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Being Horizontal… ‘Cave Trim’ – the elusive goal

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Watch a group of well-trained divers in the water — especially cave divers or technical divers — and you’ll notice they look a little different to most casual sport divers.

How different?

Well, the cave/technical/well-trained sport divers will be lying on the water (usually horizontal) rather than standing in it. Here’s what I mean:

A typical cave diver in trim… lying on the water
Photo: Tom St George

And here’s a picture of a group with a different in-water attitude:

A diver enjoying the water but working hard…
Photo: Dean McConnachie

So, let’s assume you’re not looking at those pictures and saying to yourself: “What’s the big deal?” Or “I can’t see any difference.”

Given that, let’s also assume you are interested in finding out why cave trim is preferred over the other. It’s not that anything other than horizontal is wrong. It’s just there’s something easier and better. (For the record, horizontal trim is not always exactly horizontal — occasionally the correct attitude in the water is head or feet down at varying angles for short periods — but it is the default.

Reason one to be horizontal: moving through the water is easier. You are streamlined and therefore water resistance moving ahead and backwards is at a minimum. Even with extra gear (more bottles, pockets full of tools and spanners, a pouch with backup mask, spare dive computer, lights, bits of string and a chicken sandwich), moving through the water in any direction is easier compared to swimming at it full-frontal. When a diver is streamlined, the thrust from each and every fin kick is translated into graceful movement. Progress from point A to point B and back again is more efficient, less work, uses less energy, uses less gas.

Reason two: when a diver’s flat in the water, she meets maximum water resistance going up or down. This helps her maintain position in the water column. Of course, this is a small effect compared to having buoyancy dialled in, but it’s nevertheless a factor.

One salient point when comparing cave trim to fins down orientation, is that being horizontal teaches good habits regarding buoyancy control. There is no temptation to kick to stay in place as there is with fins-down orientation. (For example, although the group picture above isn’t a video, I’d lay dollars to donuts that the two divers on the left and the one on the right are all working hard to maintain their position in the water column while the picture is being taken. They seem to have poor buoyancy control, and staying in place is an effort for them.

The cave diver pictured above is motionless, and literally hanging in the water waiting for the photographer — Tom St. George — to signal “okay. Got it!”)

Reason three: a diver in horizontal trim is much less likely to stir up silt and mud or damage whatever is below them. In fact, when using the correct propulsion technique (frog kick generally) and by keeping the knees bent and thighs parallel to her lateral line, a diver can be a hand’s breadth from the bottom and move without disturbing anything at all. This diagram may help illustrate the point.

When in horizontal trim, arch the back slightly by clenching your butt cheeks… think “Flamenco Dancer Skydiving.”
Illustration courtesy of Andy Davis, Scuba Tech Philippines

Okay, so how does one attain horizontal trim?

In a word: practice.

In more detail: commitment and practice!

Practice needs little explanation. Be patient, spend the time. A great approach is to dedicate a few dives to nothing but working on trim.

For an in-water exercise, get to a pool or shallow, calm waters, and dive with a buddy who has an underwater video camera to track your progress. Start by resting prone on a flat ledge or the pool bottom and gradually add a little lift to your buoyancy cell.

Critical to mastery is sticking to it (that’s the commitment), that and understanding the relationship between four things: gravity, buoyancy, you, your gear.

Essentially, you need to balance each of these things to come up with a perfect result. Luckily, two of them are constants and pull in exactly opposite directions. Gravity pulls you deeper, buoyancy pulls you towards the surface.

Simple… well, almost. What complicates matters are the other two things: you and the gear you are wearing.

Now let’s just say for brevity, you have reached the point where you have gravity and buoyancy perfectly balanced. Something called neutral buoyancy. You are not overweighted. You are not under-weighted. And in shallow water you are able to hover without moving your hands and feet.

At this point — hovering — you’re off to a great start. But now you need to get horizontal and stay there without moving your hands or feet (don’t scull, don’t swim, just hang in the water). Try it. If you’re lucky, it will work. Most likely though you’ll either tilt head down or feet down.

Let’s think about that situation for a minute.

As a for instance, say you need two kilos of ballast (lead weight) to achieve neutrality. These weights are over and above the ballast that’s a result of your scuba cylinders, lights, reels, and all the other crap we carry with us on a dive.

Now, divers usually carry lead ballast around their waist, so let’s says yours is about your mid-point. Now consider what would happen if we were to move that weight to the ends of your fins. Your feet would naturally swing down pulling you, your body, your kit, into a straight up and down orientation. Kind of similar to what happens when a “robust” child get on one end of a teeter-totter (a see-saw) and the “runt of the litter” is sitting on the opposite end.

Okay, so what would happen if you were silly enough to put the weights on your mask strap. Well, to begin with you’d orient head down and then your mask would most likely fall off. Goodbye mask. But if we think about the see-saw situation, same deal except now runt’s pet elephant is sitting on his lap and Robusto is up in the air.

You get the point. You are dealing with a lever. To achieve balance, either the weights on both ends have to be similar, or the distance from the balance point — the fulcrum — has to compensate for any difference. That’s to say, moving stuff that sinks in the water — weights in this instance, but also all the other bits and pieces of kit — is going to have a direct effect on in-water orientation.

Weights sink, so do scuba cylinders, lights, cameras, and a whole lot more including the gas we breathe (more than 2.5 kilos of “air” in a standard aluminium 11-litre tank for example). Understanding that moving each of these things away from your balance point has the potential to influence trim is key.

To achieve cave trim you want balance. Moving things around — even swapping light fins for heavier ones — can make that happen… or not.

But before that, you perhaps should consider things that have an effect on buoyancy: lungs, buoyancy cell (BCD, wing, etc.), drysuit, thick wetsuit. And each of these is a variable.

Also — and this is where things get interesting — things that are buoyant supply lift and the location of that lift can have an influence on trim as well. (Ask a new drysuit diver about their experience with floaty feet.)

You can experience something similar by moving a cylinder up and down in its retaining straps on a standard BCD.

All this serves to show us that the see-saw analogy used earlier may actually be an over simplification. It would be better to think of a fully kitted diver as a beam with a variable balance point rather than a simple lever with a fixed fulcrum.

Hang on. This has started to get a little over-the-top and way too complicated to explain without using Venn diagrams and video. No worries. Let’s stop now while we’re ahead because in truth, the take-away is essentially unchanged. You have the basics. Now let’s get in the water and practice.


Steve Lewis’s new book, Death in Number Two Shaft: the underwater exploration of Newfoundland’s Bell Island Mine, is available now on Steve’s website or from Amazon UK

Find out more about Steve at www.techdivertraining.org.

Steve Lewis is an author, adventure travel writer, and generalist, who dislikes dive gear but who loves to dive. A specific interest is cave diving, which he regards as "the most creative way to learn mindfulness, meditation, and relaxation.” He lives in a converted schoolhouse in Ontario’s cottage country with coyotes, white pines, and the Great Lakes as neighbours.

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PADI meets with Maldivian Ministry to confirm protection of sharks

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Over recent weeks, there has been speculation about the possibility of the Maldivian government lifting the ban on shark fishing in the country’s waters. PADI®, and the dive industry at large, were instrumental in establishing these protections over a decade ago.

With concern for the continued protection of sharks in the Maldives, the PADI organisation and Project AWARE®, along with 200 concerned local and international stakeholders opposing the lifting of the shark fishing ban, called on the government to continue to enforce the legal protections of sharks. PADI staff met with Maldivian Ministry of Fisheries, Marine Resources, and Agriculture Zaha Waheed to reinforce the position of the dive community and critical role sharks play in dive tourism.

In those meetings, Minister Waheed assured PADI that the Ministry of Fisheries, Marine Resources, and Agriculture has no intentions to lift the ban on shark fishing. She affirmed that they remain committed to sustainable and responsible management of fisheries and marine resources in the Maldives. On 20 April 2021, the Ministry of Fisheries, Marine Resources, and Agriculture released a statement asserting that “the Maldives does not intend to permit a targeted shark fishery in the Maldives.”

“Sharks are a dominant force in dive tourism in the Maldives. We congratulate the Maldives’s commitment to their ongoing protection,” says Drew Richardson, President and CEO of PADI Worldwide. “The Maldives continues to lead by example, among the most progressive countries on this critical issue.”

There are currently 17 shark sanctuaries in the world; the first established in Palau in 2009 and others in popular dive destinations including French Polynesia, Honduras, The Bahamas and several others in the Caribbean. The Maldives shark sanctuary was established in 2010 and covers 916,000 km2 (353,000 square miles).

Tourism accounts for an estimated 25 percent of Maldives’ GDP (according to 2014 figures), with diving and snorkeling being the most popular tourism activity. Prior to the formation of the Maldivian sanctuary, shark fishing was worth US$0.7 million to the Maldives’ economy, compared to US$2.3 million from shark tourism. In 2018, the shark sanctuary increased dive-trip demand in the Maldives by 15 percent, raising an additional US$6 million. Consumer research indicates that any re-opening of a Maldives shark fishery could potentially decrease dive tourism demand by over 50 percent, which could result in a loss of US$24 million.

Sharks are some of the most endangered species in the ocean, with recent research showing that the global number of oceanic sharks has declined by 71 percent. Over a third of shark and ray species are threatened, facing an increased threat of extinction, primarily due to overfishing.  There are an estimated 600,000 shark watchers globally spending $314 million per year and directly supporting 10,000 jobs. Research indicates these figures are expected to rise as global tourism returns to pre-pandemic levels.

As part of its commitment to ocean conservation, PADI will continue to stand up for sharks and advocate for their protection. For more information on responsible shark tourism, read Project AWARE’s Guide to Best Practices. To learn more about PADI’s efforts and how you can join the community of PADI Torchbearers working to save the ocean, visit padi.com/conservation.

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Miscellaneous Blogs

The BiG Scuba Podcast… with Rosemary Lunn

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Ian and Gemma chat among themselves and are also are joined by well-known Dive Industry Professional Rosemary Lunn.

We talk about dive fitness and entering the CrossFit 2021 open games and being members of our local CrossFit Box. You can also listen to our new member of the team – Rosemary Lunn – answer some scuba diving questions.

Find out more about Rosemary at www.tumc.co.uk.


Find more podcast episodes and information at the new www.thebigscuba.com  website and on most social platforms @thebigscuba 

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Explore the amazing triangle of Red Sea Reefs - The Brothers, Daedalus and Elphinstone on board the brand new liveaboard Big Blue.  With an option to add on a week at Roots Red Sea before or after. 

Strong currents and deep blue water are the catalysts that bring the pelagic species flocking to these reefs. The reefs themselves provide exquisite homes for a multitude of marine life.  The wafting soft corals are adorned with thousands of colourful fish. The gorgonian fans and hard corals provide magnificent back drops, all being patrolled by the reef’s predatory species.

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This trip will be hosted by The Scuba Place.  Come Dive with Us!

Call 020 3515 9955 or email john@thescubaplace.co.uk

www.thescubaplace.co.uk

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