung to 6m as the last decompression stop depth ever since.

Shortly after the 88s were published the theoretical maximum never stop depth was reviewed and made a little shallower. So the RDP (modified USN/Haldanian) used 5m for the safety stop depth. Buhlmann used 3m for the last stop depth, which was copied by Suunto and most of the other computer manufacturers. IANTD used 4.5m to compromise for real sea conditions. IIRC there are references in DID and on the VPlanner site.

The Suunto's slowness to clear decompression at 6m (is most likely) due to implementing less compartments than Buhlmann's original 16. It introduces some lumpy-ness to the profile prediction. Uwatec's used to do a similar thing. Nick Bushell (Pro Planner) kindly explained to me what was going on.

I first came across this feature of decompression models after a dive on the M2 using an Aladdin. I completed my last stop at 6m but padded it by a couple minutes. Between leaving 6m and arriving at the surface the computer added a further 3 minute at 3m stop. I didn't know about the additional stop until I was on the surface when the computer started to bleep and flash SOS. I had more experience deco diving on 88s than on computers in those days, so decided not to call CG as the profile was no where near the 88s no-stop limit.

Anyhow it demonstrates a limitation of deco-models pretty well. Your body isn't a neat arrangement of hypothetical compartments and half-times and it doesn't behave quite so predictably.

[Mark Chase]

Originally Posted by TerryH

If you buy a bit of kit with a known set protocol, then you shoudnt be
surprised if it freaks out when you create a scenario that breaks that
protocol.

I suppose I would (like you have) purchased the right make of computer
that doesnt penalise me for doing stops at 8m.

Then you'd be back on the boat with your mates, wouldnt you?

Yeah but not many single tank dudes with VR3's

You shouldn't be surprised that some STDivers new to the game would have no understanding of this set protocol.

My wife couldn't figure out why I was insisting she went up when her Marres Surveyor was still showing 3mins of stops.

This was because every time she accidentaly dropped below 5m it re-set and asked for ANOTHER 3min safety stop. After the third i got fed up. However she had a right go at me for making her miss her stops

ATB

Mark

[JasonP]

Originally Posted by MattS

The Suunto's slowness to clear decompression at 6m (is most likely) due to implementing less compartments than Buhlmann's original 16. It introduces some lumpy-ness to the profile prediction. Uwatec's used to do a similar thing. Nick Bushell (Pro Planner) kindly explained to me what was going on.

The 2nd generation Uwatec Aladin Pros take twice as long to clear a 3m stop at 6m. We timed it once.

Jason

[TerryH]

Originally Posted by Mark Chase

You shouldn't be surprised that some STDivers new to the game would have no understanding of this set protocol.

I'm not, but then I wouldnt expect anybody "new to the game" to be at
35m on the Rosalie Moller.

[MattS]

Originally Posted by JasonP

The 2nd generation Uwatec Aladin Pros take twice as long to clear a 3m stop at 6m. We timed it once.

From what I remember of the maths that makes sense.

Where the depth/time relationship is obviously non-linear it indicates a change in the controlling compartment or the influence of some arbitrary conservatism fudge.