A hybrid model runs Bühlmann ZHL-16C and Thalmann E-L on the same dive at the same time and resolves their two disagreeing ceilings into one schedule. DiveLogic offers two ways of doing that: Hybrid OC, which always takes the deeper ceiling, and DiveLogic Frontier, which produces a family of schedules and shows the trade between them. Both use a Thalmann parameter set, so read the Thalmann page before reading a number off either.
Hybrid OC: the deeper ceiling
At every step both models work out a ceiling, and the binding one is the deeper of the two. The ascent then follows the rule the single models use: hold at each stop until the binding ceiling clears the depth above, then go up. Where the models agree the result is identical to either alone; where they disagree the more conservative one wins, and you pay for the disagreement in runtime. The Bühlmann weight control does not change the ceiling, only the weighting of the two models in the risk figure the mode reports.
A hybrid plan reports how far apart the models were: the maximum disagreement between the two ceilings at any stop, the mean disagreement across the stops weighted by how long each lasted, and the fraction of decompression time each model was binding. When the maximum passes 6 m the plan carries a warning naming the figure and suggesting a more conservative schedule; that check is on by default and can be turned off in the hybrid settings. A large disagreement is information about the models rather than about the water.
The plan draws that gap directly. Where the trace sits away from zero the two models wanted different ceilings, and the deeper of them is the one you dived.
Decompression stops
| Depth | Duration | Gas | Bühlmann ceiling | Thalmann ceiling | Controlling |
|---|---|---|---|---|---|
| 15 m | 2 min | 50% | 13.2m → 11.2m | 9.1m → 7.7m | BHL |
| 12 m | 6 min | 50% | 11.2m → 7.5m | 7.7m → 4.3m | BHL |
| 9 m | 6 min | 50% | 7.5m → 5.3m | 4.3m → 2.5m | BHL |
| 6 m | 47 min | 50% | 5.3m → 0.0m | 2.5m → 0.0m | BHL |
If no schedule reaches the surface, because there are no usable gases or the profile is one nothing can clear, the planner falls back to a plain Bühlmann ZHL-16C plan and adds a warning saying so. What you are then looking at is not a hybrid schedule, and that warning is the only thing that tells you.
Frontier: a family of schedules
Frontier produces several schedules rather than one, each trading decompression time against accumulated oversaturation at a different rate, from the shortest ascent the gases permit to a markedly longer and gentler one. They are sorted by runtime and named Fast (the shortest), Balanced (nearest the midpoint), Robust (the one the two models argue about least, which is not the safest) and Conservative (the longest).
The plan you get is the Balanced schedule. The others are shown in the Hybrid Analysis view, so if you want the Conservative one you read it off that view yourself. Seeing fewer than four is normal, because several trades land on the same answer and duplicates are dropped. Each search also has a time budget and returns what it has when it runs out, which is why the analysis view can look sparse without the plan ceasing to be a hybrid plan.
The risk figures Frontier reports order the schedules against each other. They are not a probability of decompression sickness, and nothing in DiveLogic produces one.
What a hybrid does not give you
Combining two models does not average out their errors. Both are dissolved-gas models fitted to different trial data, and where they share an assumption, no bubbles, no diver-specific physiology, no thermal or exertion term, the hybrid shares it too. Taking the deeper ceiling makes the schedule longer than either model asked for. It does not make it right.
Next
- Thalmann E-L is the model on the other half of every hybrid.
- Reviewing a plan shows where the Hybrid Analysis view sits.