{Guest blog post by Bottom Times}
So, your new adventure has begun! You chose to invest time and money into a great sport and successfully completed your Open Water Scuba Diver certification! Congratulations…but now, what is the next logical step, or more to the point, the next logical place to invest your hard earned money? Although, I will always encourage new and seasoned divers alike to further their diving knowledge through continuing education, in my opinion, the next purchase that a newly certified diver should make after earning the initial certification is a dive computer. In later posts, I will break down the benefits to owning a full kit, but for an immediate return on investment, in my opinion, there is no better purchase than a dive computer!
Although many PADI instructors still teach the Open Water Scuba class with the Recreational Dive Planner (RDP), the option does exist, at the discretion of the instructor, to teach the class utilizing dive computers. While I do believe that all divers should have a basic understanding of the RDP, diving with a computer not only un-complicates the sport, it also provides the single greatest benefit of any piece of gear to a diver…it extends your dive times for deeper dives!
For those certified divers who were required to learn how to use the RDP during the Open Water course, you will remember that you can find your no decompression limit, or “no d limit” for a given depth by finding the depth in the upper left corner of Table 1 and following it down to the number in the black box. As you can see below, a dive with a maximum depth of 40 feet yields a no d limit of 140 minutes. A newly certified recreational diver would likely run low on air and end the dive long before the diver ever got close to the no d limit. In this case, diving with the RDP would likely not limit your dive time due to approaching a no d limit.
But, what if you quickly earned your Advanced Open Water and Deep Diver certifications and you want to dive on a reef that is at a depth of 116 feet? How would using the RDP affect your dive time versus using a dive computer?
When using the RDP, the dive profile is referred to as a “square profile”. This means that for any dive using the RDP, your maximum depth is also the depth for the entire dive. The RDP does not make allowances for shallower depths during the descent or the ascent.
Using the table below, you can see that diving on the reef at a depth or 116 feet would yield a no d limit of 13 minutes. Unlike the dive in the previous example, the limiting factor in this scenario for ending the dive would most certainly be the no d limit of 13 minutes.
Let’s look at the above example of a dive to 116 feet from an actual dive in Bonaire at Weber’s Joy using a dive computer. In the picture below, the numbers along the bottom of the profile indicate the time in minutes and the numbers on the left vertical portion of the profile indicate the depth in feet. As you can see, this particular dive was to a depth of 116 feet with a duration of 39 minutes with an average depth of 43 feet. At no point during this dive did I violate a recreation diving rule for depth or time. I was well within my no d limit, but if I plugged the numbers from this dive into the RDP table, I would have exceeded my no d limit by 26 minutes!
Because a dive computer is constantly calculating nitrogen loading based on depth, the dive does not adhere to the RDP square profile rules allowing a dive at a given depth using a computer to potentially be much longer than using the RDP. Remember, this is much more apparent for deeper dives where the RDP no d limit is the limiting factor.
Computers are simple to use, make logging dive much easier, and most importantly, as discussed in the examples above, extend dive times. They can cost anywhere from around 150 dollars up to a few thousand dollars, depending on what features you are looking for. Most dive computers are compatible with Enriched Air Nitrox as well, adding additional benefits for repetitive diving.
My wife and I dive the Shearwater Petrel 2 and the Liquivision Lynx. We both love the computers and would recommend either to anyone in the market. Because there are so many computers on the market taking the time to find the computer that best fit for your diving needs will ensure that your computer will remain part of your kit for years to come.