Ascending without a dive computer
- Thread starter Chris Richardson
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Bob DBF
Contributor
That would be a deco dive, as the rec diver doing that profile would not have direct access to the surface for most of the dive. The ascent would have to be faster than 2.8'/min to avoid a deco ceiling during the dive.
If deco diving, you can go as slow as you have the gas to complete the deco obligation you incur.
Bob
I am still learning the tool, but the lowest I could come up with in Subsurface, using their recreational config was 11ft/min. For something akin to a max rec dive, anyway. As discussed before, when you’re deep do your thing then get gone. Once you are shallower, the ability to dilly dally grows considerably. 10ft/min produced a deco ceiling below 75% ave depth, as did 2ft/min for the 75%-50% ave depth parameter. Three minutes at depth also produced a deco ceiling. It required an 18ft/min ascent rate to remove the ceiling.
J-Vo
Contributor
Bob DBF
Contributor
The issue that I can see is that ascent rate probably will not hold up if you you do the full 10 min of NDL time at 130'. In order for it to be the slowest ascent rate for recreational divers, it has to work on the entire table not just on a specific case. A deco ceiling at any time is incompatible with NDL diving, and the gas planning needed deserves a note.
Bob
I don’t disagree with the gas planning note. But the image does show negative gas remaining and a warning in red. At some point a 1ft/min ascent rate shown at shallower depths is probably not very feasible, I was simply trying to max out the discussed min ascent rate. 11ft/min is what I’m seeing. I was trying to be under the five minutes indicated on the SSI tables I have. If other tables show 10 minutes max bottom time, the results would be different. The five minutes recommended by SSI seems to be borne out by the Subsurface program as well. Once you go to a sixth minute you have to ascend at 36ft/min to remove a deco ceiling. At seven minutes you can’t remove the deco ceiling by ascent rate.
Five minutes was all I could do to keep the deco ceiling from appearing and staying below 30ft/min ascent rate. If we aren’t just pressing hard against NDL, the four minutes I used seems reasonable. For five minutes, the min ascent rate shows to be 17ft/min. As a “rule of thumb” this is probably a closer approximation. Add in some room for error, say 20ft/min. I am a bit surprised that this isn’t stressed more in deep dive specialties. Maybe it is and I missed it, or maybe it is by other agencies. A 10ft/min window is relatively narrow. Still goes back to something like “Get deep, get your stuff done, get gone.”
Bob DBF
Contributor
I think that some people get hung up on the ascent rate no faster than xx'/min rather than looking at it as the specified ascent rate for the algorithm. Yes you can go slower, however you have to be carefull where you do it, some places like safety stop may be fine, and other places like 120' are not so good.
Way back when I learned to dive deep, my mentor was a fan of "Get deep, get your stuff done, get gone". He believed that when anything went wrong, deeper was not better, and the longer you hung around the longer the deco, assuming you brought enough air.
Bob
NAUI Wowie
Contributor
Hi guys
With sadly being only an occasional scuba diving the extent of my information equipment is only a Citizen Promaster Diver AY5000-05L, instrument console depth gauge and a PADI eRDP. As a result, without owning a dive computer, gauging a safe ascent rate of 18m/30ft per minute accurately is pretty hard without having some sort of visual indicator of depth other than the depth gauge on your instrument module/console. So with this in mind is the "never ascend faster than your smallest bubbles" adage a safe rule to live by? Swimming up with slightly negative buoyancy to better control your ascent rate is a safe method to use but a visual comparison by way of the bubbles is surely an immediate reference rather than trying to gauge the 18m/30ft per minute (equating to 1.5m/5s or 2.5ft/5s which is probably easier to estimate?) rate? Any thoughts, opinions, recommendations, etc, about this would be appreciated. Many thanks
I did my 4 OW dives 14 months ago with a diving watch and spg compass standard. No computer. I knew how long I was underwater and when to tell my instructor id been under exactly 20 minutes. It was cool the instructor got a kick out of it and made sure i knew how to use it correctly and the old style compass and all. So no you dont need a dive computer you can know exactly how long your dive is and was. The only thing you may not know is your max depth you achieved if you are not paying attention.
Now most of us use diving computers with built in compasses and water temp, nitrogen level buildup etc. But its all common sense. watch your remaining air, depth, and go way slower than your bubbles up to surface.
If you ever get into a zero visibility situation though having a nice bright dive computer is a HUGE HUGE help. Ive got only 31 dives and its already happened to me. Dive watch is about useless in that situation and when i went zero viz id not been expecting that before the trip. You never know.
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