Ratio Deco Calculations
Ratio Deco is one of the most recent decompression algorithms that has become popular with "technical divers".
While Ratio Deco does indeed tend to quite closely follow many of the more "standard" decompression algorithms there does remain some concern and is not recognized ubiquitously among the diving community.
Given that ALL of the decompression algorithms have various "assumptions" and different tissue connectivity algorithms ... as well as several "user selectable adjustments" to these standardized models (e.g. adjustment for age and for conservativism vs. aggressive use of the models, etc.) Ratio Deco does indeed fall quite closely within other model domains.
What Ratio Deco does provide the technical diver is a "somewhat" simplified means of adjusting their deco assent "on the fly" as they vary from their original dive plan. For example, the diver may plan for a bottom time of 40 minutes and then cut short the bottom time dive to 30 or less. Also, Ratio Deco calculations are based on "average depth at bottom time". So if you planned a dive for 230 feet deep but were +/- above the bottom of 230 on a shipwreck moving from 230' to 210' you would compute your Ratio Deco stops using an "average depth" for your bottom time somewhere between 230 and 210. Many of the newer advanced dive computers now aid the diver by allowing them to "reset" the start of the "average" depth. This allows the tech diver to reset as he/she arrives on top of the shipwreck (or other "work area of bottom time" and the dive computer begins to average the depth for you until you begin your assent. It is this type of "on the fly" dive planning that attracts Ratio Deco as an alternative to the standard dive computer decompression models.
Below is an Excel spreadsheet which I wrote that can approximate the Ratio Deco calculations. You should be aware that if you research Ratio Deco you will find several "subtle" variations in the way in which it is actually calculated (albeit all are quite close in their final deco stop depths/time). The spreadsheet uses only one such methodology!!!!!!
While Ratio Deco does indeed tend to quite closely follow many of the more "standard" decompression algorithms there does remain some concern and is not recognized ubiquitously among the diving community.
Given that ALL of the decompression algorithms have various "assumptions" and different tissue connectivity algorithms ... as well as several "user selectable adjustments" to these standardized models (e.g. adjustment for age and for conservativism vs. aggressive use of the models, etc.) Ratio Deco does indeed fall quite closely within other model domains.
What Ratio Deco does provide the technical diver is a "somewhat" simplified means of adjusting their deco assent "on the fly" as they vary from their original dive plan. For example, the diver may plan for a bottom time of 40 minutes and then cut short the bottom time dive to 30 or less. Also, Ratio Deco calculations are based on "average depth at bottom time". So if you planned a dive for 230 feet deep but were +/- above the bottom of 230 on a shipwreck moving from 230' to 210' you would compute your Ratio Deco stops using an "average depth" for your bottom time somewhere between 230 and 210. Many of the newer advanced dive computers now aid the diver by allowing them to "reset" the start of the "average" depth. This allows the tech diver to reset as he/she arrives on top of the shipwreck (or other "work area of bottom time" and the dive computer begins to average the depth for you until you begin your assent. It is this type of "on the fly" dive planning that attracts Ratio Deco as an alternative to the standard dive computer decompression models.
Below is an Excel spreadsheet which I wrote that can approximate the Ratio Deco calculations. You should be aware that if you research Ratio Deco you will find several "subtle" variations in the way in which it is actually calculated (albeit all are quite close in their final deco stop depths/time). The spreadsheet uses only one such methodology!!!!!!
![](http://www.weebly.com/weebly/images/file_icons/xls.png)
ratio_deco_cals.xlsx |
Here are some samples from the Excel spreadsheet to show you the calculation results. Note that in Ratio Deco there are FOUR depth "regions" that are each computed differently. AND there are THREE types of computations that can "distribute" the depth/time stops for EACH REGION (LINEAR, EXPONENTIAL, "S"SHAPED ). In the examples below I used the "S" shaped depth/time distribution models, but the sheet also shows the exponential and linear methodology.
While this sounds complicated, once the diver decides on which method he/she wishes to use the "on the fly" calculations can be done during the dive with relative ease. Hint: use an arm slate or UW book to write down your depth/time stops ... you don't want to be "mentally re-computing them every time you get to a stop and forget "what was the time for this depth????"
What's the downside? Well ... there is always the chance of you suffering mild cases of nitrogen narcosis and struggle with the math. Speaking of which ... how's your mental math skills. Overcome these by at least having a WRITTEN DIVE PLAN with you if you plan to use Ratio Deco. Fall back and/or compare your Ratio Deco stops to your dive computer. Another good suggestion is to check with your Ratio Deco dive buddy on the longer/shallower stops where the times can vary more. Two heads are always better then one ... and you definitely have time to cross check as you're "hanging out" at a deco stop!!!!
While this sounds complicated, once the diver decides on which method he/she wishes to use the "on the fly" calculations can be done during the dive with relative ease. Hint: use an arm slate or UW book to write down your depth/time stops ... you don't want to be "mentally re-computing them every time you get to a stop and forget "what was the time for this depth????"
What's the downside? Well ... there is always the chance of you suffering mild cases of nitrogen narcosis and struggle with the math. Speaking of which ... how's your mental math skills. Overcome these by at least having a WRITTEN DIVE PLAN with you if you plan to use Ratio Deco. Fall back and/or compare your Ratio Deco stops to your dive computer. Another good suggestion is to check with your Ratio Deco dive buddy on the longer/shallower stops where the times can vary more. Two heads are always better then one ... and you definitely have time to cross check as you're "hanging out" at a deco stop!!!!