Hammerhead 10 Foot Stop Elimination?

***ScubaDadMiami*** · 1st March 2006, 17:31

Due to my prior dive habits and preferences, I prefer to pull my last deco stop at 20 feet, not 10 feet. Then, I take about five or six minutes to go from 20 feet to the surface after the completion of this 20 foot stop. I don't like the last stop being at 10 because this can allow for unacceptably large depth changes in rougher seas when waves pass overhead, and it can get pretty rough at this depth as compared to making the last stop at 20 feet.

With my Hammerhead, it keeps calling for 10 foot stops. Even if I pull longer stops at 20, my required 10 foot stop time does not seem get reduced on the handset. Does anyone have a solution for this? What are you doing?

It would be great if the user could set the last stop depth on the unit.

***jradomski*** · 1st March 2006, 17:50

Quote: (Originally Posted by ScubaDadMiami)

Due to my prior dive habits and preferences, I prefer to pull my last deco stop at 20 feet, not 10 feet. Then, I take about five or six minutes to go from 20 feet to the surface after the completion of this 20 foot stop. I don't like the last stop being at 10 because this can allow for unacceptably large depth changes in rougher seas when waves pass overhead, and it can get pretty rough at this depth as compared to making the last stop at 20 feet.

With my Hammerhead, it keeps calling for 10 foot stops. Even if I pull longer stops at 20, my required 10 foot stop time does not seem get reduced on the handset. Does anyone have a solution for this? What are you doing?

It would be great if the user could set the last stop depth on the unit.

The HH will clear 10fsw stops at 20 fsw no problems, its just longer than you expect (its the way the HH projects the ascent).. If you run the math, on a gf profile with the endpoint being 10fsw, it requires a longer than the 10fsw listed to clear because of the difference in the way the allowable gf is calculaed (its based on current depth) (and loop content).. The lower the po2 is at 20fsw the longer it will take to clear.. if you keep the po2 at 20fsw between 1.4 and 1.5 it clears reasonably well., better yet.. after you clear your 20fsw time, just ascend a few feet (say to 15-18 fsw) the time will count off more quickly than if you were at 20-22fsw (again its how it predicts the ascent, the key is to above the previous stop depth (in meters))..

The higher you have the conservatism set (lower the gf-high) th slower you will see the time tick off..

***ScubaDadMiami*** · 1st March 2006, 18:40

I have the GF high at 90 (35/90), and it seemed like well above 5 minutes, more like closer to 10 minutes, to clear when I was just under 10 feet, say 12 feet (due to other divers being just above me on the line in strong enough current that I didn't want to drift free), saying 1 @ 10 for the longest time.

I don't want to raise the GF high more than this. Is that what would cure it: raising the GF high?

***jradomski*** · 1st March 2006, 19:05

Quote: (Originally Posted by ScubaDadMiami)

I have the GF high at 90 (35/90), and it seemed like well above 5 minutes, more like closer to 10 minutes, to clear when I was just under 10 feet, say 12 feet (due to other divers being just above me on the line in strong enough current that I didn't want to drift free), saying 1 @ 10 for the longest time.

I don't want to raise the GF high more than this. Is that what would cure it: raising the GF high?

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..

sensor330 · 1st March 2006, 19:07

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

***jradomski*** · 1st March 2006, 19:10

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 way the hh calculates an ascent is an overprediction of TTS due to rounding up and other factors, as you get closer to the surface the TTS numbers should get closer..

n2diving · 1st March 2006, 20:06

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.

sensor330 · 1st March 2006, 20:19

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.

Like I said I dive with 2 computers and when my HH says 10' for 1 min my other computer usally has several mins left. About 1 min before my HSE clears my HH clears, for those few mins my HH says I have 1 min at 10' and I do my last stop at 15'.

Scott

Genesis · 1st March 2006, 20:21

This is interesting.....

There is no difference between TTS from 20' to surface if you are at 100% FO2 inspired irrespective of whether you do the whole thing at 20', do some of it at 20' and 10', or do a "continuous deco" ascent to the surface.

The offgassing rate of inert gas(es) from your body is exactly identical, because the inspired amount of inert gas is zero.

The pressure gradient to ambient has nothing to do with offgassing rate - that is controlled by the gradient between F(inert) inspired : F(inert) tissue. If F(inert)inspired is zero, you cannot drive the offgassing any faster.

Your minimum safe depth is controlled by the overpressure in your tissues, but not the rate of offgassing. Of course there's a fairly significant difference in CNS clock accumulation between 20' and 10' though at 100% FiO2.....

Is there transparency of any sort in the HH's deco algorythm? This is one of the issues that I've run across with various decompression strategies - too many are "black boxes" with little or documentation on how they work, and when you see things like this it makes you wonder exactly what its doing in the code....

**UWSojourner** · 1st March 2006, 20:59

Quote: (Originally Posted by Genesis)

The pressure gradient to ambient has nothing to do with offgassing rate - that is controlled by the gradient between F(inert) inspired : F(inert) tissue. If F(inert)inspired is zero, you cannot drive the offgassing any faster.

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.

1st March 2006, 17:31	#1 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 1,927	Hammerhead 10 Foot Stop Elimination? Due to my prior dive habits and preferences, I prefer to pull my last deco stop at 20 feet, not 10 feet. Then, I take about five or six minutes to go from 20 feet to the surface after the completion of this 20 foot stop. I don't like the last stop being at 10 because this can allow for unacceptably large depth changes in rougher seas when waves pass overhead, and it can get pretty rough at this depth as compared to making the last stop at 20 feet. With my Hammerhead, it keeps calling for 10 foot stops. Even if I pull longer stops at 20, my required 10 foot stop time does not seem get reduced on the handset. Does anyone have a solution for this? What are you doing? It would be great if the user could set the last stop depth on the unit. __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
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1st March 2006, 17:50	#2 (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: 2,817	Re: Hammerhead 10 Foot Stop Elimination? Quote: (Originally Posted by ScubaDadMiami) Due to my prior dive habits and preferences, I prefer to pull my last deco stop at 20 feet, not 10 feet. Then, I take about five or six minutes to go from 20 feet to the surface after the completion of this 20 foot stop. I don't like the last stop being at 10 because this can allow for unacceptably large depth changes in rougher seas when waves pass overhead, and it can get pretty rough at this depth as compared to making the last stop at 20 feet. With my Hammerhead, it keeps calling for 10 foot stops. Even if I pull longer stops at 20, my required 10 foot stop time does not seem get reduced on the handset. Does anyone have a solution for this? What are you doing? It would be great if the user could set the last stop depth on the unit. The HH will clear 10fsw stops at 20 fsw no problems, its just longer than you expect (its the way the HH projects the ascent).. If you run the math, on a gf profile with the endpoint being 10fsw, it requires a longer than the 10fsw listed to clear because of the difference in the way the allowable gf is calculaed (its based on current depth) (and loop content).. The lower the po2 is at 20fsw the longer it will take to clear.. if you keep the po2 at 20fsw between 1.4 and 1.5 it clears reasonably well., better yet.. after you clear your 20fsw time, just ascend a few feet (say to 15-18 fsw) the time will count off more quickly than if you were at 20-22fsw (again its how it predicts the ascent, the key is to above the previous stop depth (in meters)).. The higher you have the conservatism set (lower the gf-high) th slower you will see the time tick off.. __________________ 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 17:56.
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1st March 2006, 18:40	#3 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 1,927	Re: Hammerhead 10 Foot Stop Elimination? I have the GF high at 90 (35/90), and it seemed like well above 5 minutes, more like closer to 10 minutes, to clear when I was just under 10 feet, say 12 feet (due to other divers being just above me on the line in strong enough current that I didn't want to drift free), saying 1 @ 10 for the longest time. I don't want to raise the GF high more than this. Is that what would cure it: raising the GF high? __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
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1st March 2006, 19:05	#4 (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: 2,817	Re: Hammerhead 10 Foot Stop Elimination? Quote: (Originally Posted by ScubaDadMiami) I have the GF high at 90 (35/90), and it seemed like well above 5 minutes, more like closer to 10 minutes, to clear when I was just under 10 feet, say 12 feet (due to other divers being just above me on the line in strong enough current that I didn't want to drift free), saying 1 @ 10 for the longest time. I don't want to raise the GF high more than this. Is that what would cure it: raising the GF high? 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.. __________________ 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 19:08.
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1st March 2006, 19:07	#5 (permalink)
sensor330 Custom Title Allowed! Current Rebreather/s: Megalodon Other Rebreather/s: Not Bought Yet Inspiration Classic Join Date: Feb 2005 Location: Victoria, British Columbia, Canada Posts: 549	Re: Hammerhead 10 Foot Stop Elimination? 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
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1st March 2006, 19:10	#6 (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: 2,817	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 way the hh calculates an ascent is an overprediction of TTS due to rounding up and other factors, as you get closer to the surface the TTS numbers should get closer.. __________________ 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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1st March 2006, 20:06	#7 (permalink)
n2diving Custom Title Allowed! Current Rebreather/s: Optima Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Feb 2005 Location: Florida, USA Posts: 270	Re: Hammerhead 10 Foot Stop Elimination? 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.
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1st March 2006, 20:19	#8 (permalink)
sensor330 Custom Title Allowed! Current Rebreather/s: Megalodon Other Rebreather/s: Not Bought Yet Inspiration Classic Join Date: Feb 2005 Location: Victoria, British Columbia, Canada Posts: 549	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. Like I said I dive with 2 computers and when my HH says 10' for 1 min my other computer usally has several mins left. About 1 min before my HSE clears my HH clears, for those few mins my HH says I have 1 min at 10' and I do my last stop at 15'. Scott
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1st March 2006, 20:21	#9 (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? This is interesting..... There is no difference between TTS from 20' to surface if you are at 100% FO2 inspired irrespective of whether you do the whole thing at 20', do some of it at 20' and 10', or do a "continuous deco" ascent to the surface. The offgassing rate of inert gas(es) from your body is exactly identical, because the inspired amount of inert gas is zero. The pressure gradient to ambient has nothing to do with offgassing rate - that is controlled by the gradient between F(inert) inspired : F(inert) tissue. If F(inert)inspired is zero, you cannot drive the offgassing any faster. Your minimum safe depth is controlled by the overpressure in your tissues, but not the rate of offgassing. Of course there's a fairly significant difference in CNS clock accumulation between 20' and 10' though at 100% FiO2..... Is there transparency of any sort in the HH's deco algorythm? This is one of the issues that I've run across with various decompression strategies - too many are "black boxes" with little or documentation on how they work, and when you see things like this it makes you wonder exactly what its doing in the code.... __________________ "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, 20:59	#10 (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 Genesis) The pressure gradient to ambient has nothing to do with offgassing rate - that is controlled by the gradient between F(inert) inspired : F(inert) tissue. If F(inert)inspired is zero, you cannot drive the offgassing any faster. 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.
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