I am always up for the deep, cold, long challenging dives.

So when an opportunity came along to dive the wreck of the Pinthis, I jumped on it. The wreck is nearly 100 feet of deep freezing waters (barely hitting high 40s), a rough (flat seas) and long (40 minutes) trip from the (rich and prosperous) town of Scituate MA.

In any case, my buddy Sam and I drove down that morning of the fifteen of August, 2008, from Boston to Scituate. Sam was diving his Meg rebreather and I dove my O2ptima. We boarded Fran Marcoux’s excellent boat, the DayBreaker, in the Scituate marina.

Except for the fact that my VR3 shut down at 30 feet, the dive was pretty great, the weather gorgeous. The Pinthis is a great turtled oil tanker, which you can penetrate through and through. Plenty of cods inside, a few lobsters and large crabs as well as sunflower seastars. I also saw a very large flounder, not that Sam would care for he only loves rusting metal.

The followin is my first attempt at taking a video of a boat dive and using my video lights so please be nice:

Wreck of the Pinthis from Erik Dasque on Vimeo.

Note that the first song is an original sountrack that was written for my father’s underwater documentaries serie called “Le Monde sous le Masque”

If you’re a rebreather diver in new england, make sure to let us know and we’ll dive together !

Dive data:
Wreck of the Pinthis, 08/15/08, AM, Fran Marcoux Daybreaker, departing from Scituate

• dive 1: 99 ft – 43 mins – 46.5 degrees
• dive 2: 100 ft ! – 39 mins – 46.5 degrees

I am copying here two comments made on the original post:

John Stull says on Tuesday, September 2nd, 2008:
Pretty eerie…my mother-in-law’s father was the captain of the Pinthis – died in this wreck when she was only 9 or 10. The first section was a bit long but I really like the music and the vivid colors…it would have been nice to have some narration of where you were in the wreck…but it surely would have ruined the mood.

Carol Phelan said on Tuesday, September 28th, 2010
My grandfather, John Phelan, was the oiler and perished in this wreck. Chilling to see the silent beauty of the dive. Thank you.

But if you’re looking for a used rebreather, RebreatherWorld is the place to go. It’s a very tight community where you’re unlikely to get scammed. There you’ll find AP Diving Inspiration and Evolution rebreathers for sale as well as ISC Megalodon Rebreathers, Dive Rite O2ptima rebreathers, Kiss rebreathers, Juergensen HammerHead rebreathers, Delta-P Sentinel and CCRB Ouroboros as well as old navy rebreathers such as the Mark 15, Mark 15.5 and Mark 16 rebreathers.

More importantly you’ll find expertise and a community which members will go the extra mile to help, offer advice.

Moreover members of RBW will alert you of ebay rebreather scams which are not uncommon. Also, if you’re looking for a rebreather, make sure you ask for advice here or on RBW; it’s a big purchase. Understand the pros and cons of each rebreather, make sure you buy a complete, factory overhauled, safe system and get proper training from a reputable instructor.

As fate has it, my next dive was blown out and I am traveling to Europe all of December. We’ll have a review for you guys ASAP though. Stay tuned!

Unfortunately, this rule of thumb is completely useless when it comes to dive planning. The trouble is that it doesn?t answer the question, ?At what tank pressure do I need to leave the bottom??Think about it for a second. Why do I care about how much gas I have left on the surface? There’s an unlimited supply of it up there! What I really care about is how much gas I have underwater and how much I need to make it back to that unlimited supply without getting injured or drowning!

Consider this realistic emergency situation:

You are happily diving along at 100 ft when a team-mate comes up to you, panicked and completely out of gas. Being a good team-mate, you donate your regulator to him and sort out the situation. Both of you are diving typical single aluminum 80s. You look at your pressure gauge and see that you have 800 psi remaining. Is that enough gas to get you and your buddy safely to the surface? How do you know? What are your options? Do you have enough gas to start swimming for the anchor line, should you begin a safe, controlled ascent now, or do you need to bolt for the surface as fast as you can?

To answer this question, before entering the water we must calculate something called Rock Bottom. Rock Bottom is the minimum amount of gas required to get two divers safely to the surface from the maximum depth including a controlled ascent (maximum of 30 ft/min ascent rate) and safety/decompression stops. With proper planning, just because one diver is out of gas is no reason to blow to the surface or eliminate safety stops!

Rock bottom must never be exceeded! It is the absolute minimum gas reserve that is required to safely ascend with an out of gas team-mate. If a team member reaches rock bottom, the dive is over then and there, without question or debate. Remember, the gas on your back isn’t just your gas, it is also your team?s gas and conversely, the gas on your team-mate’s back, is also your gas.

Just a disclaimer here: you might die if you do this my way, and my description of Rock Bottom may or may not bear any resemblance to GUE’s version of Rock Bottom or Minimum Gas Reserve.

Calculating Rock Bottom

Calculating Rock Bottom for any given dive is really not that difficult, but there are a few pieces of information that must be collected before beginning.

1. Actual: capacity of our tank in cubic feet
2. Working: pressure of our tank in psi
3. Planned: maximum depth of the dive
4. Stressed: SCR (surface consumption rate) for each diver

In this example, we?ll be using a typical aluminum 80 tank which has an actual capacity of 77.4 ft³ and a working pressure of 3000 psi (it holds 77.4 ft³ of gas when pressurized to 3000 psi). For the sake of easier math, we?ll round the actually capacity to 80 ft³. In real life scenarios, you probably shouldn’t round up like that. We?ll also assume a dive with a maximum depth of 100 ft. If you don?t know your actual stressed SCR, 1 ft³/min per person is a reasonably conservative number for most divers and helps assist and encourage planning by making the math easier.Exact numbers are not necessary here; just close, but conservative approximations.

The first step is to break up the ascent into sections.For a 100 ft dive, given an ascent rate of 30 ft/min plus a 3 minute safety stop at 15 ft, this dive will have 4 sections:

1. 1 minute to handle the emergency at 100 ft
2. 3 minutes to ascend from 100 ft — 15 ft at 30 ft/min
3. 3 minutes at 15 ft
4. 1 minute from 15 ft to the surface

So, it will take 8 minutes to reach the surface.

Next, convert the depth ranges to depth averages in ATA (absolute atmospheres), where one ATA is equal to 33 fsw (feet of sea water).

1. 100 fsw/33 msw = 4 ATA
2. 100 fsw to 15 fsw = average of ~60 fsw = ~ 3 ATA. Because of the linear ascent rate of 30 ft/min, the average depth can be calculated with the following steps:
   

   1. 100-15 = 85 (starting depth minus target depth)
   2. 85 / 2 = 42.5 (divide by 2 to get average)
   3. 42.5 + 15 = 57.5 (~60)(average depth plus target depth = true average depth)
3. 15 fsw ~1.5 ATA
4. 15 fsw to surface = ~1 ATA

Now multiply depth * SCR * time to convert SCR to ft3 at depth.

1. 4 ATA* 1 ft³/min * 1 minutes= 4 ft³
2. 3 ATA* 1 ft³/min * 3 minutes = 9 ft³
3. 1.5 ATA* 1 ft³/min * 3 minutes= 4.5 ft³
4. 1 ATA*1 ft³/min * 1 minute= 1 ft³

Add this all together and we see that one diver will require 18.5 ft³of gas to reach the surface with a stressed breathing rate.For two divers to reach the surface using this ascent profile, it will require twice that amount, or 37 ft³ of gas.That is almost half the volume of an aluminum 80!

The last step is to convert ft3 to PSI.This is done with the following formula:

v/wv * wp

where v is the volume of gas (37 ft³), wv is the working volume of the tank (80 ft³) and wp is the working pressure of the tank (3000 psi).

(37 ft³/80 ft3 ) * 3000 psi = 1387 psi (~1400)

Rock bottom on a 100 ft dive with an aluminum 80 is 1400 psi.

Each time you calculate a new rock bottom (if the tank or depth has changed), write it down in your dive log or wet-notes so you have it for easy reference the next time.

So, was 800 psi in an Al80 enough to get you and your out of gas team-mate back to the surface safely with a 3 minute safety stop, under stressed conditions? Probably not. In fact, you should have started your ascent 600 psi ago, long before you had an out of gas team-mate!It looks like you don’t have the gas to make it to the anchor line, so you better start ascending immediately. Your team might be able to make a controlled ascent, but chances are that you’ll end up having to increase your ascent rate beyond a safe limit or omit a recommended safety stop as a result of not spending a few minutes planning your gas supply on the surface.

With proper gas planning and a little discipline to stick to the plan, you will minimize the chances of having to choose risking a decompression injury over drowning. It also helps with peace of mind knowing that you have enough gas available to handle the situation.

Editor’s note: We liked this article so much, we created a t-shirt with its theme. It’s simple, classy, you can wear it at a club or a black tie function:

This is another tip in the category of “what I wish I’d known” back when I bought my original scuba equipment. Your average dive magazine and dive shop are filled with ads for fancy jacket BCs that have all sorts of bells and whistles – sometimes literally! Yet every technical diver I know including myself uses a different system called a Backplate & Wing (or BP&W) that is both stronger and cheaper and easier to use. Why? Keep reading.

Jacket BCs

Jacket-style BCs are what you see most in recreational scuba diving magazines. A jacket BC is a nylon fabric vest attached to a plastic backpiece. The buoyancy function of the jacket comes from inflation cells usually located under the arms and up the back. You can attach a single tank to the back via an integrated strap. Jacket-style BCs are common items in your local scuba store and usually command an entire rack of hangers to themselves. Jacket-style BCs are what you would rent at a resort or in a PADI diving class.

What Jacket BCs do well: quick easy sizing

Jacket BCs come in sizes like S, M, and L. These three sizes will cover 99.9% of the human population and are recognizable by anyone that’s ever worn a t-shirt. Cinch the velcro cummerbun as tight as you can and presto! You’ve got a BC that pretty much fits with less than 30 seconds of hassle. This makes jacket BCs perfect for use in rental shops and resorts where stocking a large variety of sizes would be too expensive.

However, if you are buying your own BC you don’t care about needing to cover a large variety of sizes. All you care about is your size. You are not trying to open a rental shop. The ideal BC is one that fits you perfectly.

Why is fit so important? Jacket BCs are like an oversize set of pants you hold up with a belt: sure they cover your ass but you’re swimming (in this case literally) around inside of them. And in this case, you use them to attach all sorts of heavy equipment to your body. When under water, you want your tank and weights to be snug to your body so that they are not sliding around every time you turn or look around. A jacket BC cannot do this well.

What Jacket BCs do well: heads-up flotation on the surface

A jacket BC puts the inflation cells under your arms. This can be useful because you can super-inflate the cells on the surface and they will hold you in an easy vertical position with your face way out of the water. This is perfect for beginner divers where being under water is the “scary” zone and the surface is the “safe” zone. If they are not comfortable with a dive or if they need to discuss something with their instructor they can hang out on the surface in an inflated armchair.

Sounds good right? Forget it. The more diving you do, the more comfortable you become with being under water. The surface zone has breaking waves, boats with ladders that will whack you on the head, low-PO2 ambient air — all sorts of drawbacks! Who wants to hang out on the surface?

Plus, inflation cells under your arms get in your way when inflated. As your diving skill increases you will likely be taking more things underwater with you: cameras, lobster bags, extra tanks, scooters, or even an ironing board. Your chest and arm areas become your “work zone” for attaching stuff. You need to keep this area clean and not puffed-up with a vest.

Furthermore, jacket inflation widens your profile in the water. You want to be as streamlined as possible underwater so that you expend less effort (and consume less gas) when swimming and are less susceptible to the pull of current. The under-arm inflation cells on a jacket BC will scoop water when swimming and cause drag.

So if jacket BCs are so bad, what’s better?

Backplate & Wing

A backplate & wing (or BP&W) is a flat rectangular metal plate that you attach to your back using a nylon webbing strap. Buoyancy comes from a doughnut-shaped cell (the “wing”) that goes on your back between the plate and your tank. The whole thing resembles a parachute harness. If your local scuba store doesn’t carry plates or wings you can easily order them online.

What BP&W does well: fit

The harness on a backplate is designed to be tight. You should be able to stick a couple of fingers between your suit and the harness straps, but that’s it.

Under water this means you and your scuba rig melded together as one piece. If you tilt downwards to look under a coral head, your rig stays tightly in place and doesn’t flop suddenly forwards and whack you on your head (done that!). If you tilt to the side, the rig stays fixed in the middle of your back instead of sliding off like a deckchair on the Titanic. A nice tight rig means you stop thinking about even having a rig attached so you can start focusing on the rest of your diving.

What BP&W does well: simplicity

A metal plate to hold things, a nylon strap to attach it to your back, and one inflation cell — what could be simpler? The plate and strap are near-indestructible but if you need to fix something you can do it with parts from a hardware store. The entire setup is open and obvious.

Under water a simple setup is crucial because you need to perform actions quickly and get them right the first time. You can’t see your own body to guide your hands because the mask interferes with your peripheral vision. If you’re wearing cold-water gloves or a wet/drysuit you also don’t have your sense of feel and the dexterity required to grope your way though a complex attachment or piece of equipment. A plate & harness excels here because it’s as simple as possible, and no simpler.

What BP&W does well: strength

Extreme strength may not seem necessary for the beginner or intermediate diver. You’re not attaching two hundred pounds of steel doubles tanks and lead weight. However, it’s good to know that your standard harness and plate can easily do that if you need it. The plate is steel or aluminum. The harness is 2-inch wide nylon, sometimes stiffened with resin. Buckles and attachment points are stainless steel.

You may not need all this strength, but it’s there if you need it. Your standard jacket BC with velcro attachments and thin nylon fabric will tear or drop that underwater camera when you least want it…like on the deck of the boat when you’re getting out in heavy seas.

Technical divers will also site an additional list of reasons why a BP&W is better than a jacket BC, for example that it provides standardization of equipment so that buddies on a diving team are guaranteed to know their partner’s rig as well as they know their own.

What About Cost?

One of the things I like about diving is that good technical equipment often costs less than the highly-advertised gear you see in scuba magazines. Let’s see if this is true for backplates and jacket BCs too.

Jacket BC Costs

These prices are from LeisurePro. I tried to pick the model from each manufacturer that best represented a high-end recreational BC, the kind of thing you would want to buy for yourself (versus rent at a resort).

BP&W Costs

You can buy a backplate, harness, and wing separately if you wish. You can also often find them sold together as a package deal. If you buy separately, you should get a tank strap to attach the tank to your plate.

Total price of the average piece prices: $471!

However, you can also find some package deals, like these:

• ScubaToys BP&W package: $319
• Golem Gear BP&W package: $390

So, not only is a BP&W better fitting / stronger / easier to use than a jacket BC, it’s also equal price (or cheaper!). What are you waiting for?

Convinced yet?

You still have a few choices to make if you decide on a BP&W instead of a jacket BC. Some recommendations:

• Harness: “Hogarthian” or “Deluxe”? A Hogarthian (named for the diving minimalist William Hogarth Main) harness is the basic, simple harness. “Deluxe” harnesses take a Hogarthian one and then add plastic buckles and extra straps. In this case, simplicity is better. Go with a Hogarthian. If you really feel the need to pimp out your rig, you can get nice soft Polypro webbing for your harness (I like it myself).
• Plate: aluminum or steel? This is a weighting question. A steel plate is approximately five pounds more negatively buoyant than an aluminum plate. If you need a lot of weight to dive (e.g. for cold water and a drysuit) a steel plate will relocate the weight off your belt and into the backplate which will be much more comfortable. If you travel by plane to dive, get an aluminum plate.
• Wing: how many pounds of lift? For typical single-tank open-circuit diving a 35lb or 40lb wing is quite sufficient. You don’t want a ginormous 60lb wing because the excessive size will cause drag.

Note: I’m not a scuba instructor and I’ve never played one on TV. If you’re an instructor or diver with the experience to recommend something to the next generation of up-and-comers, what would you suggest they get when buying their own set of equipment?

The 10W HID I had bought was not very powerful of course but most importantly I didn’t think it would endure the rigors of diving around Boston but more importantly the way I treat equipment. There was too much potential harm that could come to such a light. Having to open the canister to remove and charge the battery, potentially damaging the (user replaceable) o-rings and compromising the water tightness of the canister, thus risking a flood, wasn’t desirable.

HID bulbs are notoriously fragile and I had heard horror stories. Moreover, used to quality chargers in electronics such as laptops, I was appalled by the build and functionality of dive light chargers, some didn’t even have charge indicators. They looked like a $10 Radio Shack power brick hacked into a battery charger with a pair of scissors, some masking tape and cheap components.

Determined as I was to find a tougher, brighter and better light, I set my eyes on the Titan Dive Gear HydroLights X-Series. Titan Dive Gear’s other line of dive lights, the SCULA, has a battery built into the light head but can also tether to a battery canister.

I bought the 25W X-series which uses 7 LEDs for its max illumination and 3 to reach a dimmer 10W like illumination. The 25W X-series retails for $1065.00 with the smaller of the batteries (lasts plenty though). LED lights are very tough as there are no bulbs to break and I feel fine throwing my lights in my dive bag with all my other gear. The X-series is built tough from the head to the cable (and connector) to the battery. In fact, each light is tested to 600ft for three hours in a water pressure pot before they leave the factory.

Let’s talk a bit about the connector and LiCo (Lithium Cobalt) battery canister. To charge the battery, you simply connect the charger directly to the canister. To use the light, you’ll connect the light cable to the battery on one side and to the light head. on the other. The battery canister doesn’t open and you don’t need it to. As you can see, it’s very foolproof. Also, when the batteries are fully charged, the LED on the charger will turn green. This might seem obvious but not all dive light chargers do that. Also, I find the Titan batteries to be exceptionally light and small for their capacity. In fact they’re so small that I prefer to stick the canister somewhere on my rebreather than on my harness belt. The magnetic switch on the light head (instead of somewhere on the cannister) makes that pretty easy.

I have been using my light for about a year now and it’s still going strong. I keep a couple of batteries around, one that lasts nearly 5 hours at 25W and 12 hours at 10 W. The other one smaller (they’re both small compared even to a 10W HID canister, not to mention the big 21W or 35W canisters) will last 8 hours at 10W and a little over 3 hours at 25W.

Still, no piece of gear is perfect so let me nitpick a bit:

• the 25W X-series head is a little on the bulky side, it doesn’t always balance well on your hand.
• the Hydro Light glove, a soft goodman handle does a decent job but it’s not amazing. Some will prefer a stiff goodman handle
• Spare parts for the X-series are available but a replacement 120W is $525, a spare cable is $120. On top of the $1200 25W X-series, grabbing a spare battery and cable brings the total cost to a whopping $1845. Because you have to pay for the canister on top of the battery element, spare batteries are more expensive than on a classic canister light.