Twinnies

[TSandM]

As you'll be dealing with an Oz dealer/distributer, I doubt it's worth worrying about

Kern, let me correct this. Oxycheq did not stand behind their dealers and distributors with the lights, either -- they left their dealers standing out in the cold when the lights failed, and they refused to make good on them. Having a good, honest distributor/dealer is NOT a guarantee against getting burnt. Ask my VERY good LDS about that . . .

Anybody who reads my posts knows that I very rarely say anything negative about anybody or anything. My experience with the Oxycheq lights, and worse, my good friends' experiences (where they were publicly TOLD to go away and stop bothering the company) put me off that firm for good.

 

[Kern]

Kern, let me correct this. Oxycheq did not stand behind their dealers and distributors with the lights, either -- they left their dealers standing out in the cold when the lights failed, and they refused to make good on them. Having a good, honest distributor/dealer is NOT a guarantee against getting burnt. Ask my VERY good LDS about that . . .

Anybody who reads my posts knows that I very rarely say anything negative about anybody or anything. My experience with the Oxycheq lights, and worse, my good friends' experiences (where they were publicly TOLD to go away and stop bothering the company) put me off that firm for good.

TSandM, I know what you're saying, & if I was in the states I wouldn't suggest otherwise. But we're in OZ. Dealers & distributers play the game or the full force of the law can be brought down on them via the ACCC. And as I said, we're talking metal plates & a very popular wing. I feel quite certain the OP won't have any warranty problems no matter what gear he decides on.

PS. Even Aqualung was recently forced to play the game our way. You can now by their gear over the net, & they can't fix prices.

 

[Lobzilla]

In as much as 300bar is the higher pressure, & 232bar is the lower pressure you're right. We just don't use the convention in Oz. In the US HP is about 232bar & LP is below 207bar, you'd be hard pressed to find a 300bar steel tank.

Everyone keeps telling you about the lousy Oxycheq customer service in the US. As you'll be dealing with an Oz dealer/distributer, I doubt it's worth worrying about. As we're talking about metal plates & one of the most popular wings around, I wouldn't worry about customer service too much.

If you just want to ponce about on rec dives in doubles, get an aluminium 80 & dive a wet suit. If you want to get some worthwhile bottom time on tec dives to 55mts, get a set of 12 x 232's & a dry suit. You're in Melbourne, it'll be cold at depth down there. Don't think redundant buoyancy, think about how a cold body can compromise your deco.

There is no cheap way to play the tec diving game. Get some reasonably sized tanks & a dry suit, & do it proper.

If you really go down that route you will have multiple tank sets before you know it. Tanks seem to multiply quickly when left alone.

However, the AL80s are by far the easiest tanks to get trimmed in if you are new to doubles. I was skeptical when they were recommended to me by a top-dog GUE instructor. I mean, how can two cheap reef-tourist tanks be of any use for tec diving?

Now, they are the baseline for everything bigger (Hp100s, Lp85s, and Hp120s soon) to be measured against in terms of 'trimability' and my first choice if ~150cf will do the job.

+1 on the drysuit.

 

[packeteer]

in AU it's usually either 232bar Faber steel or Catalina/Luxfer alloy tanks (not sure of pressure ratings).

I would go with double Faber 12's from here or here. Both about $400 each

As for the rest of your kit, give Chris at DiveTub a call. He'll give you good advice and will even lend you equipment for tryout!

ps. I have a Fusion dry suit for sale, size 2XL

 

[Ozgarr]

In as much as 300bar is the higher pressure, & 232bar is the lower pressure you're right. We just don't use the convention in Oz. In the US HP is about 232bar & LP is below 207bar, you'd be hard pressed to find a 300bar steel tank.

Everyone keeps telling you about the lousy Oxycheq customer service in the US. As you'll be dealing with an Oz dealer/distributer, I doubt it's worth worrying about. As we're talking about metal plates & one of the most popular wings around, I wouldn't worry about customer service too much.

If you just want to ponce about on rec dives in doubles, get an aluminium 80 & dive a wet suit. If you want to get some worthwhile bottom time on tec dives to 55mts, get a set of 12 x 232's & a dry suit. You're in Melbourne, it'll be cold at depth down there. Don't think redundant buoyancy, think about how a cold body can compromise your deco.

There is no cheap way to play the tec diving game. Get some reasonably sized tanks & a dry suit, & do it proper.

I agree completely with what you're saying. I'm opposed to diving aluminium doubles, and wish to purchase a drysuit with large steel tanks. But at this stage, I don't think you've fully justified their purchase in my mind. So I've attempted a last stand... Or something.

So here we go, a couple more questions...

I've done 60 minute bottom times in 12Celcius water, and emerged after the dive feeling positively toasty. Obviously, there will be various thermoclines in the bay, and it may get colder, and exposure may be longer with compulsory stops involved. But, when starting with tec, I'll be doing dives to depths of 45 msw with probably 15-20 minutes deco? Realistically, I won't be doing dives longer than one hour, and thus, will not require more exposure protection.

On the tank sizing... With a consumption rate of 16 litres per minute, diving 12L x 232 bar tanks would give me about 42 minutes bottom time at 55 metres, including a 50 bar reserve. Diving twin 10.5L tanks would reduce my bottom time by approximately 5 minutes, and would weigh almost 5 kilograms extra (27.4kg vs 22.6)! Surely, with my strength, this would be a more logical solution. However, I can understand if you're coming from the perspective of trim. A longer cylinder would surely perform better on a longer body...?
​

 

[Lobzilla]

Ozgarr,

Since you did not list your experience in your profile the following maybe totally obvious but I mention it anyway...

Here is what I discovered when moving to doubles recently.

A single tank can be moved up and down on your body to get the trim right. With doubles this is not possible (or only in a very small amount) since the manifold needs to be a little above your shoulders to be able to manipulate the valves.

There are very few people complaining about doubles (with drysuit) being tail heavy. Most folks fight head heavyness. Feeling that you are going over your head any second is almost as annoying as a flooded drysuit and you do not want to use 'hacks' like ankle weights.

Therefore, the tanks need to be chosen not just based on volume and availability but also based on whether they trim out on you. That means you can 'hang' in horizontal trim without moving your fins. While correct posture is an important factor for this, the tanks will at some point pose a limit how far you can nose down without loosing it. The closer you can get to zero degree trim comfortably, the easier all other maneuvers will be.

 

[Trace Malinowski]

Just wanted to clarify something Claus wrote about the position of the manifold. The idea position for the manifold is actually sitting right across the shoulders. When someone is standing in their tanks facing you, you shouldn't be able to see the manifold above their shoulder line. In the water, the head should be able to go all the way back through it's natural full range of motion without being prevented from doing so by the manifold. Ideally, underwater a diver's head will just barely contact the isolator knob when the head is extended as far back as it can comfortably go.

Since nothing is absolute, this is a good starting point for the position of your tanks with the upper bands right at the break of the cylinders. With the cylinders sitting in this position, they will better positioned to be in your slipstream reducing drag while allowing unrestricted head movement in a horizontal position. Some divers may need to adjust up or down from here depending upon their comfort, body type and flexibility. Adjustments can be made by loosening or cinching the harness.

BTW, Claus, PM me your current cert levels so I can discuss parallel training options. I haven't forgotten.

 

[rjack321]

Ozgarr,
Long before you have any business being at 55m you'll probably have more than one set of doubles. Your 16L/min consumption will hopefully drop, your reserve gas thinking will go up. And you'll figure out that the differences between 42min and 37mins at 55m are significant not just from a backgas persepctive but from a deco gas perspective.

I would go with the Al80s to start. They are cheap, easy to dive and can be turned into stages or single tanks etc as you progress.

 

[DwayneJ]

I would go with the Al80s to start. They are cheap, easy to dive and can be turned into stages or single tanks etc as you progress.

I agree and you can convert to singles and sling them for deeper dives when you migrate to CCR

 

[Kern]

I only supplied the info on the WP of the aluminium 80 as they aren't very common in Oz, & I thought you may not have seen one. This lower pressure by itself is really quite unimportant, they still have about 80cft of gas. I recommended 12lt x232bar tanks as they trim out very nice, for me, & can be used for a wide range of depths & BT's. If you are doing 45mt dives with 15-20 minute deco, the steel 10.5 x 232bar will be more than adequate for the purpose. The aluminium 80's would be too.

If you're nice & toasty after an hour in 12^oC water in a wet suit, maybe you don't need a dry suit. Then again, on deco dives ….. but each to their own. If you are going to stick with a wet suit with doubles, I would suggest getting the aluminium 80's over the steel 85's, & using a DSMB as redundant lift. Pulling myself up a string line from 45mt or more, while wearing steel doubles, just doesn't appeal.

As others have said, you'll probably end up with more than one set of doubles anyway, & 80's could always be pulled apart & used for stage/deco bottles at a later date.

Coincidentally, I use 16lt/min when planning gas consumption for deco dives even though my actual consumption rate is less. When planning rock bottom, I use a consumption rate much higher than 16lt/min. I like to know I'll have more than enough gas for those unexpected, & stressful moments, such as lost deco gas, a buddy with back gas problems, there's a lot more effort going into the dive than usual,etc.