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Being Horizontal… ‘Cave Trim’ – the elusive goal
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.
Residents in the North East awoke to a stranded sperm whale on Majuba beach in Redcar on Sunday morning. Little did they know, however, this was not in fact a real whale, but an art installation created by Captain Boomer Collective in cooperation with Zephyr Wildlife Productions to raise awareness about the plight of our oceans.
The realistic, life-sized sperm whale attracted crowds of people as ‘scientists’ imitated taking samples and measurements to establish the cause of stranding. A handful of BDMLR Marine Mammal Medics also attended the scene to assist with the ‘incident’ and educate the public. The Teesside region has seen high rates of mortality among several species recently, crabs and harbour porpoises to name a few, so this publicity stunt couldn’t have come at a more relevant time.
The whale, which is still situated on Majuba beach, will remain there until 4pm today before it will then be moved on. If you’re in the area, we’d highly recommend going to check it out!
REMEMBER, if you ever see a stranded whale (or dolphin or porpoise):
🐳 Call the BDMLR hotline to report it and for advice on what to do next ☎️01825 765546 (option 1)
🐳 Keep a safe distance, keep noise to a minimum and keep all dogs on leads
🐳 Do NOT touch or attempt to move the animal – cetaceans often carry zoonotic diseases/viruses which are transmissible to humans. There is often an underlying reason for them stranding too, so even if you were able to refloat them in the water, there’s a strong chance the animal will restrand.
For more information about the Captain Boomer Collective visit their website by clicking here.
For more information about British Divers Marine Life Rescue click here.
Photos: Sally Bunce
Oceania has a fascinating mixture of well-known romantic destinations and wild, remote dive spots that few people ever get to visit. It is a region of contrasts with enough dive destinations and cultural highlights to satisfy even the most adventurous divers. In part II of 12 great places to go diving in Oceania, we take a deep dive into some of this region’s most famous and little-known islands. Get inspired for your next dive trip to Oceania here.
French Polynesia
French Polynesia’s Society Islands have a stellar list of dive destinations, including Tahiti and Moorea. Between them, they offer easy coral reef diving and calm, turquoise lagoons with friendly stingrays and blacktip reef sharks. You can also swim with humpback whales, tiger sharks, lemon and nurse sharks there.
This beautiful nation’s best-known dive spots, Fakarava and Rangiroa atolls, are just a short flight away from the Society Islands. Both of these huge atolls offer exciting pass dives with hundreds of grey reef sharks and resident dolphins.
For a completely different dive experience, visit the Marquesas Islands. This island group is the farthest from any landfall on Earth and has a unique underwater world that hosts unusually large mantas and melon-headed whales.
And if that all sounds like too much effort, go Bora Bora scuba diving instead. This ‘Pearl of the Pacific’ has fantastic diving, and you can spend your downtime relaxing with champagne lunches on deserted islands.
The Solomon Islands
The Solomon Islands are a haven for more than 1000 reef fish species and numerous prized critters, plus dolphins, sharks, rays and six species of sea turtle. Hosting hundreds of wrecks and remote hard coral reefs, there is something for every diver there.
The Russell Islands host some of the best-known dive sites in all of the Solomon Islands. There, you can glide between the walls of a crevasse that cuts through an island, immerse yourself in wreck diving at White Sand Beach, swim through a halocline at Custom Caves, or go in search of pygmy seahorses.
For the best wreck diving, make sure you visit Iron Bottom Sound. This stretch of water hosts around 200 ships and more than 600 aircraft wrecks from World War II. It is a wreck diving mecca that offers excellent tech-wreck dives.
The Marshall Islands
The Marshall Islands is a chain of volcanic islands and coral atolls that few people know about. As the fifth least visited country in the world, these islands offer remote diving among exciting deep wrecks and vibrant coral reefs.
Bikini Atoll is the main dive destination in the Marshall Islands. Made famous by US atomic bomb tests in the 1940s, this atoll hosts numerous deep wrecks that offer incredible tech diving.
As well as some of the best tech-wreck dives imaginable, the Marshall Islands also have thriving hard coral reefs without any dive crowds. There are pinnacles, drop-offs, channels and shallow coral gardens to explore, busy with colorful reef life.
The Cook Islands
When it comes to warm welcomes, it’s hard to beat the Cook Islands. From the moment you arrive, you will be drawn into one of the friendliest nations in the world and won’t want to leave.
This wonderful country is a perfect place to get your Open Water Diver certification or take your family diving. Rarotonga is the main destination for tourism and is a charming island with fresh markets, cafes, restaurants, and resorts tucked away among the palms. There are around 25 dive sites just offshore and gorgeous beaches for laid-back surface intervals.
Nearby Aitutaki has fewer visitors, yet it hosts around 22 dive sites, with many still being discovered. It is a great place to dive among remote coral-covered landscapes and forget the rest of the world exists. Whichever island you choose, the waters are warm and full of colorful reef life.
New Caledonia
New Caledonia is one of those wish-list destinations known for its spectacular diving, crystal-clear waters and abundant marine life. Unlike some remote destinations in Oceania, New Caledonia has modern infrastructure that makes it easy to explore at your pace – by car or island hopping with regular domestic flights.
There are over 100 dive sites scatted around New Caledonia, offering a tempting mix of deep drop-offs, thrilling drift dives, wrecks, and easy reef diving. Most diving is conducted at the New Caledonia Barrier Reef, a vast 1500 km-long reef that encloses a UNESCO World Heritage lagoon. Within the lagoon, you can explore coral-encrusted walls, channels, and easy dive sites in shallow waters.
New Caledonia’s extensive marine reserves ensure these dive sites are teeming with life. For the best chance to see mantas and sharks, visit from April until September.
Vanuatu
Vanuatu is the perfect place to reconnect with nature, offering untouched rainforests, natural swimming holes and excellent scuba diving.
Pristine reefs abound in Vanuatu, with many dive sites accessible simply by walking off the beach. Million Dollar Point is one of the most unique dive spots and hosts an array of machinery and equipment dumped by the US after World War II. The SS President Coolidge, a former World War II troop carrier, and the 1874 three-masted Star of Russia are excellent wrecks to dive.
The amount of marine life at Vanuatu’s dive sites is staggering. As well as rainbow-hued corals and countless reef fish, there are sea turtles, sharks, rays, and numerous pelagic fish. You can also go swimming with dugongs there.
Papua New Guinea
Papua New Guinea is one of the most culturally diverse countries in the world, home to more than 850 known languages and hundreds of different tribes. It is unlike anywhere else in Oceania.
Along with the Solomon Islands, Papua New Guinea has some of the healthiest coral reefs in the world, including at Kimbe Bay. This special bay was once ranked as the most beautiful reef by National Geographic.
The nearby Witu Islands are a great place to go critter hunting and drift dive among schools of tuna and barracuda. Milne Bay is the home of muck diving and offers excellent shallow muck and reef diving with numerous critters.
There are seamounts busy with reef sharks and exciting walls at Fathers Reefs, and you can dive in the shadow of jungle-covered fjords at Tufi.
Kathryn Curzon, a shark conservationist and dive travel writer for SSI (Scuba Schools International), wrote this article.
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