Hammerhead 10 Foot Stop Elimination?

Genesis · 1st March 2006, 21:05

Yes; I am assuming you are flushing with 100% O2 at your 20' stop and carrying on with what is effectively an oxygen rebreather from that point up, yes?

***jradomski*** · 1st March 2006, 21:13

Quote: (Originally Posted by UWSojourner)

Actually, it is controlled by both. Inspired inert gas pressure is a function of BOTH ambient pressure and fraction of inspired inert gas. As you note, at 100%O2, the inspired inert gas pressure is zero ... but when using less than 100% O2, ambient pressure definitely impacts the offgassing rate.

but even if you flush with oxygen it doesn't stay that way for long...

the tissues will offload correctly, but the gf limits are based on current depth, so even if you have say a gf high set to 90, and you are sitting 20 fsw instead of 10, the projected ascent will use the limit for 20fsw (which is a lower GF (or loading limit that must be met), thats why when you ascend past or to the next stop depth it sometimes instantly clears because you now have a higher GF allowed..

the more stops necessary the less you actually notice this behavior, lets make an overly simplistic example, say you have now incurred 2 stops (10, and 20), so in the gf calculations it basically will increase the gf in 3 steps..
so lets use a hypotherical 30/90, once you start an ascent it will be allowed until you reach a 30% load and in this case we will call it, the 20 fsw stop, after this is cleared the gf would be raised to 60, at 10 the eventually the 90 for the surface.. (this means you nead to clear up to 90% so thats the max when you reach it)
now lets say you decided to stay at 20fsw instead of ascending to 10fsw, (20 would have cleared you to proceed to the 10fsw stop with 60%, but if you stayed at 20, it knows what the gradient will be but the limit is still at 60 not the projected 90 because you havent gone there yet)

I hope that clears it up a bit.. This doesnt happen with table because you never "overstay" the stop, as the number of stops increase the steps become much smaller.. On dives with relatively short deco, you are much better off putting the gf low and gf high limits fairly close together and manually doing deeper stops..

**UWSojourner** · 1st March 2006, 21:24

Quote: (Originally Posted by jradomski)

the tissues will offload correctly, but the gf limits are based on current depth, so even if you have say a gf high set to 90, and you are sitting 20 fsw instead of 10, the projected ascent will use the limit for 20fsw (which is a lower GF (or loading limit that must be met), thats why when you ascend past or to the next stop depth it sometimes instantly clears because you now have a higher GF allowed..

I don't think so. At least it shouldn't be done that way.

Let's say you are at 20ft and your watch indicates you should stay at 20ft. Why does it keep you at 20ft? NOT because you haven't fallen below the 20ft GF, but because if you ascended to 10ft you would violate the 10ft GF.

So, if you tell your watch that the last stop is 20ft, it should only clear if a direct ascent to the surface would not violate your HI GF.

**UWSojourner** · 1st March 2006, 22:18

Quote: (Originally Posted by jradomski)

but if you stayed at 20, it knows what the gradient will be but the limit is still at 60 not the projected 90 because you havent gone there yet)

This may be an indirect result of that "minimim 1 minute stop" requirement imposed by legacy code (that we beat to death), but not a direct requirement of the GF method.

The software, when it notices that it can ascend to 10ft, should simply continue to check to see if the diver can go further, shouldn't it? Why is it stuck checking the 10ft GF for an ascent to the surface?

***ScubaDadMiami*** · 1st March 2006, 23:13

Quote: (Originally Posted by jradomski)

12fsw should have been fine.. I never really saw it delay that much close to the stop (I have seen it being close to the 20fsw stop) .. what was your SP at and what were you really maintaining??

if you have a sp chosen thats really hard to maintain say 1.3 at 10fsw (even 1.2 is quite hard), the deco projection is based on the chosen sp and with rounding and not being able to really get to the sp you tell it the deco will drag on..

I find its better to set the sp to .7 to 1.0 and manually maintain it above this level, the prediction time is much closer..

I had it on 1.0, and I was maintaining 1.2 to 1.3. Flying manually.

***ScubaDadMiami*** · 1st March 2006, 23:17

Quote: (Originally Posted by sensor330)

What is your ascent rate? I called Kevin as I was having the same issue and he said that my ascent rate is to quick. Since than I've watched my ascent rate and haven't had any more long 10' stops. When I dive I usually dive with 2 computers a HH, and HS Explorer. I've found that the HSE and HH agree to with in 2 mins but I've also noticed that the time to surface does not match.

Scott

The first stop called for was at 30 feet. However, we were spending most of the time on the deck, averaging just over 100. So, I did a short stop at 60, 1 minute at 50, 1 minute at 40. I think that when I got to 30, instead of 3 @ 30 that was flashing originally, this went down to 2 @ 30. I can't remember now what it said for 20. I stayed at least what the hand set said and then probably some more.

By this time, it was calling for either 1 or 2 minutes at 10. Remembering that it would take a while for it to clear the 10 foot stop if I go deeper, I moved up until there were divers above me on the anchor line. So, I could only get to about 12 or 13 feet. That's when it stayed on 1 @ 10 for the longest time.

***ScubaDadMiami*** · 1st March 2006, 23:20

Quote: (Originally Posted by n2diving)

One behavior some HH divers on the O2ptima have noticed is a final 1 min @ 10 fsw stop that does not clear for several minutes.... what we have found is wait the one minute by the clock, and then ease up to 9 or 8 feet and it will instantly clear.

Ahaaa! In a way, I think that this is what happened. Finally, the divers above me on the anchor line surfaced. So, I moved up to 10. Waves passed overhead, and I bobbed up to 9 here and there. Poof! It cleared.

I didn't associate clearing with that. I just thought I finally put in the time to clear it.

So, does it only do this at the 10 foot stop?

***ScubaDadMiami*** · 1st March 2006, 23:28

Gee, and I thought I was starting to remember the GF stuff. Because I went from U.S. Navy Tables straight to VPM, I never had more than an intellectual understanding of Buhlman related stuff over the years. Now, I have to start remembering how to apply it.

How about this: Request for ability to set last stop depth made hereby. When can I send in my handset for the upgrade?

***jradomski*** · 2nd March 2006, 09:00

Quote: (Originally Posted by UWSojourner)

I don't think so. At least it shouldn't be done that way.

Let's say you are at 20ft and your watch indicates you should stay at 20ft. Why does it keep you at 20ft? NOT because you haven't fallen below the 20ft GF, but because if you ascended to 10ft you would violate the 10ft GF.

So, if you tell your watch that the last stop is 20ft, it should only clear if a direct ascent to the surface would not violate your HI GF.

Remember we are talking about real time.. when you build tables, when a stop is clear (or your limits for that depth have been reached) it jumps to the next stop and the current gf is recalculated.. The current GF limit is based on the current depth..

The ascent is "clear" to the next stop based on the current GF limit..

when you clear a "stop" all it means is that upon reaching the next level you wount violate that limit..

***jradomski*** · 2nd March 2006, 09:33

Quote: (Originally Posted by ScubaDadMiami)

Gee, and I thought I was starting to remember the GF stuff. Because I went from U.S. Navy Tables straight to VPM, I never had more than an intellectual understanding of Buhlman related stuff over the years. Now, I have to start remembering how to apply it.

How about this: Request for ability to set last stop depth made hereby. When can I send in my handset for the upgrade?

Here is the way I suggest you handle it.., after clearing the 20fsw stop, note the time it says you need to stop at 10fsw, once this period has cleared proceed to 10fsw, and it should be clear or at least damn close.. I know in metric mode it clears correctly when the depth displays 3msw, but there is a delay clearing when in imperial mode and you are at 10fsw or deeper.. I know all the calcs are done in MSW then displayed in fsw, following this logic 10fsw is actuactly the next stop depth (for a truncated integer),

On an older revision (I havent tried it on the current sets) but I remember being at a "10 fsw" stop and just by moving my arm up and down to switch the display between 9 and 10 fsw I could get the 1 @10 to pop in and out..

1st March 2006, 21:05	#11 (permalink)
Genesis Bubbless Box of Death Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Oct 2005 Location: Sunny Florida Posts: 1,394	Re: Hammerhead 10 Foot Stop Elimination? Yes; I am assuming you are flushing with 100% O2 at your 20' stop and carrying on with what is effectively an oxygen rebreather from that point up, yes? __________________ "A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American." http://www.denninger.net http://www.diversunion.org/liability.htm - Fix the Diving Cert racket
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1st March 2006, 21:13	#12 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Home Build Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Home Build Join Date: Mar 2005 Location: "Da" Bronx Posts: 2,899	Re: Hammerhead 10 Foot Stop Elimination? Quote: (Originally Posted by UWSojourner) Actually, it is controlled by both. Inspired inert gas pressure is a function of BOTH ambient pressure and fraction of inspired inert gas. As you note, at 100%O2, the inspired inert gas pressure is zero ... but when using less than 100% O2, ambient pressure definitely impacts the offgassing rate. but even if you flush with oxygen it doesn't stay that way for long... the tissues will offload correctly, but the gf limits are based on current depth, so even if you have say a gf high set to 90, and you are sitting 20 fsw instead of 10, the projected ascent will use the limit for 20fsw (which is a lower GF (or loading limit that must be met), thats why when you ascend past or to the next stop depth it sometimes instantly clears because you now have a higher GF allowed.. the more stops necessary the less you actually notice this behavior, lets make an overly simplistic example, say you have now incurred 2 stops (10, and 20), so in the gf calculations it basically will increase the gf in 3 steps.. so lets use a hypotherical 30/90, once you start an ascent it will be allowed until you reach a 30% load and in this case we will call it, the 20 fsw stop, after this is cleared the gf would be raised to 60, at 10 the eventually the 90 for the surface.. (this means you nead to clear up to 90% so thats the max when you reach it) now lets say you decided to stay at 20fsw instead of ascending to 10fsw, (20 would have cleared you to proceed to the 10fsw stop with 60%, but if you stayed at 20, it knows what the gradient will be but the limit is still at 60 not the projected 90 because you havent gone there yet) I hope that clears it up a bit.. This doesnt happen with table because you never "overstay" the stop, as the number of stops increase the steps become much smaller.. On dives with relatively short deco, you are much better off putting the gf low and gf high limits fairly close together and manually doing deeper stops.. __________________ Joe Radomski CCR Trimix Instructor Trainer ANDI Instructor Trainer Director #10 All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated. Last edited by jradomski : 1st March 2006 at 21:21.
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1st March 2006, 21:24	#13 (permalink)
UWSojourner Pacific Northwest Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Portland Oregon Posts: 556	Re: Hammerhead 10 Foot Stop Elimination? Quote: (Originally Posted by jradomski) the tissues will offload correctly, but the gf limits are based on current depth, so even if you have say a gf high set to 90, and you are sitting 20 fsw instead of 10, the projected ascent will use the limit for 20fsw (which is a lower GF (or loading limit that must be met), thats why when you ascend past or to the next stop depth it sometimes instantly clears because you now have a higher GF allowed.. I don't think so. At least it shouldn't be done that way. Let's say you are at 20ft and your watch indicates you should stay at 20ft. Why does it keep you at 20ft? NOT because you haven't fallen below the 20ft GF, but because if you ascended to 10ft you would violate the 10ft GF. So, if you tell your watch that the last stop is 20ft, it should only clear if a direct ascent to the surface would not violate your HI GF.
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1st March 2006, 22:18	#14 (permalink)
UWSojourner Pacific Northwest Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Portland Oregon Posts: 556	Re: Hammerhead 10 Foot Stop Elimination? Quote: (Originally Posted by jradomski) but if you stayed at 20, it knows what the gradient will be but the limit is still at 60 not the projected 90 because you havent gone there yet) This may be an indirect result of that "minimim 1 minute stop" requirement imposed by legacy code (that we beat to death), but not a direct requirement of the GF method. The software, when it notices that it can ascend to 10ft, should simply continue to check to see if the diver can go further, shouldn't it? Why is it stuck checking the 10ft GF for an ascent to the surface?
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1st March 2006, 23:13	#15 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 2,075	Re: Hammerhead 10 Foot Stop Elimination? Quote: (Originally Posted by jradomski) 12fsw should have been fine.. I never really saw it delay that much close to the stop (I have seen it being close to the 20fsw stop) .. what was your SP at and what were you really maintaining?? if you have a sp chosen thats really hard to maintain say 1.3 at 10fsw (even 1.2 is quite hard), the deco projection is based on the chosen sp and with rounding and not being able to really get to the sp you tell it the deco will drag on.. I find its better to set the sp to .7 to 1.0 and manually maintain it above this level, the prediction time is much closer.. I had it on 1.0, and I was maintaining 1.2 to 1.3. Flying manually. __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
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1st March 2006, 23:17	#16 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 2,075	Re: Hammerhead 10 Foot Stop Elimination? Quote: (Originally Posted by sensor330) What is your ascent rate? I called Kevin as I was having the same issue and he said that my ascent rate is to quick. Since than I've watched my ascent rate and haven't had any more long 10' stops. When I dive I usually dive with 2 computers a HH, and HS Explorer. I've found that the HSE and HH agree to with in 2 mins but I've also noticed that the time to surface does not match. Scott The first stop called for was at 30 feet. However, we were spending most of the time on the deck, averaging just over 100. So, I did a short stop at 60, 1 minute at 50, 1 minute at 40. I think that when I got to 30, instead of 3 @ 30 that was flashing originally, this went down to 2 @ 30. I can't remember now what it said for 20. I stayed at least what the hand set said and then probably some more. By this time, it was calling for either 1 or 2 minutes at 10. Remembering that it would take a while for it to clear the 10 foot stop if I go deeper, I moved up until there were divers above me on the anchor line. So, I could only get to about 12 or 13 feet. That's when it stayed on 1 @ 10 for the longest time. __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
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1st March 2006, 23:20	#17 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 2,075	Re: Hammerhead 10 Foot Stop Elimination? Quote: (Originally Posted by n2diving) One behavior some HH divers on the O2ptima have noticed is a final 1 min @ 10 fsw stop that does not clear for several minutes.... what we have found is wait the one minute by the clock, and then ease up to 9 or 8 feet and it will instantly clear. Ahaaa! In a way, I think that this is what happened. Finally, the divers above me on the anchor line surfaced. So, I moved up to 10. Waves passed overhead, and I bobbed up to 9 here and there. Poof! It cleared. I didn't associate clearing with that. I just thought I finally put in the time to clear it. So, does it only do this at the 10 foot stop? __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
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1st March 2006, 23:28	#18 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 2,075	Re: Hammerhead 10 Foot Stop Elimination? Gee, and I thought I was starting to remember the GF stuff. Because I went from U.S. Navy Tables straight to VPM, I never had more than an intellectual understanding of Buhlman related stuff over the years. Now, I have to start remembering how to apply it. How about this: Request for ability to set last stop depth made hereby. When can I send in my handset for the upgrade? __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
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2nd March 2006, 09:00	#19 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Home Build Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Home Build Join Date: Mar 2005 Location: "Da" Bronx Posts: 2,899	Re: Hammerhead 10 Foot Stop Elimination? Quote: (Originally Posted by UWSojourner) I don't think so. At least it shouldn't be done that way. Let's say you are at 20ft and your watch indicates you should stay at 20ft. Why does it keep you at 20ft? NOT because you haven't fallen below the 20ft GF, but because if you ascended to 10ft you would violate the 10ft GF. So, if you tell your watch that the last stop is 20ft, it should only clear if a direct ascent to the surface would not violate your HI GF. Remember we are talking about real time.. when you build tables, when a stop is clear (or your limits for that depth have been reached) it jumps to the next stop and the current gf is recalculated.. The current GF limit is based on the current depth.. The ascent is "clear" to the next stop based on the current GF limit.. when you clear a "stop" all it means is that upon reaching the next level you wount violate that limit.. __________________ Joe Radomski CCR Trimix Instructor Trainer ANDI Instructor Trainer Director #10 All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.
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2nd March 2006, 09:33	#20 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Home Build Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Home Build Join Date: Mar 2005 Location: "Da" Bronx Posts: 2,899	Re: Hammerhead 10 Foot Stop Elimination? Quote: (Originally Posted by ScubaDadMiami) Gee, and I thought I was starting to remember the GF stuff. Because I went from U.S. Navy Tables straight to VPM, I never had more than an intellectual understanding of Buhlman related stuff over the years. Now, I have to start remembering how to apply it. How about this: Request for ability to set last stop depth made hereby. When can I send in my handset for the upgrade? Here is the way I suggest you handle it.., after clearing the 20fsw stop, note the time it says you need to stop at 10fsw, once this period has cleared proceed to 10fsw, and it should be clear or at least damn close.. I know in metric mode it clears correctly when the depth displays 3msw, but there is a delay clearing when in imperial mode and you are at 10fsw or deeper.. I know all the calcs are done in MSW then displayed in fsw, following this logic 10fsw is actuactly the next stop depth (for a truncated integer), On an older revision (I havent tried it on the current sets) but I remember being at a "10 fsw" stop and just by moving my arm up and down to switch the display between 9 and 10 fsw I could get the 1 @10 to pop in and out.. __________________ Joe Radomski CCR Trimix Instructor Trainer ANDI Instructor Trainer Director #10 All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.
(Online)

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