Catalina + Equipment Testing


There are two types of technical divers. Those who “tinker” with gear constantly and those that … WELL, NEVER MIND, there is only one kind of technical diver….

This post will mainly be gear related, but don’t worry, there will be some pretty pictures with fish at the end!

I had a business / work related friend in town so we decided to get a couple dives in and I thought it would be a good chance to test some gear for a potential dive on the USS Hopewell (still not quite committed to that yet, but definitely considering it).

The original plan was to dive the Palawan wreck and then find something else. However, we’ve had some wind and rain lately so we figured that Catalina might be a better option than Redondo Beach.

Gear Testing

The USS Hopewell is a deep dive (about 400 feet to the sand) and so I needed to test a few pieces of gear before attempting it. In addition to some scooter / DPV modifications I need to do for cameras and lights (those are a still a work in progress), I also wanted to test three new things on dives that were in shallow depths:

  1. External Oxygen Bottle
  2. Bigger Drysuit Bottle
  3. Music!

External Oxygen Bottle

My rebreather is a rEvo and it has a feature called a “Constant Mass Flow” (CMF) valve — or what most people sometimes refer to as a “leaky valve.” That is a fancy way of saying that it is always adding oxygen into my breathing loop at a constant rate regardless of depth. For those who fancy a technical read, the inventor of rEvo rebreathers has posted an article about it.

I really like the CMF and plenty of other rebreathers have the same mechanism and it works for 99.99% of divers for 99.99% of their dives. In order for a CMF to function and deliver a steady supply of oxygen regardless of depth it basically “plugs” the pressure sensor on the 1st stage regulator so that it will deliver a specific pressure regardless of depth. Your body consumes oxygen at the same rate regardless of the depth you dive. That internal pressure (IP) is usually set to about 10.5 ATM which is equivalent to 9.5 ATM *33.3 feet = 316 feet.

It doesn’t matter if you are at the surface or 300 feet deep, the regulator will deliver a constant flow of oxygen of about 0.6 liters per minute.

Here is a picture of the oxygen 1st stage on my rebreather and you can see the stainless steel plug instead of the usual membrane (I know the picture says “Pout max 12bar” but it is usually set to about 10.5 and the leaky valve is set to deliver 0.6 lpm at about that pressure).

rEvo O2 1st Stage

As long as you stay above 300-ish feet, everything works great. But what happens when you go below that depth? The system stops delivering oxygen and that isn’t great. Given that the oxygen level is already elevated, nothing will happen for quite a while — BUT, you will start increasing your decompression obligation VERY quickly at that depth as your oxygen level decreases. Again, for almost every diver and almost every dive, this isn’t a problem.

I knew this would be a problem on my dive on the USS Vammen but I also knew that if I poked myself about that depth and added some O2 then I would be okay for a bit of time. It was also on the edge of that depth and I wasn’t too worried about it. The USS Hopewell is altogether different and I need a better strategy.

There are two or three options for doing that. After some research and thought and talking to other rEvo divers, I have decided on the addition of an external O2 source with it’s own regulator that is plugged into the manual add valve (MAV) block. This can then also act as a secondary oxygen source (added benefit) for deep dives in case my primary tank or regulator has a problem. I decided to use a dedicated 6 cubic foot tank that I normally use for adding air to my drysuit.

Here is picture of of the tank mounted to my rebreather along with the hose connecting it to the MAV. It is the small yellow tank on the left side of the unit with the black hose going to that block with other hoses connected:

Off Board Oxygen Setup

Next question: how do I test it?

I wasn’t going to do a 400 foot dive just to test the setup so I decided on an alternate plan. I would assume the regulator would work at that depth (Apeks makes great regulators and I have no worries about that). But, I would simulate that depth by shutting off my primary oxygen supply and then manually run my unit using the external oxygen source for 10-15 minutes. That is normally something that nobody would ever do. I had invited along DJ Mansfield who could keep an eye on me and re-verify my PO2 while he was diving his rebreather just as a backup.

The results: mostly positive.

The ONLY problem I ran into was that the hose I used was a bit short. In the photo above, it looks like it is the perfect length but when you put the rebreather on, that manual add valve block rides up on your shoulder and the hose I used was too short and pulled it off to the side. It wasn’t anything that was hard to deal with, but I’m glad I tested it and will use a longer hose when I need to actually use the setup.

Overall: Success

Bigger Drysuit Bottle

Since a drysuit is a closed system, when you descend the air in the suit collapses and you get “squeezed.” You can feel this almost immediately upon descending. There are a lot of ways of adding gas to your suit to counteract this effect. It also varies a bit depending upon whether you are diving regular open circuit scuba or a rebreather. It certainly varies if you are diving with helium for deep dives since helium is a really bad gas for insulation.

Generally, when I dive on my rebreather, I almost always use a small external tank with a small amount of gas (6 cu ft tank). The yellow tank that holds oxygen in the picture above is a 6 cu foot tank. Small and compact.

The problem is that on a deeper dive, you don’t want to run out of gas to add to your drysuit when you are really deep. There are ways to deal with that such as “plugging in” another gas that you carry for bailout but that is time consuming and just not something that you want to deal with at depth.

Normally, a 6 cubic foot tank would be “okay” for a 300+ foot dive and I used one on my Vammen dive. However, it leaves little room for error and I sometimes lose gas out of my drysuit for various reasons (all self-inflicted).

I recently bought a 13 cu ft tank to use for suit inflation and wanted to test it. This was an easy test and shouldn’t have caused any issues but I was also testing a new tank mounting system and so it was worth trying. You can see the larger silver tank on the right side of the rebreather in the picture above. I was testing the relatively new adjustable side-mounting bracket from rEvo pictured below on the tank:

As expected, it all worked well.


I’ve been working for a really long time on finding a way to listen to music while on deco. For a 30 minute decompression obligation, I don’t really care. For a 2-3 hour obligation in open blue water when there can be current and things can “suck” and there is nothing to do, I do care.

I know plenty of people who, on a cave dive, leave an iPhone in a waterproof case at 20 feet and then watch a movie with subtitles while decompressing. For a cave dive, when you literally lay on a rock or a tree stump during your long and last deco stops, this makes sense. For a dive in the Pacific where currents and conditions are unpredictable and can change and you are on a down-line, I’m not a big fan of watching a movie (although I have to admit I’ve considered it).

I’ve also heard about systems that can be dropped into the water from the boat but then everybody needs to hear me cranking up Ricky Martin on deco and I’m not sure my dive buddies want that!

On these dives, I tested leaving a “special” iPod shuffle on the line at 30-40 feet. Underwater Audio used to sell an iPod shuffle that had been “water-proofed” by adding some “goo” into it. They don’t sell it anymore and it used to say it was waterproof to a substantial depth but not anymore. It is also questionable about using it in salt water.

One of the issues I’ve found with this solution in the past is that you need to have an audio jack in the player to help prevent flooding and issues. This raises the question of how to leave it when doing a deeper dive? You can’t take the player with you on the deep portion of the dive so you need to hang it on the line somewhere and that means disconnecting your headphone cable from the player. In this case, you have an open audio jack which is problematic.

I had a solution: I would plug in an extension cable so that the audio jack on the player would be plugged up and then I would plug my headphones into the end of the extension cable when I got back up to the depth I stored it at. This conveniently solved another problem.

When I was in the Great Lakes I had tried to implement a similar solution in a different way. My plan on that trip was that I would leave the player with the headphones connected but stored on the downline. Then when I got to the deco stop, I would “simply” plug the headphones into my ears and listen to some sweet music on long deco. Wrong!

If you have ever tried using thick dry gloves to plug tiny earplugs into your ears under a 9mm wetsuit hood, I can tell you that it doesn’t work well. It was an exercise in frustration. Of course, I had plenty of deco time on the line to work on it, but I couldn’t get it to work so it was a frustrating deco to say the least.

Now I had the solution: Leave the iPod Shuffle on the line with an extension cable so that the headphone port would be covered and I would “pre-dive” plug in my headphones so I wouldn’t have to deal with trying to do that with dry gloves and thick hoods!

How did it work?

Well, on the first dive it worked very well. DJ took a short video of me rocking out while on deco:

Rockin’ In The Free World

On the second dive, there was a bit of a problem. We were on the Valiant wreck and on a mooring ball. Those mooring balls are attached to a big cement block on the bottom via a very large chain that is encrusted in mussels. Hence, finding a place to attache the iPod was very tough. I finally got it attached; however, in the process, the extension cord came out which left the headphone port exposed. I re-plugged the extension cable back in and figured it wouldn’t work again.

It actually did work on deco and then when I got back to the boat I had a decision to make: freshwater rinse and expose the headphone port again to remove any saltwater? I decided to go for it and dunked it for a good 20 minutes in freshwater with my camera case and it still worked when I got home.

Overall: Mostly a success but it is still a “fragile” solution and I need a better one

I also decided to use a piece of duct tape to keep the extension cable attached to the player. This is obviously not going to be a permanent solution but should be good enough to keep it attached until I get it placed on the downline.


As promised, here are some photos I took at both Little Farnsworth and at the Valiant. We had nice visibility on both dives.

Little Farnsworth

Little Farnsworth is on the East end of Catalina close to the Infidel wreck. It is a series of rock pinnacles that start about 80 feet deep and they are on a sandy gentle slope.


I’ve posted about the Valiant before so I won’t spend more time on that. We had great conditions and I spent some time working on highlighting the differences between natural light photography and artificial light. I think the best example of that is the comparison pictures below of the bow of the yacht.

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