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Discussion in 'Computers and Technology' started by Chris Richardson, Nov 10, 2020.
We did keep telling you.
What really did it for me was two 55m dives which I wanted some decent bottom time, so used a bottom stage.
Struth, the kit... A 12 litre twinset, three ali80 stages containing backgas (think it was 20/40), 50% and 80%. The gas bill for two dives was over £200! And jumping in with something like 100kg of kit. The boat was doing three days out of port, so I ended up taking two twinsets and five stages. I couldn't get the trolley up the ramp at the marina - needed someone to help push the sodding thing! All the others on the boat were doing 3 days, I could only do 2 because of the gas requirements.
Now contrast that with the rebreather... Firstly I'd easily be able to do three days with the oxygen and diluent lasting for two dives. I'd probably bring a spare set of O2 and diluent tins for the third dive, and two ali7 stages (for 55m and extended bottom time I'd probably use a pair of ali80s). Oh, and a small container of lime/scrubber.
Total running cost for the three days on a rebreather is around £40 (that's the oxygen, diluent with lots of helium and scrubber lime).
One thing I'd add, there seems to be a lot of talk about eventually doing technical dives. I've no idea if that's your intention, but if it is something you might consider in the future, a cheap nitrox computer that can be used in gauge mode, with tables is worth looking at. I have a suunto vyper which I bought used 10 years ago and I still use it in gauge mode as a back up to my ostc.
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What are peoples opinions on the Mares Smart? It does two gases, think it does Deco dives...? Don't think I'll progress to bring a tec diver, but in saying that I don't actually know what the differences between rec and tec are?!
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Recreational diving is all about diving to the NDL (Non-Deco Limits) tables (PADI words). These allow a maximum of 20 minutes at 30 metres when breathing air and a mandatory 3 minute safety stop.
If you want to extend your diving beyond this limit, you will have a decompression obligation, which is a virtual "ceiling" above you where you have to wait at that level whilst you off-gas. There's tables to calculate this, but virtually everyone uses a computer to work this out for them.
For illustration, a little dive planning example. A 30 metre dive on air.
20 mins bottom time using the PADI RDP (recreational dive planner) means you can ascend to 5 metres and must do a 3 minute "safety stop", so arrive on the surface at 20mins + ascent time (~3 mins) + safety stop (3 mins) = 26 mins underwater.
A 40 minute bottom time would require some decompression. Plugging this into the MultiDeco dive planning software:
Bottom: . 30m for 40mins (40mins elapsed)
Ascend to 12m in 2mins (42mins elapsed)
Stop at : 12m for 1min (43mins elapsed)
Stop at: . 9m for 4mins (47mins elapsed)
Stop at: . 6m for 35mins (82mins elapsed)
Total dive time 83 mins
This shows you that your 40 min dive has accrued 40 minutes of decompression, stretching out to 83 minutes underwater. Your air supply needs to be much bigger -- you will need a twinset and you must keep below those stop ceilings otherwise you'd get bent (DCS, DCI). Hanging around for that amount of time needs the buoyancy skills to stay at that level.
This decompression time can be significantly shortened by using oxygen-rich gas, called Nitrox, for example 32% oxygen (instead of air at 21%). This will leave you with a 12 minute decompression stop at 6 metres, a total dive time of 56 mins. Nitrox is very popular because it extends your bottom time.
This decompression time can be further shortened by taking a second cylinder of very rich decompression gas (for example 50%) which you switch to at the appropriate depth. The problem with the rich gasses -- which you will learn about on a Nitrox course -- is that inhaling oxygen at too deep a depth can kill you, the maximum depth for 50% is 21 metres.
Anyway, this is why having two gasses is useful. The first one is your bottom gas; air, 32%. The second one is your decompression gas, say 50%. You need to be able to switch to that gas underwater and you need to be able to take enough gas such that if one fails, you can get out of the water without being bent.
All these calculations, rules, equipment and procedures are why they call it Technical Diving. It's not for everyone, but it does mean you can go deeper and stay down longer.
Right, makes sense. So non Deco dives = rec and Deco dives = tec. Didn't know that was the differentiator.
In my mind I had imagined doing Deco dives, so if that happens I will be tec diving. I don't imagine that will be anytime soon though.
I'm surprised at how long the 6m Deco is without EAN!
So from reading other posts around planning dives, I'm guessing that's the reason the algorithm used in your dive computer needs to be 'open'.
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Not quite correct. That's the PADI model where you pay to take each step. However, in the BSAC world life is a little less transactional .....
BSAC Sports Diver, a recreational certification, permits diving to 35m with a significant decompression requirement for those completing the course. As I recall 25minutes decompression is the limit, if the diving is done according to BSAC 88 tables.
As a sports diver, and later as a diver leader I did quite a few recreational dives involving decompression before I started doing dives I'd consider technical diving. I think the introduction of helium is probably a realistic measure for the transition to 'technical diving'. If you make that transition then save time, and a lot of money, and get a rebreather!
The early decompression stops are fine as the focus is on being ready to move to the next stop. However, as the stops become longer life starts to get dull. That is why some of us have mp3 players. Listening to Portishead Glastonbury set at 6m can make the need to rush to the surface seem less important....
Does completing the BSAC Sports Diver certification involve twins?
haha, could do with an underwater tablet with Netflix
You mean if/when I reach that point? And why, is that because of the cost of the gases?
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Agree with Dave on this.
I started off in the PADI mould and didn't move to BSAC, so we've got slightly different slants on it.
In the PADI world which tends to revolve around the commercial local dive shop selling courses, the line between Rec & Tec is simply no deco (ignoring the safety stops - that's not deco, oh noes... ). Going past 40 metres basically mandates decompression, so there's a simple 40m bottom limit too. The main reason for this is that in order to do decompression stops you absolutely need the skills to be able to hold that stop. Having a very simple 'no deco' mantra supports that.
BSAC's much less commercial and based around the club with a steady progression through the grades. They tend to support you a bit more too, although that's very much down to the individual club (be that PADI or BSAC -- there's knobs everywhere!).
The useful thing about the PADI fold is as the relationship's more commercial, it's less of a problem to switch around. Although of course it depends on the club. It does work the other way too -- I fell out with a PADI club because I wanted to do more challenging diving; just didn't fit into their culture.
As far as PADI's concerned, they'll flog you the three main courses Open Water, "Advanced" Open Water and Rescue Diver (probably their best course - if you're PADI you should definitely do that course when you're ready). They'll also try to flog you "specialities" such as drysuit, peak performance buoyancy, wreck diving, deep diving, putting up an SMB, yada yada yada. They're not bad per-se, but it does seem like it's milking the customers and card collecting.
I'm quite cynical about PADI's "Tec" courses as these are frequently taught by Recreational DiveMasters who's entire technical experience was doing the course, as opposed to people who regularly dive well beyond the recreational limits. Walk the walk, not talk the talk.
Kind of brings on the instructor discussion... You need an instructor that you get on with and who has great standards. In the early days it's less important, but as you move on to more difficult things it becomes essential.
Ignoring the current lockdown mania, there's little question in my mind that learning to dive in benign warm + clear water, e.g. Spain, doesn't really prepare you for the challenging conditions you find in UK waters (dark, cold, tidal, rough water, poor visibility, predominantly wreck diving). However, learning in the UK means diving over "there" will be so much easier.
Just picking up on your algorithm comment - open. If you mean easy to access , manipulate conservatism, easy to use with a planning tool then yes. There are some like ostc computers which are open source so if your so inclined you can dabble with the software , even write your own.
So computers like sunnto using there own algorithm and planning via their own software leaves you feeling a bit blind to what’s going on. Hence these type of DCs tend to be very popular in the recreational diving but once into significant deco dives their not popular at all.
DCs from shear water , ostc and others will offer algorithms from buhlman and others where conservatism can be more personal , usually through gradient factors and planning is far easier through manufacturers software but also stuff like multi deco, Baltic (app) again where you can personally influence margins.
Gradient factors (GFs)-simply a way of layering your own conservatism over the straight buhlman table. Expressed as a GF low , this defines where you begin your decompression stops , the lower this number the more conservative and you’ll start stops lower in the water column. Then we have GF high , this affects the tissue loading when you exit the water. So a lower number will keep you in the water longer but you’ll exit with lower tissue loading. The higher the number the greater the tissue loading , 100% being the theoretical limit you can exit without going bendy.
So a GF of 50/85 will stop you deeper and hold you shallow longer than 90/95 which would push you shallow and out quicker but close to the theoretical dangerous bubble formation.
Hope that helps
Not specifically, although some sports divers do have twinsets and there is also a BSAC Twinset course. It is quite comprehensive and anyone recognised as a BSAC Twinset instructor (like me) can deliver the course. There's more about it on the BSAC website.
For most recreational diving there is limited advantage to a twinset over a single tank, with optional pony/stage, and it is a lot of more weight to haul around. For most diving it simpler to use a single tank and swap cylinders for a second dive.
If the gas planning for the first dive exceeds a single tank then a twinset may be worth using but that often that leaves insufficient gas for a second dive. In my twinset days I took a 300 bar cylinder of rich nitrox (40%) for decanting into the set for the second dive. Some people diving independent twins would breathe one down more and swap that cylinder for the send dive.
You might never go there. Most divers have no need for technical diving. Similarly, most divers have no need for a twinset. A twinset is an expensive change from a single tank and BC. Apart from bonkers stuff underground, IMHO, any dive best done on a twinset is probably better done on a rebreather.
Unless the diving requires it I'd steer folk away from technical diving. It can easily be the start of a slippery slope to having a garage with more dive kit than some dive shops!
A twinset is expensive, helium is expensive, for deeper and longer dives a more expensive computer is needed, a better torch, more cylinders and regulars, a scooter, another twinset or two and so it goes on.
If all that is being assembled then the initial cost of CCR isn't huge and the long-term benefits are massive. As a CCR diver (I still use single tank too) I have more flexibility, my gas costs are quite low, and I can spend a long time underwater without any concern about running out of gas. On my first trip to Malin Head (in 2010) my gas costs for the week were £500 (twin 16s and 2 stages) whereas my CCR buddy spent £30 on oxygen and used a couple of 3l bottles of trimix he'd taken with him.
With a CCR I can use the same gas for a 60m dive or a 30m dive. If I had a twinset filled with gas suitable for a 60m dive I'd be reluctant to use that on a 30m dive (I ended up with 3 twinsets). If I did a 45m on CCR then for a second day all I'd need to fill is my SMB bottle. With a twinset I'd have to get it and my stage(s) filled and out of gas is a realistic possibility if I overran my plan..
However, single tank diving is so much simpler and is plenty of complexity for most folk and I still enjoy the simplicity of it.
As you do more challenging diving — deeper, decompression obligations, overhead environment, etc. — then you cannot simply bolt to the surface. You’re now far more reliant on your dive kit to keep you alive and your kit needs to provide redundancy. You then need a redundant gas source such as a twinset, sidemount or a pony cylinder, or in the case of a rebreather you’ll take bailout cylinder(s). Similarly with your other kit; two SMBs, spare mask, two computers, two cutting devices, etc.
Your dive planning also factors this into the calculations, planning for one failure which means being more conservative.
With all this additional kit, you need the skills to use it; swapping masks, shutting down valves, changing regulators, putting up a second SMB because the first one tangled on the line and the reel is now on the surface, etc.
Thus 'rec' v 'tec' is a bit of a continuum where you progressively build up your skills.
Back to the original question, I have dived both the Suunto Zoop and the Mares Puck Pro (and currently dive with a Ration iX3M).
I much preferred the Suunto, I just found it nicer to use including setting a nitrox mix.
That said the colour screens on the latest generations of computers, Shearwaters, Ratio, expensive Suuntos are just amazing and if you have the money make a dive more pleasurable.
One of my buddies had a LiquiVision Zen with a failing screen and in shallow water he glanced at my Ratio as the screen was clearer from a distance than his was close up.
He has in fact just gotten himself a Ratio in a black Friday sale.
On recent dives I have been with people who had Shearwaters and Suunto Eons, and if I didn't have one (especially as someone doing recreational/entry level tec. diving) I would be happy with any.
As someone going tec. I would probably be picking between the Ratio and a Shearwater, but I believe that some of the Suuntos can now use the standard algorithms and if that is the case I wouldn't rule them out either.
It's user interfaces that count. The Shearwaters just work and are consistently intuitive, which is vital when you're messing around changing gasses.
Suunto's interfaces are awful and they have bloody stupid conservatism built in, such as their calculation of MOD for a gas where they take off 2% for the hell of it (e.g. 28% at 1.4PPO2 = 1.4/.28 = 5 = 40m, but not on a Suunto where it'll be 38m). This is bloody annoying when switching to Oxygen at 6m (1.6 and a ceiling of 6m) where the Suunto needs you to ascend through your ceiling to 5m to make the switch, then you can get back down below the ceiling.
Also Suunto's have ridiculous locks. Bend a Suunto, i.e. it's ridiculously conservative additional stops -- with the Suunto most aggressive setting -- are at least 10 mins later than Buhllmann has cleared from a deeper dive. If you think of getting out 1 min before its deco has cleared then the Suunto locks up for 48 hours -- and keeps locking up if it's put back in water.
When I first got the D9tx I went on holiday and tried it in the swimming pool. I switched it to gauge mode and jumped in. I then discovered that you cannot switch out of gauge mode into dive mode for 48 hours. Tried it at 46 hours and it locked me out again for another 48 hours.
Oh, if you forget to turn on a particular deco gas and jump in, the Suunto won't allow it to be used (yes, don't be silly, but easily done)
Am not a fan of Suunto for tec diving (as in deco or deep). Am happy to recommend their entry-level ones though.
Shearwater uses pretty much the same UI for all of their models (although I've not seen a Periguine yet). I've used a Perdix standalone for over three years on open circuit and moved to CCR where the Revo has a Petrel CCR controller and a Nerd CCR. They all use the same UI, but with additional screens of data. There was no learning curve at all. Also they use a single AA battery in the Petrel and Perdix which lasts ages and can be bought even in the back of beyond.
Another important thing is all the additional pieces of info available on the Shearwaters -- something to check over whilst on a long decompression hold. These include info such as the current Gradient Factor if you left to the surface now (could be important if low on gas); the delta5 meaning how much extra dive time would be added if you stayed at the current depth for 5 more mins (e.g. a sign of on or off gassing); GF99 which gives an indication of the min time you need to stay down. You can change gasses underwater, so if you forget to turn on a particular deco gas you still can.
TBH there's a reason why Shearwater computers are probably the most popular technical and CCR dive computers these days.
I don't know about the Ratio computers, but hope they're more like Shearwater's interface. I believe the OSTC has a similar interface to the Shearwater.
For the OP either of the options the suggested would suffice and there is no reason whatsoever to suggest a Shearwater would make any sense. A second hand Suunto with 'only 6' dives would also be fine but I sold that last year.
@Wibble the big issue with dive computers is choosing one suitable for purpose, knowing how it works (RTFM), and working within the constraints of thet computer. If it isn't doing what you want it to do then you made have made some poor choices.
Also, all the features you attribute to the Shearwater have been in my OSTC for years, possible from the day I replaced my last VR3 with one. The OSTC interface is nothing like the Shearwater (and even includes a few suggestions from me) and there is a reassuring alternative GF options for that 'moment' where surfacing is more urgent than deco and GF100/110 seems a fair choice, should it ever happen.
I do find them broadly similar but I guess most 2-button computers would have a similar structure (a 'next' button and a do/yes button). I do prefer the UI of the OSTC though but this might be because I used an OSTC before I used a Shearwater, if I tried a Shearwater first I may have preferred that.
My bitching's more about a four button interface that includes short and long presses, so an eight button interface.
Nobody every became more intelligent when underwater, certainly not me. So trying to remember the 'spell' to change gasses is irksome to say the least (long press on the bottom RH button; short press on bottom RH to select the gas; short press on top LH button to select it -- if you're above their MOD limits).
The OSTC and Shearwater's bleeding obvious and it's easy to see.
As interesting as this thread is, the OP stated that he was looking for a basic computer and was not even wanting to move to nitrox yet. Talking Tec computers is fun, but not answering the question.
A basic computer: I'd say get one that does Nitrox, like the Zoop.
Nitrox is fantastic for recreational diving, either allowing you to extend NDL dive time or increase the DCI safety margin. I'm surprised that more agencies don't teach it at an entry level.
If you're never going to use Nitrox, then you could get an "air only" computer, but personally, I'd prefer the future proofing of being able to use it in future.
My first computer was an Apeks Quantum, which is similar to the zoop I liked the extra benefit (and for me, future proofing) of being able to switch gas (if using a decompression gas) although once I started doing that, I changed computers to an OSTC. (I know - I should get a rebreather!)
Yep, a basic nitrox computer is all most divers will ever need.
BSAC may be odd in some ways but teaching nitrox from the entry level is definitely the way to go.
(see my comments at the end)
My first computer was a Suunto Vyper (like a zoop with a serial interface to upload dives to SDM3). It provided a single nitrox mix (no switching) and was bought with a full set of kit from the local dive shop (in 2006) when I knew I was hooked on diving.
I was doing fine sticking to the safe and sensible recreational stuff diving my Vyper in the nitrox mode until I was led astray by a reckless CCR diver and I found myself diving the Salsette on 26% and narked at 42m unable to comprehend what my SPG was telling me. I sometimes think the sensible action would have been to back off and focus on recreational diving, teaching people, NAS, Seasearch, and being a sensible and happy recreational diver in my BSAC club (I was even DO at the time).
However, instead I found myself drifting away from club diving and a helium grew and the Vyper was switched to gauge mode to be superseded by a VR3, and then another VR3 (people were selling them cheap and I couldn't be bothered with tables and slates) but I kept taking the Vyper to record the dives. After Malin Head CCR happened and I got my first OSTC and now have the OSTC cR.
The last wreck dive the Vyper recorded was the Salsette and now it has gone to a new life with a new diver starting out on their adventure but with a computer with a history they'll lever know....
The moral of the story is buy a basic recreational dive computer and limit the diving to the computer capabilities and save yourself a bloody fortune!!!