Why do people add a few minutes to their last deco stop?

[Tassi Devil Diver]

Can you explain what you mean?

This sentence could be used to describe the old deep stop theory held by some, who said that doing deep stops ("adding minutes to the final ascent") allowed you to cut short the last deco stops.

No nothing about cutting short the last stop.

I find I get certain niggles if I ascend from the last stop at 6m to the surface at the "normal" rate on deep dives (70-100m) that require long deco (90 plus minutes).

I now set my shallowest stop at 3m, when 6m stop clears I continue to hang out 6m (usually because it is more comfortable), however with 10 min remaining on the 3m stop I very slowly ascend to 3m (<1m/min can take 5min), clear the 3m stop then very slowly ascend to the surface.

This is regardless of my GF high stetting which has ranged from 65-85.

I find since following this ascent approach, I feel much better rather than just adding time on to the last deco stop or dropping the GF high and ascending as "normal".

 

[crofrog]

I know GUE advocates this to a degree, but I wonder if any other agencies do? I believe GUE is 9 m/min to 50% depth and then 3 m/min from there. I know some divers will do 1 m/min from the last stop, but I'm not sure if that's "official" or not. Regardless, I feel that the final ascent (even from the safety stop for rec divers) should be quite slow.

The literature has 1m/min in it for t2 and it is taught in t1 by at least some instructors.

 

[Germie]

The literature has 1m/min in it for t2 and it is taught in t1 by at least some instructors.

I also teach this. It is not required, but it does not hurt for sure. I also use the 9 and 3m-minute during deco. Where the time from 1 depth to a shallower depth is calculated as decompressiontime.
I also still teach runtime tables which more and more technical divers have no knowledge of. They look at it in Multideco or another program and then take 2 Shearwaters and jump in the water.
I practise in a course at least 1 time with a runtime table. Computers can be used, but the runtime table is followed.

 

[Scared Silly]

I have not read the whole 10+ pages and perhaps someone has already said this but one needs to keep in mind that regardless of the algorithm being run, it is a non-ideal model of the average human body. Adding a bit to the last stop helps with the non-ideal bit of the model because none of us are average.

 

[Alex Ouroboros]

ok let’s take things one step at a time, you specifically mention this with regard a safety stop which is not the same as deco stop, (much difference)
IMO this practise is not a bad one for a few reasons, of course these reasons only qualify if the pro,s in a given situation outweigh the cons, ie needing to reboard a boat as it’s near rocks, gas running low etc. firstly any type of diving using compressed gas (oxygen would be the only exception) is forcing nitrogen bubbles in to the blood stream so when ascending from a dive like it or not the body is decompressing albeit in the case not requiring an actual decompression stop, the 3minute safety stop is to allow the blood to expel most of this nitrogen back out as I’m sure you are aware and to further minimise the chance of bubble formation (bad) in each minute the blood in your body does a full circuit between 1-3 times so as the tiny bubbles do yet another lap your body has more chance of getting them out through the lungs, as a result each additional minute adds to the amount of tiny bubbles being expelled, so less residual nitrogen the better,,,plus the diver practises more hover skills (usually) as a bonus, sorry I had to drone on but an explaination is better than a yes or no in this case (this is a very simplified explaination if you want it even more boring I can provide )

 

[Nemrod]

My instructor says he'll often add a few minutes to his last deco stop, and I've seen a few people on these forums mention that they do a similar thing.

It doesn't make a lot of sense to me, when I hear that in my brain I hear "I don't think my deco plan / GFHi is conservative enough so I'm going to add extra deco on top of it". Why not just decrease the GFHi instead of arbitrarily adding a few minutes on the end (Note: I'm not talking about doing the slow ascent from last stop to surface, I'm talking specifically about adding extra time to the last stop before starting the ascent to surface).

My Peregrine does that.* I asked it why but it just stared blankly back at me.

*(Yes, I know, it is in Adaptive Mode)

 

[PfcAJ]

You guys wait for your computer to clear before you surface?

Nerds.

 

[scubadada]

My Peregrine does that.* I asked it why but it just stared blankly back at me.

*(Yes, I know, it is in Adaptive Mode)

Many of us used an adaptive like scheme when close to NDLs, now we have SurfGF and don't have to guess at our surfacing. I have become more conservative as I have gotten older.

 

[Nemrod]

Many of us used an adaptive like scheme when close to NDLs, now we have SurfGF and don't have to guess at our surfacing. I have become more conservative as I have gotten older.

Is the Peregrine guessing ?

 

[dylanfromwinnipeg]

All this discussion has been helpful. Where I think I've ended up is that I don't want to PLAN to spend extra time over and above my computers dive profile. I want to set my GF's so that if everything is going nominally I leave my last stop when my computer says to.

But I can always monitor SurfGF and spend more (or less) time at 6m if the conditions on the dive warrant it.

Something else my instructor taught me is to set my backup computer to have a more aggressive GF, and I can use that one if I'm in an "oh **** I want to surface ASAP" type situation, but still maintain a relatively safe deco profile.