Features of the Predator Dive Computer

The Predator is a full decompression dive computer incorporating the Bühlmann ZHL-16C algorithm, with user configurable Gradient Factors (GF). Gradient Factors allow the diver unique and individual control of their dive computer decompression calculations. An optional PIN upgrade to the Varying Permeability Model (VPM-B and VPM-B/GFS) decompression algorithm is now available. During a decompression dive, the Predator provides complete information displays of all required stop times. The Predator can provide time-to-surface based on "look ahead" at planned gas switches. Multiple gas definition presets are supported with any combination of oxygen, nitrogen and helium. The Predator will NOT "lockout" after a missed stop or ascent rate violation. Upgrade options also provide outstanding support for rebreathers.

Included with the Predator are two elastic straps with buckles, Fischer connector cover, USB Bluetooth adapter, and printed instructions for downloading software and users guide from the Shearwater Research website. The Predator also includes a screen protector already installed to help prevent scratches of the display face. The Predator SA model does not include the Fischer 103 connector.

The software includes a complete dive log manager, compatible with MS Windows. The dive log manager supports log downloads and firmware updates via the Bluetooth wireless interface of the Predator.

Upgrades for the Shearwater Predator

The VPM-B unlock code enables the option of using the Varying Permeability Model (VPM-B and VPM-B/GFS) algorithm for calculating decompression. The CCR unlock code upgrade adds several features to support rebreathers including the ability to perform constant PO2 set point calculations for deco. External PO2 monitoring adds the ability to continuously monitor up to three external O2 sensors, display an actual real-time FO2/PO2 of the inspired gas and use the information in deco calculations. Shearwater offers an oxygen sensor monitoring kit for the Kiss line of rebreathers. The Fischer 103 I/O port on the Predator is also plug compatible with oxygen sensor monitoring kits from other manufacturers for the O2ptima, Megalodon, rEvo, Inspiration, and Dräger rebreathers. The base PredatorSA stand alone model can be upgraded to CCR, but does NOT have the capability to be upgraded for external PO2 monitoring.

The Varying Permeability Model (VPM) is a decompression algorithm that attempts to predict the behavior of bubbles within the human body during decompression. Compared to typical Bühlmann profiles, VPM dive profiles often have deeper initial stops that are believed to reduce bubble formation, along with reduced time at shallow depths. VPM-B (a version that includes adjustments for Boyles Law effects) is popular among the technical diving community for use in calculating dive tables with required stops. The algorithm was initially developed by David Yount based on laboratory observations of bubbles under pressure and coded into Fortran by Erik Baker. Shearwater Research has implemented VPM-B according to the original Erik Baker Fortran specification. VPM-B allows a conservatism factor to be adjusted over a range of 0 (least conservative) to +5 (most conservative), the default is +3. In addition to implementing the Baker reference version, Shearwater Research has added an enhanced version because some divers believe the reduced shallow depth stop times may be too short for lengthy VPM-B profiles. The Gradient Factor Surfacing (GFS) option adds conservatism to the shallow stops on dives with significant decompression requirements (dives with total required deco exceeding an hour.) The GFS option is a hybrid that automatically chooses the decompression ceiling from the more conservative of the VPM-B profile and a Bühlmann ZHL-16C profile. For the Bühlmann profile a single gradient factor is used, adjustable over a range of 70% (most conservative) to 99% (least conservative), the default is 90%.

VPM-B, ZHL-16C, RGBM, VGM, VVAL-18M, DSAT... Does It Really Matter?

At the risk of annoying those who do have a preference for a specific decompression algorithm, the simple answer for most divers is NO the algorithm is not critical. There is no expert consensus that any one of the current crop of decompression algorithms is better than another. All of these algorithms used in dive computers and desktop table generation software, when set to their default conservancy values, will get you out of the water with an acceptable margin of safety. Among technical divers, the recent trend has been toward significantly deeper initial stops, based mostly on anecdotal reports within the community that some divers 'feel better' after such dives.

VVAL-18M is the basis for the modern US Navy Tables. Numerous variants of ZHL-16C are very widely implemented in both sport and technical dive computers. RGBM (basis for NAUI tables with it's roots in VPM) and DSAT (basis for PADI tables) are most often seen in no stop required sport diving applications. For technical diving, versions of ZHL-16C that include user selectable Gradient Factor modifications are very popular because the GF values can be used to generate deeper initial stops. VPM-B dive profiles typically also have deeper initial stops, along with reduced time at shallow depths resulting in a 'smoother' profile. Some divers believe the reduced shallow depth stop times may be too short for lengthy VPM-B profiles; the VPM-B/E and VPM-B/GFS variations exist to address this concern. VGM is a proprietary algorithm with deeper stops similar to VPM-B but with shallow stop times similar to ZHL-16C.

The most important safety factor is not the algorithm you select, rather that you follow very closely the recommendations of that algorithm and safe diving in general. Regardless of the decompression algorithm you use, it would be unwise to immediately surface once you have cleared your required decompression stop obligations. Doing so would result in your surfacing with the absolute maximum saturation allowed by the algorithm you selected, i.e. incurring the maximum risk. As with recreational NDL diving, after clearing your required decompression you should always perform an additional 3 to 5 minute 'safety stop' at your last stop depth.

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