Beginner’s Guide to Constant Weight Freediving (CWT)

constant weight freediving apnea cwt

Freediving is a fun activity to do recreationally, but one can also freedive competitively to reach new depths with just a single breath. One such competitive freediving discipline is constant weight freediving, and in this article we will discuss how to do it safely, the inherent risks involved, and well as the recommended equipment for it.

What is Constant Weight Freediving?

Constant weight freediving, otherwise known as constant weight apnea, is a sport where a diver must descend to depth and ascend to the surface with the assistance of only bi-fins or a monofin. The diver will swim next to a dive line the entire time, however they are not allowed to grab the line for assistance except once at the bottom to help them begin their ascent.

The “constant weight” aspect of this discipline means the diver cannot do anything to change their weight. In other words, they are not allowed to wear a weight belt, neck weight, or use a weighted sled.

They must fight against their positive buoyancy until they reach a depth where they start to freefall. On the way up, divers must contend with their negative buoyancy. As with all freediving disciplines, the diver must accomplish this all in one breath.

Comparing Constant Weight Freediving to Other Disciplines

Constant weight freediving is a specialized way of freediving that places an emphasis on performance and reaching the lowest depth in a single breath hold. Freedivers that participate in this activity are very goal-driven; their primary objective is to descend straight down as far as they can go and return to the surface safely.

This type of freediving is often performed in competitions so that competitive freedivers can determine who can set the new world record and achieve acclaim.

Other freediving disciplines are not so strict in their rules. Compare constant weight freediving to recreational freediving, for example. Recreation freediving has no rules, so divers can use whatever equipment they feel like to assist them.

Furthermore, when done recreationally, divers can enjoy their time underwater by taking in the scenery and exploring during their breath holds. Essentially, it prioritizes enjoyment over performance, which is why casual freedivers tend to prefer it over constant weight freediving. Not everyone wants to set new records and break boundaries; many simply wish to relax and enjoy their time in the water.

How to Constant Weight Freedive

Now that you have an idea of how constant weight freediving works, in this section we focus on how you can perform a constant weight freedive.

Get in a Boat

freediving by a boat

Since constant weight freediving is all about going as deep as you can underwater, you can’t exactly perform it in your neighborhood pool or in shallow reefs. You need to head out into deep water by boat so that water depth is no longer your limitation, but rather how long you can hold your breath.

Set Up a Dive Buoy and Line

It is extremely important that you have a dive buoy and line set up to guide you as you dive deeper into the water. The deeper you go, the harder it gets to orient yourself and the dive line will ensure that you continue to head in the right direction as you descend.

To further ensure they are headed in the right direction, some freedivers even attach themselves to the line using a lanyard. A secondary benefit of the dive line is that the markings on it can help you track your depth.

Put On Your Fins

Typically, constant weight freedivers will use monofins for maximum performance, however you are free to use bi-fins if that’s what you’re comfortable with. The downside of bi-fins is that it gets outperformed by monofins in terms of power. Monofins, on the other hand, generates significantly more thrust as you undulate your body.

There’s a reason why the monofin design is inspired by dolphin fins; it will help you cut through the water like one. Bi-fins can be used as a beginner to get used to constant weight freediving, however the goal is to one day upgrade to using monofins.

Bi-fins are not sustainable in the long run since they cannot replicate the strong propulsion that monofins can unless you increase your kicking rate which would only serve to drain your energy and oxygen reserves. Since performance is everything in constant weight freediving, one must make their breath last as long as possible while swimming quickly in order to maximize performance. This best way to do this is with monofins.

Dive With Buddies

As with any water activity, one should never dive alone. Shallow water blackouts or other such emergencies can occur at any time, so you should always have at least one other person on lookout just in case.

In a sport like constant weight freediving, the need is even greater since emergencies are most likely to occur on the ascent. Freedivers can misjudge how much breath they have remaining and may need to be rescued out of the water or resuscitated.


Once all of the preparations have been made, it is finally time to dive. You cannot use any weighting systems to help you, and you must descend along the dive line without touching it. The exception is when you want to turn around and start your ascent.

The entire time, stay calm and perform proper finning technique. At around 25-30m (80-100ft.) you will feel the water pressure decrease the buoyancy in your lungs, causing you to become negatively buoyant and freefall deeper and deeper. This will help you reach your desired depth, but keep in mind you must fight against this negative buoyancy on the way up, so know your limits.

Dangers of Constant Weight Freediving

Every water sport has a risk of drowning, and with an activity like freediving, the risks are even greater. As such, it should not be performed by individuals who are not confident in their swimming skills or finning technique. Furthermore, one should be comfortable with their breath hold technique and to stay as calm as possible in order to conserve oxygen.

There are precautions one can take to reduce the chances of an underwater emergency occurring. However, one cannot completely alleviate these risks, however it can be the difference between life or death.

Overestimating Your Limits

When it comes to constant weight freediving, the object is to dive as deep as possible without altering one’s weight. Oftentimes when inexperienced freedivers dive to a depth where they start to freefall, they get too caught up in the momentum and end up diving too far.

A freediver must never forget that for every bit of distance traveled during the descent, it must be traveled a second time on the ascent. Unfortunately, even if one is aware of this fact, estimating the half-way point of one’s dive can still prove to be difficult.

What we want to avoid is a situation where one reaches their “half-way” point only to realize they are nearly out of oxygen and energy. This will only serve to cause panic which will lead to mistakes, as well as increase one’s heart rate and use up their remaining oxygen even faster. With that said, how does one reach new depths and set new personal bests with these challenges in mind?

Pushing Past Your Limits

constant weight freediving with spotters
Sylvain7171 / CC BY-SA

In order to push yourself safely, you should strive to gradually dive deeper and always with at least one other experienced diver such as an instructor or a trusted spotter. Your dive progression should be well-documented and record setting attempts should be done sparingly.

By keeping a detailed log, you can objectively track your progress and make informed decisions on whether you should keep pushing ahead or take a few steps back to practice until you’re more comfortable.

When you want to increase your dive depth, make achievable goals. For instance, if you set a record of 20m (~65 ft.) on your first constant weight freediving attempt, it is reasonable to aim for a 25m (~82ft.) dive next time. But while everyone has different limits, it would not be reasonable if you tried to dive twice as far for the next attempt, so stay close to your limits.

As you try to set new personal bests, have a spotter follow you halfway down and stay there to monitor your descent. On your way back up, your dive buddy can observe if you are exhibiting any signs of distress.

If it is not immediately obvious, you can signal to your partner that something is, indeed, wrong. Whatever the case, having someone watching your back is crucial in the event that an emergency arises.

Underwater Blackouts

A blackout occurs when one loses consciousness due to lack of oxygen reaching the brain. This can occur as one pushes the limit of their breath-hold and usually happens unsuspectingly to freedivers who hyperventilate and suppress their instinct to breathe.

Since the freediver believes they still have time remaining during their breath-hold, they are blissfully unaware that their brain is not receiving sufficient oxygen and is on the verge of shutting down. Without a spotter to keep track of you, overestimating your limits would almost certainly lead to loss of consciousness and subsequently drowning.

How to Avoid Freediving Blackouts

To reduce the chances of suffering a blackout, one should take frequent breaks of sufficient length between dive attempts. Blackouts are so dangerous because they can occur even if you feel like you have sufficient oxygen in your body, which is why hyperventilating is such a dangerous technique.

That is why even if you don’t feel like you need it, you should intentionally take longer breaks to allow your body to oxygenate fully. Seriously, take a 10-minute, perhaps even a 20-minute long surface break, particularly if you’ve just performed a long dive. It’s not unheard of to rest that long in order to guarantee that the tissues in your body are oxygenated.

This is yet another reason why a spotter should be present in order to be objective when monitoring your behavior, lest you decide to do another lengthy dive without sufficient rest.

Bi-fins or Monofins for Constant Weight Freediving

Photo Credit: Emma Farell CC By 2.0

How Invested Are You?

While monofins are the best choice for constant weight freediving in terms of performance, that doesn’t mean you should go out and buy one right now. It’s necessary to consider one’s goals, both short-term and long-term. Freediving has a certain barrier to entry, in that the average person can’t just go out and freedive just like that.

First, one needs transportation (i.e. a boat or other watercraft) to head out into water that is sufficiently deep enough for your dive attempts. Furthermore, as we keep stressing above, one should NEVER dive alone; always have a spotter to monitor you. And of course, one should be proficient in their breath-hold and duck-dive technique. There are even more reasons than this in regards to why constant weight freediving isn’t a discipline that the average person can do.

Constant weight freediving requires commitment and sacrifice in order to progress as a freediver. As such, unless you know you have the desire to achieve these goals, then and only then should you consider purchasing expensive equipment to get started, or buying new equipment to replace old ones.

Going All In

Once you’ve decided that constant weight freediving is a discipline you want to pursue, it’s time to select the appropriate equipment to help you reach your goals. If you ever aspire to reach the upper echelon of competitive constant weight freediving, at some point you need to invest in a monofin.

Monofins provide the greatest return in terms of thrust generated for your energy expenditure as you undulate your body. The large surface area of the fins displaces the greatest amount of water compared to other fins which results in superior propulsion.

The water displacement is not just important on the way down to your desired depth, but also as you make your ascent to the surface. As we’ve discussed above, around the 25-30m mark is when you start to freefall. The entire time up to this point you’ve been swimming against your positive buoyancy.

On the return trip, you will be swimming against your negative buoyancy until you reach that point again. At different points during your dive you will be swimming against your buoyancy. That is why you need a monofin for sufficient water displacement to allow you to jet through the water. Without one, you run the risk of expending all of your energy and oxygen while struggling against your negative buoyancy on the way back up.

Constant Weight Freediving Recap

To recap, constant weight freediving is a competitive discipline where divers try to dive as deep as they can without changing their weight and using only bi-fins or monofins to assist them. They follow a dive line straight down and up, using it only as a guide to orient themselves, check their depth, and not for pulling themselves upwards or downwards.

In order to achieve the best results in constant weight freediving, one should learn how to use a monofin. This piece of equipment is necessary to power through the positive and negative buoyancy on your descent and ascent respectively. Without them, you may burn through your energy and oxygen reserves faster compared to using other fins, which would stifle your performance.

Furthermore, due to the inherent dangers of constant weight freediving, one should always dive with a buddy just in case. Also, between each dive, it is crucial that one rests for at least 10 to 20 minutes to fully oxygenate their body. Each dive should be logged so that you have an objective measurement of your progress. This can help you plan your dives and set new records at a steady pace.

Photo: Simukas771 / CC BY-SA