Ascending without a dive computer

[BRT]

I wonder if I can get my pressure pot to release the pressure slowly enough to simulate a deep dive with a slow ascent. Probably not, but I’ll try it.

Mine is fed by a pressure regulator. I can take it up in fairly small steps.

 

[EireDiver606]

I'd buy a bottom timer or a cheap computer, you can pick something up for around £100 and it'll save you alot of stress, from there is just basic math. Also...18m per minute is pretty quick, might wanna slow that down a notch fella.

Yeah 18m is PADIs standards even though in reality that is bloody quick. I think you’d have a hard time ascending quicker than that!

 

[EireDiver606]

A good analogy can be made for a car GPS system vs a map and a dive computer versus a bottom timer and tables.

Sure you could use a map, a ruler, and a pen when planning your next road trip, and draw lines on the map and estimate your travel time and arrival time, and you'd get there eventually and you could tell everyone that you don't need a fancy car GPS and people that use car GPS devices don't know what they're doing and feel they can't drive safely without a car GPS system but that would be a bit shortsighted. Because there's a lot more useful information in GPS devices that can make the trip easier, faster, more convenient, more pleasant, and yes, even safer.

The car GPS can calculate real time data on the fly, such as accidents, traffic, and construction delays and stop offs to take a piss or grab a bite to eat, and provide route alternatives while constantly recalculating and adjusting arrival times and mileage so that you know what time you'll arrive which can be rather useful especially when coordinating with other people or arriving at an event. A car GPS can also provide information such as where to find enroute gas stations, restaurants, strip joints, medical care, and other useful data.

You don't find too many people using maps and pens and rulers nowadays do we? For the same reason we don't find too many divers using bottom timers and tables. The technology we have available today is smart, accurate, easy to use, cheap and reliable- although on that last point there are occasionally technology failures- in which case a diver can protect him or herself by carrying a cheap backup computer.

Of course the analogy is not perfect, but it's close.

When comparing dive computers to bottom timers and tables, computers provide the following advantages that tables and bottom timers do not:

1- Even in the unlikely scenario that a diver follows their exact dive plan and doesn't deviate from it, there is no way a diver can calculate their exact depths and times and convert that to N or 02 absorption during a typical dive when they are constantly ascending and descending (even if it's only a few feet here or there), at best they have to round off several times, and they will almost always be forced to shorten their dive because they must use the more conservative, deeper depth calculations. A divers brain will never be a match for a computer- unless perhaps you've got autism like the dude in Rain Man- and even then it's going to be a lot of effort to constantly monitor your depth and time and recalculate on the fly.

2- Computers provide real time feedback and predict the dive time remaining at any particular moment based on calculations that can be derived from as many as 4 different factors including depth, time, 02 and N limitations.

3- Computers take a lot less time and effort and allow the diver to spend more time looking at the wreck or the pretty fish rather than screwing around with slates and performing calculations and remembering them while also trying to enjoy the dive itself.

4- Many computers store dive data (including gas consumption on air integrated models) and allow it to be downloaded to a dive log and create a profile showing times and depths during the dive which if nothing else is pretty cool compared to jotting some notes in a paper log book or manually entering basic data- at any rate its a huge time saver being able to simply pull the numbers off the computer into a digital log book and add a few notes.

5- Other important information is right there on the screen including temperature and time of day and ascent rate (the original topic of this thread).

There is not one valid reason to use dive tables and bottom timers over a dive computer other than perhaps for the sake of using vintage dive gear such as the guys who use early generation regulators and dive with no BCD because it's more "pure" or something of that nature.

The difference between that analogy and reality is that people do use bottom timers and use it to plan square profile dives. No one draws lines on maps to get to their destination, they simply read the map rather than listening to gps.

 

[EireDiver606]

Well you couldn't tell me that underwater because I wouldn't understand what you're saying.

Straw man argument.

Use wetnotes.

 

[J-Vo]

Using pure Buhlmann ZHL16c.

You can stay at 130 FFW for 9 minutes with no deco ceiling and ascend directly to the surface (infinity ascent rate) without breaking the M-value line.

Minimum ascent rate from this dive would be 2.8'/M without breaking the ceiling, but at about 100' you have an 11 FFW deco ceiling (green shadow below) showing more decompression stress from this ascent profile. I would need double AL80s to complete this profile.

@ 30'/M you can stay for 12 minutes before you ascent will break the ceiling.

Also, I wouldn't dive 99/99.
.

 

[Zef]

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

Until you decide to get a computer you can easily monitor your ascent time...while PADI recommends 18m/min most others in the industry have gone to 9m/min....at 9m/min you would be ascending just under 1meter every 6 seconds. So if you watch your depth gauge while ascending and count 1-1 thousand 2-1 thoundand and so on, at 6 you should have travelled approximately 1m. Repeat until you get to your safety stop and then hang for 3min and repeat again until you arrive at the surface.

As others have pointed out there are lots of good reasons to dive with computer but it is not absolutely necessary. And for single dives unless you are descending below 24meters you have plenty of dive time when using a table...24 meters has roughly 35min dive time according to the NAUI table....plus the 3min safety stop at 5 meters, plus a couple more minutes to ascend from the safety stop to the surface will give you 40 min total time from the time you descend to the time you break the surface (NAUI calculates dive time from the moment the diver begins to descend to the point they arrive at the safety stop, they do not include the time at the safety stop. PADI calculates dive time (actually bottom time) from the moment one begins their descent to the moment one begins their ascent to the safety/surface....PADI does not include ascent time or safety stop time in the dive time (bottom time) when planning a square profile)....I am an advocate of using a computer but most of my dives are within the range of depth and time mentioned above...my dive partners' air limits me to about that much time and my desire to be under the water is limited by the boredom factor...I usually am looking for a change of scenery at somewhere between 40-60 minutes....but then we are mostly diving lakes and quarries where I am located.

Things get a little more limiting when using a table to plan a dive below 24 meters especially as the depth equals or exceeds 30 meters....at that point or if you are going to do multiple dives per day it starts to make more sense to purchase a computer.

If you are only diving occasionally I can understand why you would not want to invest in a computer...don't sweat it....1 meter every 6 seconds should suit you fine until you do.

-Z

 

[txgoose]

This thread is going to be as unhealthy for my training budget as the DIY threads are for my vintage gear collection budget. It’ll be a couple of years and a lot more diving later but I can see that tech classes may be unavoidable. I could still ask a ton more questions but it would be even more unfair to the OP, and at some point I need some training to ingest this stuff better. And now jvogt is going to wreck my afternoon futzing with Subsurface!

 

[Diver0001]

(apologies if I snipped out relevant parts of your post) Can you explain this more? I am surprised that a person could have too slow an ascent rate. I understand that the tissues that on gas slower will off gas slower. But it seems like a _very_ slow ascent rate, with enough air (not tech gassing), should actually have a person reach the surface in equilibrium. And maybe this is more a discussion of the applicable sweet spot, vs my theoretical and admittedly impractical sweet spot. Anyway, a neat area of thought possibly better suited for a separate thread.

Sorry for the late response, I haven't been following this thread very closely.

The crux of the issue is that the underlying decompression model contains 16 theoretical "compartments".

All of those compartments are either on-gassing or off-gassing depending on depth at any given moment during the dive. The only time that all 16 compartments are off-gassing at the same time is when your depth is 6m or less. Hence the reason why the safety stop is set at 5m.

During the dive only one compartment will be "closest" to the NDL. What your computers shows you is the numbers for THAT compartment and only that compartment. As the dive progresses a different compartment could become controlling and the computer will show you those numbers instead.

So what happens during any ascent, no matter what the speed, some compartments will begin to off-gass while other compartments are still on-gassing, even during the ascent.

The issue that you can run up against is that it's the "slower" compartments that continue to on-gass during an ascent and generally speaking it's the slower compartment that are implicated in decompression sickness. So to a certain extent, the slower your ascent is, the more you load up the very compartments that you DON'T want to be loading up unnecessarily.

There have been some very good (albeit at times heated) discussions on Scubaboard about the relative inefficiencies of bubble models for decompression diving. What a bubble model does is essentially slow your ascent speed down (under some conditions by quite a lot) and what research has shown is that the resulting over-loading (to give it a term) of the slower tissues is directly linked to a higher instance of decompression sickness.

Do a search on the word NEDU and you'll probably find some of those threads.

I should say, before you read too much about it, that the NEDU research is exceedingly relevant to technical divers but for recreational divers, if you use a computer, stay within the NDL's and do a safety stop at the end of the dive, this effect is still present but unlikely to result in you getting sick from it.

R..

 

[agadiver78]

n/t

 

[TMHeimer]

Before I got my computer I used watch and gauge and did the 60' per minute thing by doing 10' every 10 seconds--I found that easiest. Even PADI now basically recommends 30' per minute so I guess that would be 5' every 10 seconds. Until those parameters change again.