While the concept of fins is simple, the designs and options available are numerous. When evaluating which fins will best meet your needs, keep the following questions in mind:

• What do I plan on using the fins for PT/ Surface swimming, diving, Over the Beach (OTB)or river and stream crossing, will you be carrying them while patrolling?

• What water temperature range will you be using them in (so what size boot pocket will you need)

• What type of kick will you use, and in what environment, IE getting in and out of an SDV or closed in areas like around piers or caves?  

When the military first started diving, there was only basically one type of fin;(the duck fin) now there is a fin for almost every type of dive/swim. Fins are a specific piece of kit, almost to the point that you can have more than one set of fins depending on what you are going to do. Your fins are one of the only pieces of equipment that significantly affect how well you perform during your time in the water. 

Surface Fins

Typically, a more basic fin design will meet your needs. The length of the fin needed by surface swimmers is typically shorter than those needed by SCUBA divers and are they are shorter than those used by free divers. If you feel like you are fighting your fins rather than being aided by them, then your fins are probably more significant than you need. Meaning they are too big for you. Full foot fin are usually the best for this as long as the water is warm, or you can buy a set a little bigger and use a dive sock.  

Combat Swimming

Military divers tend to desire more fin features than recreational divers. They probably use a fin that has more in common with a technical / cave diver. There are two types of divers that are more aware of the propulsion power offered by their fins. SCUBA fins tend to be the same length or slightly longer than snorkeling and swimming fins, which means they require more leg strength and power to kick effectively.  

Foot Pocket Open or Closed

Water temperature will affect the gear you choose. The gear you wear can be a factor in determining the fins you take into the water with you. If you are in cold water, you will need thinker booties. The good thing about your feet is you can always go with a dive bootie in warmer water. Your feet, for the most part, will not overheat. So, you only have to worry about how cold the water is and if you have to use a thinker boot then usual. If you dive wearing boots (either neoprene or hard sole), an open-foot design fin is what you’ll want to wear. An open foot pocket accommodates boots because the heel strap was around the back of the diver’s boot and can be adjusted to offer a comfortable fit. If you wear rigid-sole boots, the open-foot pocket is the best option.  

Closed-foot fins cover your entire foot. You can still wear a dive sock to keep it from rubbing if you are going barefoot, but most people won’t need that.  

Propulsion

 Technology has help fin’s out over the last 20 years or so. If you are blindly wearing a pair of fins because it was issued and that’s all you have, you really should go to a dive shop and look at some more options. There are shoes today for running, doing CrossFit, or walking.  Fins have evolved to be the same way.

Diver fins now offer features like Paddle, Channel and Split fin designs.

Channel and Paddle

Channels help move the water across or through the fin, which allows the diver to move through the water quite rapidly. Channels increase the speed because they offer less surface area resistance in the water. The channels also offer extra flexibility, which means the fin can bend further and move more water with each kick. Modified paddle fins offer a more flexible material that is used for connecting the blade to foot pocket, cutaways in the upper portions of their blades, and soft center panels. They tend to be more flexible than traditional paddles, making them easier on the legs and ankles. The best paddles can compete head-to-head in comfort and performance with the best splits fins. It can also help on long dives with leg cramps and sore knees and angles. 

Split Fin

The theory behind split fins is as the diver kicks their foot downward when engaged in an up-tempo flutter kick, actually generate lift along with a jet-propulsion effect, similar to a boat’s propeller. The faster the propeller turns, the more propulsion is generated. With split fins, power comes from the speed of a diver’s kick rather than the force of the kick. Split fins are also popular among divers who experience knee pain or have had knee surgery. The split fin reduces the amount of resistance felt by the diver’s joints while offering a great deal of effectiveness with each kick.  

There are so many fins out there today that do some many things. It is tough to use one set of fins everything. I would also say there is no point to ask one set of fins to do anything. You can you a small set of fins for water jumps or river and stream crossing/ OBT and then when you are swimming on a long dive you can use a different pair of fins. Fins are like shoes, you have more than one pair of boots, and you can genuinely have at least two to three sets of fins that can do it all.

Lastly since is basically Independence Day weekend on July 6, 1747. John Paul Jones is born in Arbigland, Scotland. He is originally appointed to the Continental Navy in 1775, he is known for his quote,” I’ve not yet begun to fight!” during the battle between the Continental frigate, Bonhomme Richard, and HMS Serapis on Sept. 23, 1779.

In the early 1770s, a Connecticut inventor David Bushnell started designing what would be the first submersible. It was a small egg-shaped and less than eight feet tall. Her hull was constructed from two oak shells held together by steel bands and waterproof with a thick layer of tar. It had ventilation tubes, a compass, and a device for determining depth. Attached to the exterior was a primitive bomb. The pilot entered the vessel through a hatch at the top. There were a couple of small glass windows that provided very light and visibility. It was operated by a hand crank that propelled it and a tiller that steered it. The operator also controlled the hand pump that regulated the ballast that submerged and surfaced the craft. Once submerged and the ventilation tubes were closed, there was about 30 minutes worth. It was called “Turtle” because of the two “shells” put together to make it.  

In the spring of 1776, about a year into the Revolutionary War, Bushnell wrote to General George Washington asking if the Turtle could be used in defense of New York City’s harbor. Washington accepted the offer. Around midnight on 6 September, the Turtle, piloted by Army sergeant Ezra Lee. That’s right, the first submarine action by the U.S. was the Army. 

It took Lee two hours to get to his target; a British ship named the HMS Eagle. Once he positioned himself beneath the vessel, he was supposed to drill into her hull using a bit attached to Turtle’s top hatch. Once the hole was deep enough, he would anchor his explosive device to the ship’s hull. He had about 30 minutes to get away from the Eagle before the charge would detonate. That was the plan, but Lee’s bit got stuck in a metal part of the hull. On his second attempt, the Turtle bobbed to the surface and was spotted. As he headed for shore, Lee released his “torpedo,” which exploded harmlessly in the middle of the East River. Again, he was Army.  

Although the Turtle was not technically a DPV, it was the U.S. first attempt at underwater warfare. The Human torpedoes or manned torpedoes are a type of diver propulsion vehicle used as secret naval weapons in World War II. The name was commonly used to refer to the weapons that Italy, and later Britain, deployed in the Mediterranean and used to attack ships. The first human torpedo was the Italian Maiale (“Pig”). In operation, it was carried by another vessel (usually a submarine) and launched near the target. It was electrically propelled, with two crewmen. With rebreathes and riding astride. They steered the torpedo at slow speed to the target. At the target, they would use a detachable warhead like a limpet mine and then rode the torpedo away. The idea was successfully applied by the Italian navy early in World War II and then copied by the British. They discovered how effective this weapon could be after three Italian units successfully penetrated the harbor of Alexandria and damaged the two British battleships HMS Queen Elizabeth and HMS Valiant, and a tanker. The official Italian name for their craft was Slow-running torpedo, but the Italian operators nicknamed it the “Pig” because they were difficult to steer. The British versions were named “chariots.”

They were used thru out WW2, After the war, the technology started to get better, and they were used thru out the cold war to put people onto beaches and other fun stuff like that. There are many types of DPVs out there, and I think it is better for me to post a link to a site that talks about them.

en.wikipedia.org/wiki/Diver_propulsion_vehicle

There are also some other ones out there. Make sure you get proper training before trying them.

Jetboots Diver Propulsion System, (JDPS) is a unique hands-free diver propulsion system designed specifically for the military and commercial diver. JDPS uses brushless motors and lithium-ion batteries to achieve incredible propulsion at a meager total system weight, which enables previously impossible mission profiles. Jet boots were first used to help with hooking and climbing of GOPLAT and in currents. Now they are used more for getting from point A to B.

The most significant benefit of using a diver propulsion vehicle is you can go faster, cover more distance, and increase your bottom time. Since you won’t be kicking as much as you typically would be, you can stay down longer. They also help get divers into a place where because of the current you would not be able to get into. If you judge the tides wrong and trying to swim age against it, it can be impossible.  

There are DPVs powerful enough to pull multiple divers at ones. The Suex is one of the best DPV’s out right now. I have seen it pull five fully loaded combat divers. Suex makes different models that can be used by themselves or linked together to work in pairs. The Suex represent the cutting-edge technology of underwater mobility. Performance, reliability, maneuverability, are the cornerstones that make Suex one of the leaders in the underwater scooter market. Diving a Suex is an incredible experience, ensures both high level of maneuverability in overhead environments and comfort during extensive cruising.  

A lot of divers are being required to wear helmets when they are diving a DPV type devise.  SCUBAPRO makes a helmet mask system call the Odin straps. It gives you the ability to attach any SCUBAPRO masks that has quick clips directly to an Ops Core ARC Rail. They can be quickly donned and doffed. They can also be changed backed to the full mask strap. Divers should get additional training on how to pilot an underwater scooter before using them. While diving, an underwater scooter should only be used for horizontal movement. Ascend and descend using your fins. DPVs have come a long way and they are still moving forward faster and faster, in the water and in technology.

Diving in low visibility is one of the worst-case scenarios you can find yourself in whether it is in the day time or night time. Sometimes it is a lot worse in the day then at night. I say that because at night you can turn on the backlights on your gauges/ computers to help you see them. In the day, it doesn’t help as much as you would hope/ want. Many things can cause low visibility, bad weather, the type of water you are in diving in a bay, a harbor, swamp, river or third world polluted. It can also be caused by stirred something up. When you stir silt up, it is often called a silt out. This term is used more in the cave/ tech world. Silt-outs happen when you kick up the fine sediment that is found by piers or in enclosed underwater areas, like wrecks, caves, and on the bottom of open water as well, and in particular in lakes.

Silt is a type of granular material that is finer than sand and is often light, much like the type of flour. As it is very light, it is easily disturbed by movement, either from waves, current, or a diver’s body or equipment. It is carried by water currents and accumulates inside areas that are protected like in bays, harbors, and caves. In a combat environment, it is a bad thing for a couple of reasons, and it tells people on the surface that someone or something is disturbing the bottom of the water. If you are lost, it will throw you off your timeline.  

Because the visibility decreases to next to nothing, it can cause buddy separation, free ascents or descents. Inside enclosed spaces, it can be near fatal. We were doing a training exercise in a local military area.

One of the swim pairs got lost inside a Conex box that was in about 20’ of water. It took them two hours to find their way out. With no visibility, it is hard to find your way out of something like that, which can cause panic, which in turn leads to more frantic movement patterns. They did not panic, they kept following seems and found their way out, but it wasn’t easy.  

Avoiding silt-outs

The best thing to do about silt-outs is to avoid them. Buoyancy and trim control is the best way to avoid stirring up silt. Buoyancy will help you stay at a certain depth, and Trim is the ability to stay level in the water, and it will help keep your legs and fins off the bottom. Next is a proper finning technique that goes with the right fin. Try and use a good bent knee cave kick. Make sure you have a fin that can be used for a good cave and frog kick (jet fins and Go Sports) this will help  

keep you from accidentally hitting bottom. Proper training and confidence in yourself and gear will help you if you find yourself in a low visibility situation.

Should you find yourself in a low visibility situation.

1. Trust your gear and your training.

2. Maintain your depth. Notice any pressure changes in your ears from increasing or decreasing pressure and try to bring your dive computer or depth gauge close enough to your eyes to read it.

Sometimes you have to dive in a low vis situation. Like if you are part of a dive team and you are looking for something or someone. Again day time is worst then the night time because it is hard to look at your gauges. However, there is new technology that is out there that can help. A Heads-Up Dive Computer (HUD) can make it a lot easier to read you’re your gauges. A good HUD can tell you your air pressure, depth, Total time of dive, and a lot more. SCUBAPRO’s new Galileo HUD is a full dive computer with a build in GPS. Galileo Heads-Up Dive Computer (HUD). Most HUDs mount to your mask or somewhere you can see it without having to look down at your arm. They help tremendously with low visibility situations. They help you maintain your depth and also help you monitor your air pressure. SCUBAPRO’s can be mounted to different types of masks, it is was designed to be mount to a dual lens mask mainly, but it can also be mounted to the Frameless mask and full face masks, used by most search and rescue teams. I have been diving the SCUBAPRO Galileo HUD for a while now, and nothing beats it when it comes to having to dive in low visibility. It can be used for Search and Rescue, military operations, tech/cave, and recreation.

For more information contact ecrazz@clannfive.com

Self-adjusting fin straps are one of the best ways to don and doff your fins. It also makes it easier to use different size booties. Steel spring straps are a relatively new product for fins. It was invented by cave divers that didn’t want their rubber straps breaking on them in the middle of a cave. So, they took screen door springs and made fin straps out of them. Typical rubber straps have a good chance of breaking at some point. If you are lucky, it will happen as you are putting them on before a dive, not in the middle of one. While you should always try and carry a spare strap on you, replacing a strap can be a pain in the middle of a dive. 

The spring strap helps avoid most of these problems. Available for many open heel fins, spring straps permanently mount to the fin. Furthermore, spring straps typically attach using rust-resistant metal hardware. SCUBAPRO Steel Spring Straps are available for SCUBAPRO Jet fins, Twin Jet Max, Veloce fins, and the Seawing Nova fins. They are made with High-grade marine steel. These straps can replace the traditional fin strap with the added benefits of being easier to don and doff, and they will compensate at depth for the pressure underwater.  The flexible nature of the spring strap tightens as you descend to compensate for the crush on your boots, meaning your fins stay on at the exact tension you set them to at the surface.

Spring straps are strong springs with a rubber or nylon heel cover for comfort. Instead of having to adjust the tension every time you put them on like with traditional straps, you simply stretch the spring over your heel.  

This decreases your time and energy spent putting on and taking off your fins before and after a dive. Several models of fins now come with spring straps pre-installed, but they can also be added to many fin models.

The other type of self-adjusting straps is made from quality marine-grade bungee designed for years of reliable use. Marine grade bungee is design and construction, making it ideal for prolonged exposure to moisture, sunlight/UV radiation, and the general wear and tear that fins regularly go through. A denier Dacron polyester cover is thick and long-lasting, repelling water and resisting abrasion better than nylon. Made from a top-quality first extruded latex rubber, this bungee has a consistent 100% stretch and high modulus that won’t lose its elasticity as many others do. Bungee straps are depth compensating as they compress when your neoprene boots get thinner due to increased water pressure. Like the steel spring, the bungee is self-adjusting at depth. Upon ascent, they decompress keeping fin straps comfortable throughout the dive. Straps have a large rubber finger loop to aid in donning and doffing. Marine bungee is highly reliable and has a very low percentage of breaking. All this being said, I know you can break it if you “test it” to try and prove me wrong.