Background
This article is about a “feature” in the Shearwater diver computer that I believe most people are unaware of and that is not really documented in the user manual. It is about the “Dive Plan” feature which divers probably most often use to plan a dive before they enter the water; however, it is also available during a dive and has quite a few interesting features.
I’ve been maintaining a list of desired features in the Shearwater dive computers I use on every dive. Some of them have actually been implemented which is cool. I’m not sure if it was my input or others or both, but it is nice that Shearwater continues to add new software features including the ability to see your deco plan during a dive.
During a recent dive trip, I was discussing my desire to have the “Bailout TTS” feature and a fellow diver said that it “kind of exists” but you have to go through a few button pushes to get it.
I would still like a single number to be displayed similar to @+5 or SurfGF for the Bailout TTS, but Shearwater has added new features to the “Dive Plan” display during a dive.
Forgive the pictures, I was alone on a dive and couldn’t get somebody to help me photograph my computer so I had to use my GoPro and get some photos and frame captures from a movie.
The “Live” Dive Plan
If, during a dive, you use the left button a few times, you will get to Dive Setup and then Dive Planner (as detailed in my post above).
In fact, in the post, I postulated that the “Next” button might reveal more including a bailout plan. I apparently was correct. It has taken some prodding from a fellow diver and a couple years to explore and document it.
Below is the sequence of events that happen when you select “Dive Planner” during a dive in Closed Circuit mode.
Step 1 – Closed Circuit (CC) Deco Ascent Plan
This will show your deco schedule and total runtime (53 minutes in this case).
Note: It shows a PO2 of 0.5 because I change my Set Point from Hi to Lo right before my ascent starts and then manually control my PO2. The deco plan is calculated based upon the actual PO2 at the time and not the set point.
It also shows your current depth (92 feet), the current run time (18 minutes) and the running total of the runtime at each deco stop. The first push of the “Next” button shows the rest of the deco schedule while running in closed circuit mode (assuming it doesn’t fit on one screen).
Step 2 – Closed Circuit Dive Summary
If you select “Next” again, it will show a summary of the dive in closed circuit mode assuming you do all the required deco stops at the perfect depth, etc. It shows the calculated total runtime (53 minutes), the total amount of time of deco assuming you do all the stops at the exact depth (35 minutes).
Note that it also shows your ending CNS which could be useful for those who “care” about CNS and do long dives (not that I think anybody would cut deco short due to a high CNS value).
Step 3 – Bailout Planner
If you then select “Plan BO” you are presented with a similar deco schedule but now assuming that you have bailed out. It will show each deco stop, the gas switch, the time and the running run time. If more than one page is required, the “Next” button will take you to the rest of the deco schedule.
To me, the most interesting (or important) number would be the Time To Surface in Bailout Mode.
In this case, it would be about 19 minutes (8 minutes at 10′, 4 minutes at 20′, 3 minutes at 40′, etc. is a cumulative total of 19 minutes). This will, of course, change throughout the dive on the bottom or during deco and is what I refer to as “Bailout TTS.”
That is the one number I would like to be able to access and monitor in realtime (similar to @+5) without going through several screens. The reason is that the amount of bailout gas you bring on a dive is usually the limiting factor of the dive duration — it is usually not the rebreather scrubber or the amount of oxygen.
Step 4 – Bailout Gas Usage
Using the “Next” button will take you to a summary of your gas usage. This is, obviously, very useful given my comment above about the quantity of bailout gas being the limiting factor on most rebreather dives.
Also note that it lists the RMV as 0.5. cubic-feet-per-minute which is require to calculate your gas usage. I’ve heard that you can set your RMV (which would make sense) but I haven’t found out how to do that yet.
It would be really useful if you could configure your RMV when you are on deep bailout (it is usually higher) and a separate RMV for the “deco” portion of your dive. Most dive planning software programs allow you to do that.
Step 5 – Bailout Summary
I didn’t get a good picture of this, but the last screen shows a summary of the dive if you do bailout (total run time, total time on deco, ending CNS, etc.).
Summary
Shearwater continues to add useful features to the software for their computers. The Deco Plan and Bailout Plan while on a dive are good examples of that. As far as I know, they aren’t really documented in detail anywhere.
I still wish they would add the “Bailout TTS” to their list of information fields that can be displayed “real time” on the “home screen” while diving similar to SurfGF, Ceiling, GF99, etc.