On a recent dive, I had an ad hoc dive buddy ask if we could do our second dive as a negative entry descent. A negative entry descent also called a negative buoyancy descent, is sometimes done when the surface conditions are very rough or when there is a strong current at the surface. There was no need to do such an entry on our dive, however, he explained that the following week he was diving a location known for fast surface currents. Information about the dive site indicated that a fast descent was needed. The key difference between a negative entry and a normal one is that there is no air in the BCD. Adding additional weights is not the means to become negative on these entries.
You strive to be neutrally buoyant at the end of your dive. To do this you need to add weighs to counter the weight of the air that you will use. To float at the surface before starting to dive, you need to add air to your BCD to counter that additional weighs so that you become positively buoyant when you enter the water. Without the air, you will sink.
Why Would You Do An Negative Entry Descent
Diving conditions may indicate that a direct descent is the only practical and safe method to make the dive. High seas may make it very uncomfortable even dangerous to hold on to a current line while everyone gathers to begin the dive. A strong current may take the dive boat and those on the surface away from the dive site. Those same conditions may be a hazard to the dive boat who will have to be without steerage while dives are around the boat. Coordination is a key factor. Dive buddies need to enter the water at the same time and close to each other. All divers need to be in the water as soon as possible to keep the group close.
I have seen these types of entries compared to base jumping. Once you are on the way down you control your position and glide path to land on your target. Here are some steps to consider.
- Site Brief/Dive Brief: While briefings are always important, briefings for these entries can be critical. It should include why you are doing the entry. If you are doing the entry because of rough seas or surface current, the instructions may tell you to level off and become neutral buoyant at a specified depth and then continue as a group. If the current extends well below the surface, you might drop directly to the dive site without a pause. The brief should also familiarize you with the intended actions of the boat before the entry phase, during the active entry, during the dive and pick up procedures.
- Equipment Check: Many times when I start a dive, I have some difficulties starting my descent. The reason is trapped air pockets in my BCD and wet suit. After you check that your BCD is fully functional, the inflator and dump valves are properly working, you need to remove all the air from your BCD. Squeezing the air out before putting it on is best. Not all wet suits are a perfect fit. Even a great fitting one may still have places where an air pocket can develop, one that might not immediately clear. I often get an air pocket in the small of my back and the side of my chest near my arms. It does not add much buoyancy, but I can tell when it been released. If you have a similar experience, try to remove air pockets in your wet suit. Make sure the buddy checks are complete.
- Final prep: On a dive with a normal entry, it generally okay to take an extra few seconds to get into the water. These types of entries will want the divers in the water in the shortest amount of time possible. If each diver takes an additional 10 seconds to enter the water, the dive group could easily be spread out over a large area. So it is important that you are ready to immediately enter the water when the dive starts. It is also important that we minimize any in water equipment adjustments. On a normal dive, we have time to make any last minute adjustments while in the water before starting our descent. For myself, I have a BCD that has a cummerbund. I always need to tighten it when I start a dive. On these dives do everything you can before the dive starts, any adjustments while free-falling can become a distraction from a safe dive.
- Entry: During the dive brief, you will be informed on how and when you enter the water. Both the giant step and back rolls can be used depending on the boat and conditions. You should be prepared to dive prior to the first diver entering the water, be ready when the divers before you are entering the water and enter as soon as you are told too.
- Initial Descent: When you enter the water, get your body into a vertical streamline position, clear your ears and locate your dive buddy. If the entry went as planned they should be close to you. Once you have located your dive buddy, position yourself into your preferred descent position, Head first or feet first, and head towards them. If they are above you, you may have to flair your body to slightly slow your descent or add a little air.
- Set your “glide path”: Once you and your dive buddy are descending try to locate your “target”. If you can not see it, continue to dropping as fast as possible. However, when you can see the “target” you may be able to adjust your descent so that you will glide to a point just up current from where you want to be. Bear in mind that you will ideally want to slow your descent so that you are not breaking suddenly to keep from crashing into the bottom.
- Follow the dive plan and enjoy your dive.
Practice Makes Perfect
Like all skills, it makes sense to learn and practice it in a controlled setting first. Dropping rapidly while in a strong current is not for everyone. It requires multitasking in an environment that does not allow many mistakes. You may need to orientate yourself, check all your equipment, adapt to the current and locate your dive buddy all within seconds. Also, it might require you to equalize your ears faster than you are able to. This could lead to ear damage, loss of hearing and maybe the end of your diving if you can not keep up. The standard procedure of ascending slightly so you can clear your ears may cause you to miss the dive site.
If you can practice this type of entry in calm waters or with just a mild current, do so. If you have to slow the descent, you are not risking being carried away by the current. It might take a few dives before you are comfortable with the entry. If it is not comfortable without a current, then do not dive with a current. You might also find that you may need to add a small amount of weight, however, most divers will not. The force of your entry should be enough to compensate for any trapped air.