Archive for the ‘Basic SCUBA’ Category

How Long can a Scuba Diver Stay Underwater?

Sunday, January 30th, 2011

I provided a simple answer to this question in a post last winter.  Over the past year, this post received a large number of hits, so it’s obviously this is a question that is often asked.   Therefore, I wanted to expound on the previous post.

There is no short answer to this question.  Ultimately, the limiting factor is either available gas, or environment.   The environmental factor here is cold.  Water transfers heat 25 times faster than air.  Even 80 degree water robs your body of heat.  This is why exposure protection is needed.  For the rest of this discussion, let’s assume there is sufficient exposure protection for the given water temperature.

Now the time limit is just a function of the available gas.  Let’s breakdown the answer based on type of diver.

Free Diving: Here the divers plunge to some amazing depths on one breath of air, and stay for several minutes before returning to the surface. Inflatable Water Slide The limiting factor is the individuals tolerance for low Oxygen, and high CO2. I believe the current record is 124 M unassisted.  The maximum duration for static (resting) breath hold is 11 minutes 35 seconds.

Basic Scuba Diving: Here there are two limits:  The available gas in the diver’s tanks, and the no decompression limit for the depth.   There is a detailed explanation of the factors involved, but an average diver can stay between 60-80 ft for about an hour.

Technical Diving: Divers are limited by the number of tanks they use during the dive.  Some exceptional dives have been for over 18 hours.  Clearly a great deal of planning is required for these types of dives.  More routinely Technical Divers often go to 150-250 ft with durations around 90-120 minutes.

Rebreather Diving: A rebreather (as described here) removes the gas limitation, but imposes a limit on the duration of the scrubber material.  Based on the construction of the rebreather, this is usually between 3 and 11 hours.  The limiting factor here is the number of tanks a diver is willing to bring in case of rebreather failure.

Commercial Diving: These divers are provided gas from a surface vessel or station.  This technique also referred to as surface supplied, does not have a limit on the gas available.

Saturation Diving: In this case the divers body is completely saturated with inert gas.  In some cases the divers will utilize a habitat between dives.  This provides an area where the diver can warm up, and take food and liquids.  In essence there is no limit to the duration that a diver can live in saturation.  The down side is the extremely long time needed to decompress.

I hope this helps answer the question.   If you have any questions on this subject, send me a comment below.

Notes on Diver Etiquette

Monday, November 15th, 2010

The other day, I found myself in a discussion with a group of instructors and experienced divers over the issue of diver etiquette.  Everyone agreed that this varies wildly from diver to diver, and shop to shop.  While there is no explicit place for this discussion in the training curriculum, it is a subject that should be brought up.   We all agreed the best time to teach this is as part of the Open Water class (teach good habits before divers learn bad ones).  Many of us do include a few minutes to discuss this in class, then try to reinforce the concept during the open water dives.

Unfortunately, there are other instructors that do not understand the need, do not have the time, or just have bad etiquette themselves.

Ultimately, a diver’s etiquette will reflect their own personality.   A diver that only thinks of them self, will never follow good etiquette.   Someone that is considerate of others will try their best to be considerate while diving.  However, many of the latter do not know how to do this as new divers.  Here are some points to consider.

  1. On the surface:
    In many dive locations, gear space is limited.  This is especially true on dive boats.  Being conscience of this and trying to minimize the space we use is good etiquette.  Here are some points to consider on a dive boat.  These points also apply to other dive sites, but boats are usually the most space limited.

    • Gear boxes and bags. Try to keep gear containers no larger than necessary.   Try to bring containers that fit neatly under benches.  Divers showing up to a boat with over sized bags or too many bags are being inconsiderate of others, and will often get glares or rebuke from the crew. I recommend three containers:
      1. One for the BC and dry / wet suit
      2. A small one for dry gear.  A backpack works for me  (phone, towel, snacks, a few spare parts …),
      3. A small crate (about the size of a milk crate) for misc Scuba gear (reel, lift bags, lights… with fins on top)
    • This configuration works well in most environments of the North East.  On a boat, the crate  should fit well under the bench where you are setting up your tanks.  The drysuit goes in a dry location until needed.  The backpack is always in a dry location.
    • Put gear away promptly. Once your gear is loaded, set up your tank and stow your gear neatly out of the way.  The same is true after a dive.   As you take your gear off put it back into your crate and stow it neatly out of the way.  Not only is this good etiquette, but it can prevent gear damage or loss on a busy deck.
    • Dive Planning: Keep in mind that your not the only one on the boat. I recall several occasions where the entire boat was waiting over half and hour for one customer to finish his dive. If you plan on doing longer dives, then try to get into the water quickly.
    • Clean up after yourself: It’s amazing to see how much debris is left after the divers remove their gear from a dive boat. Half empty water bottles, cans, partially eaten bags of food … Yes, the crew will clean the boat, but all of this is in everyone’s way during the trip too.
  2. Gearing Up This is a process that takes up both space, and time. Here are some items to consider when working to don our gear in limited space.
    • Timing: If you know that you take longer than others to gear up, then either start gearing up early, or wait for others to go first.
    • Lend a hand: If you decide to wait for the diver next to you, then give them a hand.  That way they are out of your way quicker.
    • Be self sufficient:  This takes some time to learn, and practice. Most boat crews are eager to help in any way they can. However, there are often a lot of divers gearing up at once. Before strapping on tanks, prep the gear so that it is in reach as you don your kit. Watch an experienced crewmen.  Most can gear up with no assistance.   Again, it’s not that assistance is unavailable, but if you need lots of help, then you’re preventing other divers from getting any.
  3. Underwater: This can be difficult, since it’s not easy to know where other divers are in relation to yourself.  However, here are a few items to keep in mind.
    • Look around you. There may be other divers near you that you’re not expecting.   This is especially true on or near the up-line.  Be careful of your finning when you know other divers are near.  Fin slowly until you know your not going to kick a fellow divers.
    • Steer clear of classes. If you see an instructor working with a class, try to keep a reasonable distance.  Otherwise, you may confuse and distract the students from following their instruction.   Also, additional divers in close proximity makes it difficult for the instructor trying to keep watch over his students.
    • Photo ops: This is more of an issue in warm water diving, but keep in mind that other divers may want to take a picture also.  I’ve had video footage ruined by a diver sticking his fin in view while recording.  On the other hand, I try not to take too long, and let the next photographer get a chance.
    • Reels: Keep your line reel low and secure.  On several dives, the wreck looked like spider web with lines draped here and there.  Near the up-line it’s important to tie your reel low and put wraps close to the wreck.  A line 10 ft off the wreck can become an entanglement hazard as it is out of an approaching divers view.  When passing across another line, pass your line underneath.   Assuming your on your way out, the other diver should be on his way back before you, and will not be delayed by your line.


Again, many of these points apply anywhere, not just to dive boats.  Any time space is limited, we need to work to make maximum use of it.

These were some of the points our group discussed.  Let me know if you have others.

SCUBA for the warm water diver

Wednesday, February 18th, 2009

Many divers live in tropical climates, or only dive when they travel to these climates. Up north they are often called Caribbean divers, or blue water divers. I prefer warm water divers, as many travel beyond the Caribbean, and blue water is often used in reference to very deep water.

Diving under these conditions can be both exciting, and relaxing! The scenes of tropical reefs and colorful fish are beautiful and serene. The diving is often easy and at many resorts it’s supervised. This is a great place for beginning divers to practice their new skills, and enjoy the wonders of underwater world.

We previously talked about basic SCUBA gear, so now let’s add a few items for tropical diving.

Exposure protection:
This will be the major consideration. There are a few variables here:
Water temperature
Air temperature
Your bodies reaction to cold
How many dives are planned

Read the section on Exposure Protection for more details

Tropical diving is often done around small islands. Sometimes in strong current. Separation for the boat is a real possibility, and signal devices can be real life savers! If your planning a drift dive, then will need a marker to let the boat know where you are. Inflatable Water Slide A visual aid like an SMB is ideal for both situations. Also a audible signal like a whistle, or Dive Alert can get the attention of the dive boat when you’re hard to see. Both of these can be easily carried in a BCD pocket.


Buddy Skills: With all the fascinating beauty of the tropical reefs, it’s all too easy to become distracted and lose contact with your buddy. Try to stay within about 10 ft, and don’t forget to check on them regularly.

Depth Control: The clear water can be very deceiving. Remember objects appear closer under water. We can easily go deeper than planned, and run into issues with gas management, or decompression. Keep an eye on your gauges!

Buoyancy Control: Coral reefs are fragile environments! A single kick can kill an organism that has lived for 100 years. We as divers are fascinated by this spectacle, but we must protect it from ourselves. Work on your buoyancy. Practice it whenever you have a chance.

SCUBA Exposure Protection

Wednesday, February 18th, 2009

In the process of diving, we are subjecting our bodies to an alien environment. This environment exposes our bodies to conditions that we are not accustom. Divers need protection in a few different forms:

  • Thermal protection: The major reason for protection is Thermal protection. Keep in mind that water conducts heat 25 times faster than air. In air, our bodies would be warm at 75 deg F. Underwater, most people would chill very quickly at 75 deg F. Our bodies can not tolerate a drop in temperature. Hypothermia develops after a drop of only a few degrees.
  • Abrasion protection: Rocks, shipwrecks, shells, corals can all easily scratch, or cut through exposed skin.
  • Marine organism protection: especially in tropical waters, there are many stinging organisms both on the reef, and floating in the water. Sea Urchins, scorpion fish, lion fish and a long list of others have sharp if not poisonous barbs that can easily hurt a diver.
  • Sun protection: While not as obvious, the sun in the tropics can burn sensitive skin on the deck of a boat, or even while we are snorkeling in the water.

The type of protection available breaks down into three groups:

  • Dive Skin: These provide no thermal protection, but do provide the other three. They are often made of Lycra to hold the suit close to the body and reduce drag.
  • Wetsuits: These are made of Neoprene rubber, which consists of thousands of small gas bubbles. The thicker the wetsuit, the more bubbles, and therefore the more thermal protection it provides. The thickness is measured in millimeters (mil) and varies form 0.5 – 7.0. A small amount of water enters the suit (hence the name) but the body quickly bouncy castle for sale warms this water, and the suit insulates it from the outside water. In order to work properly, they must be snug to prevent water from flushing through the suit and cooling the body.
  • Drysuits: These provide an airspace under the suit that can be inflated to provide protection. An undergarment holds the air in place around the body and reduces air movement to the highest part of the suit.

Which to use:

Since each diver responds differently to cold, it’s impossible to give an exact answer. Here are some factors that affect how much thermal protection is needed:

  • Water temp: Duh. Colder water will need more protection.
  • Depth: Often it is cooler down deep, and wetsuits will lose some of their protection as we go deeper.
  • Air temp: On an overcast day, it can be cooler in the air than under water.
  • The diver: Size, fitness, metabolism, even what was eaten for breakfast will all affect the reaction to cold.
  • Length of dive: Longer exposures will require more protection.
  • Number of dives: More dives done in a day or over a week can cool our bodies slowly.

There is no right suit for all divers under a given conditions. No one can say “you’ll be warm in a 3 mil suit at 80 deg F.”. However, here are some guidelines:

Dive skins are used in very warm water ( over 85 Deg F ). They have little to no thermal protection, but do provide a layer of protection from sun, scrapes, and stinging organisms. In tropical environments, this protection can be very important. Corals, sea urchins, and shells can cause punctures and abrasions. Also, the Caribbean sun can cause dangerous sunburn very quickly. If you don’t need the thermal protection, it’s still advisable to wear some form of dive skin.

If the water temperature is below 85 degrees, many people should consider a 3 mil wetsuit. At 80 degrees, many will wear a suit between 3-5 mil. On the other hand, some very cold people will where a 7mil suit. As the water get colder, the thickness of the suit can be increased.

Since water temperature varies throughout the year, it can be beneficial to consider layers. A 3 mil shorty can be worn over a 3 mil suit when the weather turns cold. Or, a hooded vest can be warn under a suit to keep the core warm.

Below about 60 Deg F, many people are thinking drysuit. Some will stay with a wetsuit as long as possible due to the cost of a drysuit. For longer dives in colder water, drysuits are heaven sent. With a drysuit, dives under the ice in lakes are possible. To handle cooler temperatures in a drysuit, the undergarment thickness is increased to create a larger air space around the diver. Some exotic materials are often used in the undergarment provide more thermal protection for the same size air space.

Unfortunately, when discussing thermal protection, there is no right answer. It all depends on the diver, and trial and error may be the best approach. One parting point: If you’re warm, you can flush water through the suit, or remove your hood to cool off. If you’re cold, you have to end the dive to warm up. It’s better to error toward the warm side.

Points to consider when buying dive gear

Sunday, January 25th, 2009

Any basic SCUBA class will tell you that the primary consideration when buying gear is fit. If it does not fit right, it will not function properly. The best example is the simple SCUBA mask. If it does not fit, it will leak, and fill with water. This not only defeats the purpose, but also adds a great deal of stress to the diver. Make sure your gear fits!

After fit, here are some other considerations you may want to keep in mind when making gear selection.

Intended use: Ask yourself a serious question: what type of diving will you be doing in 5 years? Your SCUBA gear will easily last that long. I still regularly dive the first SCUBA regulator I ever bought. Many fall victim of short sighted purchases. Then every few years, they sell all their gear, and buy gear that is better suited to the diving they are doing now.

Marketing claims: The newest or most expensive model is not always the best choice. Manufacturers are constantly trying to separate themselves from the others. Inflatable Water Slide There have not been huge changes in SCUBA technology in the last few years. Improvements in manufacturing practices have reduced the cost to make the gear, and exotic materials have made some of the gear more rugged. However, despite marketing claims, the basic function of the gear has not changed significantly.

Local Conditions: Ask a few local divers, or instructors, what type of gear they use and why. There are a few pitfalls to this approach. If their answer is one of the following, “it was a deal”, “someone else recommended it” or “That’s what our shop sells”, then look for another source. Keep in mind that shops recommend what they sell. That does not mean its the right gear for your local diving. Check out the diving experience of the shop owner (the one who purchases the gear). Make sure their diving matches your plans. If not, then the gear may not be suited to your diving conditions.

A good instructor will usually be upfront, but some are affiliated with a shop, and will promote the shop’s gear. Experienced divers will get the right gear for the job. Find out what it is and why.

Shop for features not brands: When talking with other divers, ask about the features they look for in the gear. During these discussions, leave the brand out of it. Most brands offer similar features. Or put another way, the features you’re looking for are probably available from several brands. The important part is to determine which features are important, and which are not. Some features, highly touted by the marketing types, may be a detriment in your diving conditions. Make a list of the features you want before stepping into the shop.

Which brand: Again, most features are available from several brands. How do we choose? Without going into the Chevy vs Ford issue, here are a few points to ponder:

  • Service: Some brands provide fantastic gear, but have very few locations for service.
  • Quality: Some brands have better manufacturing processes, and produce gear with better fit and finish.
  • Reliability: This often has to do with the quality of the materials used in the gear, and the quality of the engineering that went into it. Simple is usually more reliable.

Price: Why is this last on my list? Simple, if you have not chosen good gear, then getting a good deal, is no deal at all. I hope the above discussions will prevent you from purchasing the wrong gear, or falling for the marketing claims and purchasing unnecessary bells and whistles. If you can avoid those pitfalls, then you should have saved enough money to buy the right gear once.