Purpose
This model is intended to compare the cost of diving with a Closed Circuit Rebreather (CCR) versus diving with standard Open Circuit (OC) diving equipment over a configurable number of dives.
Philosophy of the Model
The cost of diving in each model is primarily dependent on the type of gas used in each system. The model primarily focuses on CCR costs and compares them with the cost of diving OC with both Trimix and Air/Nitrox across the specified number of dives. From the CCR perspective, the model can be configured to use either Trimix or Air/Nitrox as the diluent. Thus, the scenarios that can be addressed are:
- CCR with Air Diluent cost versus OC Trimix Costs and OC Air/Nitrox costs
- CCR with Trimix Diluent cost versus OC Trimix Costs and OC Air/Nitrox costs
Features
- Ability to specify Trimix or Air/Nitrox as the CCR diluent
- Support for oxygen deco cylinder usage for both CCR and OC
- Configurable Trimix cost per cubic foot of helium and oxygen used, or flat fee pricing for banked trimix
- Configurable Oxygen cost per cubic foot, or flat fee per fill
- Flat-fee cost per cylinder fill for Air/Nitrox
- Support for CCR absorbent costs over the specified dive periods, given relevant inputs
- Ability to specify the percentage of OC backgas consumed each dive (used to determine gas volume required for subsequent dives)
- Ability to specify CCR “sunk costs” (e.g., training, cost of unit) as well as recurrent maintenance costs over the dive period (recommend unit maintenance, oxygen sensors)
- Calculation of cost savings benefits of using CCR (if applicable) on a per-dive basis or over the course of the specified number of dives
- Calculation of the number of dives to recoup CCR investment based on sunk costs provided and ongoing cost savings
Limitations
- The model compares the scenarios described above, but it’s noted that your personal dive scenario may change over time. For example, you may be diving Air Diluent for 20 dives, then 21/35 Trimix over the next 25 dives, then 18/45 trimix over 5 dives, and you may be topping up with air somewhere in between. The model doesn’t support this type of mixed use. However, you could calculate each of these scenarios separately.
- Things get more complex if you’re diving hypoxic blends and need many different gas types. I’m not a hypoxic trimix diver, and I haven’t considered any of those scenarios.
- Right now, the display aspect is very US-specific in regards to units, mainly cubic feet and dollars. However, there is nothing specific in the model logic related to these units, so you can substitute in any currency you’d like, or use liters instead of cubic feet.
Directions
- Simply fill in the model input in the “Inputs” section of the form (or “Inputs” worksheet if you are using the Excel/Google Sheets version). The results are displayed to the right and updated in real-time. (If you’re using the Excel/Google Sheets version, results will be displayed in the two worksheet tabs for OC Trimix vs. CCR and OC Nitrox vs. CCR). The CCR diluent type is shown in red at the top of each summary tab as a reminder.
Questions or Suggestions?
Model developed by Chris Uriarte (chrisjur@cju.com)