From 6d679931d0626b829ae820c14d153206a766e104 Mon Sep 17 00:00:00 2001
From: Guillaume GARDET
Recreational mode is what comes closest to planning a dive based on the non-decompression limit (NDL). -It computes the maximum time a diver can stay at the current depth without needing mandatory decompression -stops and without using more than the existing gas (minus a reserve). The planner automatically takes -into account the nitrogen load incurred in previous dives. But conventional dive tables are also used in a -way that can take into account previous dives. Why use a dive planner for recreational dives? Using -recreational dive tables, the maximum depth of a dive is taken into account. But few dives are -done at a constant depth corresponding to the maximum depth (i.e. a "square" dive profile). This means -dive tables overestimate the nitrogen load incurred during previous dives. The Subsurface -dive planner calculates nitrogen load according to the real dive profiles of all uploaded previous dives, -in a similar way as dive computers calculate nitrogen load during a dive. This means that the diver gets credit, -in terms of nitrogen load, for not remaining at maximum depth during -previous dives, so a longer subsequent dive can be planned. - For the planner to work it’s crucial to upload all previous dives -onto Subsurface before doing dive planning. -To plan a dive, the appropriate settings need to be defined.
Recreational mode is intended for what most divers would call +"recreational", "sports"or "nontechnical" dives, remaining within no-deco +limits (NDL). It computes the maximum time a diver can stay at the current +depth without needing mandatory decompression stops and without using more +than the existing gas (minus a reserve). The planner automatically takes +into account the nitrogen load incurred in previous dives. But conventional +dive tables are also used in a way that can take into account previous +dives. Why use a dive planner for recreational dives? The subsurface dive +planner provides two significant advantages over the use of recreational +dive tables for dive planning.
Firstly, using recreational dive tables, the maximum depth of each previous +dive is taken into account. But few dives are done at a constant depth +corresponding to the maximum depth (i.e. a "square" dive profile). This +means dive tables overestimate the nitrogen load incurred during previous +dives. The Subsurface dive planner calculates nitrogen load according to +the real dive profiles of all uploaded previous dives, in a similar way as +dive computers calculate nitrogen load during a dive. This means that the +diver gets credit, in terms of nitrogen load, for not remaining at maximum +depth during previous dives, so a longer subsequent dive can be planned. +For the planner to work it’s therefore crucial to log previous dives in +Subsurface before doing dive planning.
Secondly, recreational dive tables are not designed to build additional +safety features into a dive. NDL times derived from dive tables often take +divers close to the limit where decompression sickness (DCS) can arise. The +Subsurface dive planner allows a diver to build more safety features into a +dive plan, preventing recreational divers from getting close to the limits +of getting a DCS hit. This is performed by specifying appropriate gradient +factors for a dive plan, as explained below.
To plan a dive, the appropriate settings need to be defined.
Ensure the date and time is set to that of the intended dive. This allows calculation of the nitrogen load incurred during previous dives.
+To build additional safety into the dive plan (over and above those of + recreational dive tables), specify gradient factors less than 100% (GFHigh + and GFLow under the Planning heading in the planner). On the other hand, + to approximate the values in recreational dive tables, set the gradient + factors to 100. By reducing the values of GFHigh and GFLow to values below + 100, one can build more safety into a dive. Decreasing the values of the + gradient factors below 100 will shorten the duration of the dive. This is + the price of a larger safety margin. Reasons for using gradient factors less + than 100 may be the age of the diver, the health of a diver, or unusual + conditions such as cold water or strong currents. Realistic conservative + values for the gradient factors are GFLow=40% and GFHigh=80%. This allows + you to create a cusom dive plan, suited to yourself as well as the dive + conditions. +
+Below is an image of a dive plan for a recreational dive at 30 meters with +gradient factors of 100. Because the no-deco limit (NDL) is 22 minutes, +there remains a significant amount of air in the cylinder at the end of the +dive.
The dive profile in the planner shows the maximum dive time within no-deco limits using the Bühlmann ZH-L16 algorithm and the gas and depth settings specified as described above. The Subsurface planner allows rapid assessment of dive duration as a function of dive depth, given the nitrogen load incurred during previous dives. The dive plan includes estimates of the amount of air/gas used, depending on the cylinder settings specified under -Available gases. If the initial cylinder pressure is set to 0, the dive +Available gases. If the start cylinder pressure is left blank, the dive duration shown is the true no-deco limit (NDL) without taking into account gas used during the dive. If the surface above the dive profile is RED it means that recreational dive limits are exceeded and either the dive duration or the dive depth needs to be reduced.
Below is an image of a dive plan for a recreational dive at 30 -meters. Although the no-deco limit (NDL) is 23 minutes, the duration of the -dive is limited by the amount of air in the cylinder.
Below is the same dive plan as above, but with a safety stop and reduced +gradient factors for a larger safety margin.
+For more information about Gradient factors, see the section on Gradient Factor Preference settings. +
+If the VPM-B model is selected, the Conservatism_level needs to be specified on a scale of 0 (least conservative) to 4 (most conservative). This model tends to give deco stops at deeper levels than the Bühlmann model and often @@ -5702,82 +5745,61 @@ utilisant du EAN50 et utilisant les réglages décrits ci-dessous.
Les détails du plan de plongée
On the bottom right of the dive planner, under Dive Plan Details, the -details of the dive plan are provided. These may be modified by checking any -of the options under the Notes section of the dive planner, immediately to -the left of the Dive Plan Details. If a Verbatim dive plan is requested, -a detailed sentence-level explanation of the dive plan is given. If any of -the management specifications have been exceeded during the planning, a -warning message is printed underneath the dive plan information.
On the bottom right panel of the dive planner, under Dive Plan Details, +the details of the dive plan are provided. These may be modified by checking +any of the options under the Notes section of the dive planner, +immediately to the left of the Dive Plan Details. If a Verbatim dive +plan is requested, a detailed sentence-level explanation of the dive plan +is given. If any of the management specifications have been exceeded during +the planning, a warning message is printed underneath the dive plan +information.
If the option Display segment duration is checked, then the duration of each depth level is indicated in the Dive Plan Details. This duration INCLUDES the transition time to get to that level. However, if the Display transition in deco option is checked, the transitions are shown separately from the segment durations at a particular level.
The planner has a check box Display plan variations. By checking this box, -the planner provides information about a dive that is a little deeper or -slightly longer than the planned dive. This is found near the top of the -Dive plan details where the dive duration is indicated. The information is -intended to be used if it is necessary to modify the ascent "on the fly" in -the case of unexpected deviations from the dive plan during the dive. -Checking this option creates a lot of additional computation, to such a -degree that the planner is slower than otherwise. The information is -typically given as:
Runtime: 53min + 0:52/m + 4:21/min
-This indicates:
Dive plan variations: The planner has a check box Display plan variations. By checking this box, the planner +provides information about a dive that is a little deeper or slightly +longer than the planned dive. This is found near the top of the Dive plan details +where the dive duration is indicated. The information is intended to be used if it is necessary to +modify the ascent "on the fly" in the case of unexpected deviations from the dive plan during the dive. +For example, if it says "Runtime: 123min, Stop times + 2:49 /m + 1:30 /min" this means: if you dive deeper +than planned, you should add almost 3 minutes per meter you go deeper to your decompression (and +you can substract 3 minutes per meter that you stay shallower). If you overstay your bottom +time, you need to add one and a half minutes to the stops for each minutes you overstay +and similarly, you can shorten your deco time by one and a half minute for each minute +you stay shorter. These variations of depth and time are based on the last manually entered segment of the +dive (not necessarily the deepest). The additional minutes should be distributed +over the differnent stops in a way proportional to the stop length, i.e. add more of the +additional minutes to the longer, shallower stops. The given times refer to the +duration of the decompression phase and do not include the extended bottom time! +This way of altering dive plans becomes inaccurate for large deviations from the original +plan. So it should not be trusted for more than a few minutes or meters of +deviations from the planned bottom time. Checking this option creates a lot of additional computation, +to such a degree that the planner is slower than otherwise.
Minimum gas requirements: The planner also estimates the minimum gas pressure +required for safe ascent after an event that causes the dive to be aborted. The +calculation assumes that in worst case an out of gas (OoG) +situation occurs at the end of the planned bottom time at maximum depth, requiring +additional time at maximum depth to solve the problem and forcing +the buddy pair the share the gas of one diver. In addition the combined SAC of both +divers is increased by an estimated factor compared to the SAC of a single diver under normal conditions. +The result of the minimum gas calculation for the bottom gas is printed to the planner output. There +are two selector boxes on the left of the Dive plan details:
-Calculated dive duration is 53 min. -
--For each extra meter in depth during the bottom phase of the dive, the - ascent duration increases by 52 seconds. +SAC factor. This is an estimate of the degree to which your SAC increases + if a critical problem arises underwater, e.g. gas sharing or + entanglement. Realistic values range from 3 to 5, reflecting the gas use of + two divers sharing a single gas cylinder after an OoG situation.
-For each extra minute of bottom time, the duration increases by 4 min 21 - sec. Thus, if the bottom time is two minutes longer than planned, ascent - duration duration will be (2 * 4min 21 sec) = 8 minutes 42 sec longer and - would probably require that each deco stop is 8:42/53:00 = around 16% longer - than planned. These calculations are only applicable for small deviations - from the dive plan, not for larger deviations. -
-Minimum gas requirements
The planner also estimates the minimum gas pressure required for safe -ascent after an event that causes the dive to be aborted. The calculation -assumes that in worst case an out of gas (OoG) situation occurs at the end -of the planned bottom time at maximum depth. This OoG event forces the buddy -team the share the gas of one diver and that they require an additional -period of time at maximum depth to solve the problem at hand. In addition -the combined SAC of both divers is increased by an estimated factor compared -to the SAC factor of a single diver under normal conditions. The result of -the minimum gas calculation for the bottom gas is printed to the planner -output. No automatic checks are performed based on this result. The feature -only gives valid results for simple, rectangular shaped single level dive -profiles. For multi level dives one would need to check every leg of the -profile independently.
There are two selector boxes on the left of the Dive plan details:
-SAC factor. This is an estimate of the degree to which your SAC increases if a critical problem arises underwater, - e.g. gas sharing or entanglement. Realistic values range from 2 to 5, reflecting the gas use of two divers sharing - a single gas cylinder after an OoG situation. -
--Problem solving time. This is an estimate of how long you would take to solve the problem before starting the ascent - to terminate the dive. The default value is 2 minutes. +Problem solving time. This is an estimate of how long you would take to + solve the problem before starting the ascent to terminate the dive. The + default value is 2 minutes.
-Within parentheses, the SAC factor and Problem solving time specified. +Within parentheses, the SAC factor and Problem solving time specified.
No automatic checks are performed based on this result. The feature only +gives valid results for simple, rectangular shaped single level dive +profiles. For multi level dives one would need to check every leg of the +profile independently.
Isobaric counterdiffusion information: For gas switches during the ascent in hypoxic open-circuit trimix dives information +about isobaric counterdiffusion (icd) is given near the bottom of the Dive plan details, based on the +rule-of-fifths (i.e. during a gas change, the increase in nitrogen partial pressure should not exceed +one fifth of the corresponding decrease in partial pressure of helium). For each gas change, two lines +are printed, indicating the changes in gas fractions (%) and the equivalent changes in partial pressures. If the +rule-of-fifths is not met, the relevant information is highlighted in red and a warning message appears +at the bottom of that table. The gas change events on the dive profile also provide information on icd, +visible at the bottom of the Information box when the mouse hovers on the respective gas change icon. This information +is only shown for gas changes relevant with respect to icd. If the rule-of-fifths is not met, +a red warning exclamation mark is shown over the gas change icon. When relevant, the Information box contains +information such as: ICD ΔHe:-13% ΔN₂+3%>2.6%. This means: for this gas change, the helium +decreased with 13% while the nitrogen increased with 3% which +is more than the 2.6% maximum increase in nitrogen suggested by the rule-of-fifths.