Interesting results of recent dives

[Diver0001]

We've made a series of dives recently to try out different settings on the Suunto computers. We've only done this out of pure curiosity to see how these settings affect your dives in real world circumstances.

We're using a Gekko, a Vytec and D6.

We haven't applied any scientific method to this so don't expect too much but there are some interesting results that might be worth sharing.

Anyone familiar with the Suunto computers knows that they have 3 levels of conservatism; P0, which is the default, P1 which is more conservative and P2, which is the most conservative.

We've done a 1/2 a dozen dives recently with the computers in different modes.

The dive we've been repeating involves a descent along the bottom to a maximum depth of about 34 metres. We've been extending bottom time by 8 or 10 min beyond the point where the computer goes into deco mode and then ascending with the Gekko in different modes and using some small variations on ascent protocols.

To make comparison easy we've done all of these dives on air from start to finish. (I know... don't flame me) but they were planned and we have the training required for extended range diving (in other words, don't get yourself on Ridiculousness by trying this without training).

First, the "standard" P0 profile: After a few iterations, we're having the Vytec and the D6 go to into deco mode at about 18-20 minutes. The Vytec goes about a min earlier. We'll continue at 34 metres for another 8-10 minutes (give or take) and then start ascending. the ascent is 10m/min to 18m then a 1-2 min stop (in order to synch the computer with depth) and 3 m/min to 6 min. Dead slow after that, usually taking up to 10min to ascend from 6m to the surface after required stops are done. If you don't understand why we would ascend like this then I'm happy to explain it later.

In P0 the Vytec will be in deco mode until we've been at 6m for about 6-8 min depending on the exact profile of the bottom phase. The D6 will usually have about 2 min of deco left @ 6m, which we assume has to do with differences in deco model. The D6 probably gives some "credit" for deep stops, whereas the Vytec does not appear to.

The Gekko, which is the same vintage as the Vytec (ca.2005), and as far a I know has the same algorithm, is the computer we've been putting into P1 and P2.

In P1 the Gekko goes into deco mode shortly after reaching maximum depth. It also gives a longer last stop than it does on P0, so as soon as it enters deco you're looking at 7-8 min to ascend. It also accumulates deco faster than it does on P0. During the ascents we've been doing from these dives (which are not big dives), it will usually show up to double the amount of required deco that the Vytec does.

I'll spare you all the discussions but we've reached the conclusion that if you're diving in very cold weather, or you're not entirely fit or used to decompression diving that P1 is actually a better setting for small incursions into deco than P0.

On P2 it's ridiculous. During the descent, when passing 18m it's showing an NDL of 27 min. The PADI RDP for this depth shows 56 min. It enters deco before reaching maximum depth and immediately starts reporting a significant deco obligation. By the time the Vytec is showing 9 or 10 min ascent time, the Gekko is telling you 30 min.

Moreover, and this is counter intuitive to anyone who knows much about deco theory, when you ascend to 18m and start doing 1 min stops every 3 metres, it *continues* to accumulate deco time. The deco time only starts to decrease when you've reached about 12m-9m and by the time you've reached 6m it's still showing 30 minutes of required stops. What we found interesting was that the ceiling increased by 10cm at a time, instead of stepping up by a couple (2-3) metres at a time, like the tables or many software packages.

Getting back to the dive, during the same dive where the Gekko showed 30min of deco @6m with a ceiling of 3.8 metres, the D6 was showing 2 minutes of required stops at this depth and the Vytec (on P0) was showing 7, both with a ceiling of 3m.

We've done this a few times now and the relationship seems to be the same. The P2 mode seems to show triple the ascent time on the bottom, an accumulation of deco during an ascent when everything you ever learned about deco theory is telling you that you're off gassing and then by the time you've reached the 6 meter stop the deco obligation is 4-5 times longer.

Moreover, and this is a bit worrying, if you go above the ceiling then it enters error mode immediately. This is bad. Your deco theory tells you that within a certain range you should be able to descend back under your ceiling and continue your deco with or without a "fudge factor" to compensate for never having learned buoyancy control. The Suunto doesn't compensate for any of these practices. As soon as you go above you're ceiling then you're on your own.

Our conclusion is that we don't really see an application for P2 for normal healthy divers. I don't know what Suunto thinks about that so to cover my butt I should also say that THEIR opinion matters. Mine does not.

Just thought I'd post about this because some of these tidbits were new to us and I figure we must not be the only ones who where curious about it.

R..

 

[DaleC]

Good work Diver0001, I like a thread with some meat to it.

As a somewhat older diver I use a Gekko (on PO) knowing it's already a conservative computer. I'm ok with that as it works for the type of diving I do (shore diving with long SI's if needed). I don't have a problem with the deco obligations and have often accrued 10+ which almost always clears on the way up doing a gradual ascent. What is not so good is the penalties it imposes on repetitive dives. On a charter (where SI's are short) this can be a pita.

Some people rib me about the Suunto model but I don't really need to dive aggressive profiles. There is always another dive.

 

[boulderjohn]

Years ago I used a Suunto Cobra while diving in Truk Lagoon, and it somehow got onto P1. I have no idea how, and I did not notice it until I saw I was getting ridiculous deco requirements in comparison to other divers with Cobras (about 2/3 of the boat). Once I realized what had happened, I switched back, but it continued to punish me because of the history (I suppose). People were calling me "Captain Deco." I surmised that if I had accidentally put it into P2 instead, it would not have let me out of bed.

Moreover, and this is a bit worrying, if you go above the ceiling then it enters error mode immediately. This is bad. Your deco theory tells you that within a certain range you should be able to descend back under your ceiling and continue your deco with or without a "fudge factor" to compensate for never having learned buoyancy control. The Suunto doesn't compensate for any of these practices. As soon as you go above you're ceiling then you're on your own.

I have written about this feature of Suunto computers before. I see it as a serious flaw, and I wrote to Suunto to tell them that. They stoutly defended the practice, but I found their reasoning so ridiculous that I don't even remember it. I have written about this on ScubaBoard before, and the practice has been defended by other posters. As far as I could understand their reasoning, they are saying that you are going to die anyway, so there is no point in having the computer continue working. (OK, they don't put it quite that way.)

My experience with this was with the new HelO2, their flagship tech computer. My buddy on a dive had just gotten it on a key man discount, and he wanted to try it out. We did a dive according to V-Planner, and we followed the ascent plan perfectly, just observing what the HelO2 did as we ascended. He had set up the HelO2 in a way he thought should be similar to V-Planner. It started getting very angry with us with about 4 deco stops to go, and it went into error mode during our 30 foot stop, with nearly a half hour left in our ascent plan. We were using it as a backup to the V-Planner schedule, but a computer that quits like that is not much good in that role.

In comparison, I later did exactly the same thing on a similar dive, following a V-Planner schedule and observing what a Shearwater Predator did. I had made no attempt to make the Shearwater's Buhlmann algorithm match V-Planner, and when I checked its intended plan before the dive, I saw that it was very different from what we intended to do with V-Planner. As we ascended, the Shearwater kept telling me to do something different, but it also kept adjusting and trying to guide me. Amazingly enough, the Shearwater cleared me less than a minute after we completed the V-Planner schedule.

I generally think that a computer that keeps working for you and keeps trying to guide you safely to the surface no matter what you do is more valuable than one that quits when some circumstance in your dive puts you off schedule.

 

[Diver0001]

My experience with this was with the new HelO2, their flagship tech computer. My buddy on a dive had just gotten it on a key man discount, and he wanted to try it out. We did a dive according to V-Planner, and we followed the ascent plan perfectly, just observing what the HelO2 did as we ascended. He had set up the HelO2 in a way he thought should be similar to V-Planner. It started getting very angry with us with about 4 deco stops to go, and it went into error mode during our 30 foot stop, with nearly a half hour left in our ascent plan. We were using it as a backup to the V-Planner schedule, but a computer that quits like that is not much good in that role.

A buddy of mine has this computer and it routinely makes stops that are deeper and longer than one would think is logical, even from relatively tame dives. It appears to start making a 1 or 2 metre / min ascent quite deep, speeds up through part of the ascent and then gives credit for that weirdness when you get shallow. No other bubble model that I'm familiar with makes required stops that deep or slows your ascent that much or punishes you as severely for not doing as you're told. It initially made me wonder if there wasn't a bug in the software.

On the other hand, it would appear to be the case that this computer does generate a valid ascent through to 6m. That said, I really don't think that giving shallow credit for spending more time deep is telling the whole story. I think that we don't have enough evidence yet to support the conclusion that Petri dishes, which is where the vast majority of evidence for bubble models has been collected, are a good analogue for the human body.

I don't mind following a deeper ascent curve and I do accept that there is some evidence to support that deep stops can limit bubble growth, but I'm reluctant to cut the last stop or 2 short of what a Buhlmann model would give.

I generally think that a computer that keeps working for you and keeps trying to guide you safely to the surface no matter what you do is more valuable than one that quits when some circumstance in your dive puts you off schedule.

Yeah, throwing in the towel at the first sign of trouble is a nice CYA for the manufacturer but as a diver in the water the manufacturer's paranoid liability phobia isn't really your primary concern. There has to be other ways for manufacturers to protect themselves from frivolous lawsuits from Darwin candidates than to potentially screw every diver who uses one of their computers.

R..

 

[Blackcrusader]

I did not want to start a new thread and this one seems to be what I want sorry for what some might call a grave dig.
Just back from Bali doing mostly 2 dives a day. Most dives around 55 mins. We are on Nitrox 32%

My last two dives I am like bugger this I will just hang out a bit more not quite square profile. My guide is using his Suunto.
Anyway first dive goes OK no issues. We are in Padang Bai and the last dive is at the Drop Off a really nice almost wall dive.

On the second dive you can see where I show 35 minutes into the dive. My guide signals that his Suunto is low on NDL time remaining. I'm like ok see you I will continue on at this depth and you can ascend to add NDL time. I still have 49 mins NDL left lol

Now we had 20 hours surface interval to first dive and 63 minutes SI to the second dive. None of these are deep dives relatively shallow. I've always had fun when doing 3 or 4 dives a day and a guide uses a Suunto and NDL times are so different. Yes I run GF 95 for NDL dives. Maybe the guides are even on a conservative setting in the Suunto. The lowest NDL I had on that dive was 40 minutes.

So in the end we meet up for the safety stop. Nice thing was the last few days the guide was finding out that I would find critters he had not seen. He is looking at my TG6 photos on the boat after the dives.