Frustrations with Suunto RGBM

[loosebits]

Taking my Vyper down to Coz always gives me a headache. Often on the 2nd dive for the day on a long dive series, it will be within a few minutes of going into deco. When it gets down to 1 min, I ascend a few feet and it then shows 3 mintues (lather, rinse, repeat) however by the time I get within saftey stop range, I am no where near the NDL.

I played around with the dive sim function and I noticed I could rack up a small amount of deco (10 mins perhaps) and it would clear before I brought it up to the ceiling.

What I would expect (and want) from a computer is that when it tells me I need 10 mins at 10', that means 10@10' if I start up right now at a 30'/min ascent rate and if I piddle around or ascend slower, that time increases. In other words, don't tell me I'm in deco until I'm at the point where the computer won't clear by the time I hit the ceiling if ascending at 30'/min.

While writing this question, I think I figured out why it can't do that (since it will allow me to do 12@15' or something like that, it has to recalculate and credit me during my ascent).

I guess what would be nice in letting me figure out what it's doing and allow me to gauge if the deco will clear by the time I hit the ceiling is to tell me which compartments are causing the deco (as a practical matter, this is probably too much info for the average diver to deal with). If it's the faster compartments, it will likely clear before I hit the ceiling, if it's the slower ones, it probably won't.

Does anyone intentionally let their Suunto's go into a small amount of deco knowing it will clear before hitting the ceiling?

 

[fdog]

Don't own a Suunto. My Aeris Atmos 2, however, will show me at the verge of deco (maybe a minute or two remaining), and an ascent will not begin to show time credit until quite shallow. So the behavior is the same, just different in magnitude of application.

I dive a computer to get credit for multi-level diving in this fashon.

Conservatism of the model is what kept me from using a Suunto for rec diving.

Can't say about deco, as all these are planned, and use cut tables.

All the best, James

 

[SeaJay]

Same thing has happened to me.

It got so annoying that I just put it in guage mode and planned my dive and dove my plan. I know that seems horrible to do to a couple-hundred dollar investment, but the Vyper still has some great functions... It still tells me my ascent rate, logs my dive for graphing later, and gives me all sorts of info on my wrist - including water temperature, dive time... Well, you already know. The only difference between guage mode and "AIR" or "NITROX" mode is an NDL.

...Which, as you've discovered, isn't really an exact science anyway.

Put it in guage mode. Plan your dive and dive your plan so that there's no confusion. How are you handling these jumbled numbers at depth anyway?

If you want more bottom time, the key is not to buy a computer that's going to squeeze another few minutes out of an NDL because it's "real time data" vs. "square profile." The key is to get more gas down there with you and learn proper decompression techniques. Do that, and you can choose whatever bottom time you like... No limits.

 

[Snowbear]

I guess what would be nice in letting me figure out what it's doing and allow me to gauge if the deco will clear by the time I hit the ceiling is to tell me which compartments are causing the deco (as a practical matter, this is probably too much info for the average diver to deal with). If it's the faster compartments, it will likely clear before I hit the ceiling, if it's the slower ones, it probably won't.

Looks like someone would greatly benefit from instruction in decompression physiology

 

[diverbrian]

Same thing has happened to me.

It got so annoying that I just put it in guage mode and planned my dive and dove my plan. I know that seems horrible to do to a couple-hundred dollar investment, but the Vyper still has some great functions... It still tells me my ascent rate, logs my dive for graphing later, and gives me all sorts of info on my wrist - including water temperature, dive time... Well, you already know. The only difference between guage mode and "AIR" or "NITROX" mode is an NDL.

...Which, as you've discovered, isn't really an exact science anyway.

Put it in guage mode. Plan your dive and dive your plan so that there's no confusion. How are you handling these jumbled numbers at depth anyway?

If you want more bottom time, the key is not to buy a computer that's going to squeeze another few minutes out of an NDL because it's "real time data" vs. "square profile." The key is to get more gas down there with you and learn proper decompression techniques. Do that, and you can choose whatever bottom time you like... No limits.

I very seldom need to worry about small deco obligations. They are planned, but I don't use gauge mode on my VyTec and don't plan to start unless I take a class on helium for which the Suunto's don't have a model.

I pay minimal attention to NDL's, but especially in warm water I do pay attention to them. I like to get more than one dive in per day and like to account for that residual nitrogen without having to worry about tables and arithmetic (I am great at math, lousy at arithmetic, LOL).

The other issue is that doing two or three dives per day on one fill of my dual 100's, I will run into gas limitations so I have to break my dive plans into shorter dives and follow that or I won't have enough gas to do more dives. Again, it is difficult in cold water and heavy gear to incur a huge decompression obligation that way. If I am doing a planned decompression dive, most of the time I have tables cut and key numbers written down on my wet notes anyways.

In short, I always considered the conservatism of the Suunto's an asset, not a gripe. If I am diving a computer, I would rather have one that puts a couple of more limits my bottom time than one that will "allow" (notice the quotes, I don't treat the computer's numbers as gospel. I add conservatism on top of the computer's.) me to push myself closer to being a pretzel.

Looks like someone would greatly benefit from instruction in decompression physiology

That too!

 

[ScubaRon]

Quote:
Originally Posted by loosebits
I guess what would be nice in letting me figure out what it's doing and allow me to gauge if the deco will clear by the time I hit the ceiling is to tell me which compartments are causing the deco (as a practical matter, this is probably too much info for the average diver to deal with).

The Pelagic computer's bar graphs do exactly that. It won't help you with your "problem" though.

 

[cortez]

Loosebits,

As I think you already figured out, and have heard from others its not just the Suunto RGBM, its the constant recalculation of nitrogen loading that changes deco obligations throughout a dive. I find myself more and more leaning back to what SeaJay said. Use the tables, plan your dive and dive your plan.

If you want an even worse one, look at Uwatec's Smart Pro. I have this computer and love it in the basic mode, but when you get into microbubble (MB) suppression you really have to be smart (pun intended). In microbubble suppression mode, the computer will RECOMMEND level stops, but doesn't require them. Further more, the no stop time it shows is only the level (RECOMMENDED) no-stop time, not the deco no-stop time. Confused yet? Since level stops are only recommended, the computer will allow you to ignore them and continue diving, but you'll never know what you're NDL is... I think you see where I'm going. Everytime you ignore a level stop, the computer simply reverts to a less conservative level of MB suppression. NDL is not shown until it reverts all the way back to MB level 0 (no MB suppression), at which time you may have already passed your deepest required deco-stop...

If you understand that recreational scuba (ie. non-decompression diving) is indeed decompression diving with decompression built into the acents and safety stops (ie. no formal stops required). And you furthermore view the level stops as required deco stops or MB level no-stop time as deco no-stop time, the Smart Pro is a great computer. But how many recreational divers, even the savy ones, will remember all of this when cruising a reef in Cozumel.

 

[SeaJay]

If you understand that recreational scuba (ie. non-decompression diving) is indeed decompression diving with decompression built into the acents and safety stops (ie. no formal stops required).

Yeah, what Coz said.

I very seldom need to worry about small deco obligations. They are planned, but I don't use gauge mode on my VyTec

...So how do you plan deco?

...and don't plan to start unless I take a class on helium for which the Suunto's don't have a model.

Nobody I know that dives trimix uses a computer. They are on the market. They are available... Not by Suunto, but by other well-respected electronics suppliers.

Nonetheless, no trimix-certified diver I know uses one. They may use a laptop to plan their dive, but they do not use a computer on the dive. Any theories on why?

I pay minimal attention to NDL's, but especially in warm water I do pay attention to them. I like to get more than one dive in per day and like to account for that residual nitrogen without having to worry about tables and arithmetic (I am great at math, lousy at arithmetic, LOL).

Me too. No need to do any arithmetic.

The other issue is that doing two or three dives per day on one fill of my dual 100's, I will run into gas limitations so I have to break my dive plans into shorter dives and follow that or I won't have enough gas to do more dives. Again, it is difficult in cold water and heavy gear to incur a huge decompression obligation that way.

I gotcha. Off the top of my head, something tells me that an hour surface interval between each dive would be your magic number. Care to put that into your Vyper and tell me what happens? Maybe there's a pattern, so that you don't have to do any arithmetic.

 

[loosebits]

Thanks everyone.

When I'm planning my own dive, I don't have a problem but diving in Coz means going off their profiles which seem a little to liberal for Suuntos. If I do get formal deco training, I will likely use my computer as an expensive bottom time/depth guage but until then I just wanted a better feel for when the Suunto would clear itself before hitting the ceiling and when I would hit the ceiling with time left for the stop.

I do realize that this is just a computer and it isn't actually telling me when I am/am not going to get bent but since I can set my personal comfort limits anywhere I want, I'll just set them at the limits of Suunto's RGBM. It's just to see where those limits are, I need to forecast what the Suunto's going to do (will it clear before I hit the ceiling).

Looks like someone would greatly benefit from instruction in decompression physiology

I do have a fairly good understand of deco theory (at least for someone who hasn't taken decompression diving) but I can't do the calculations the Vyper is doing in my head and without it telling me which compartments in its model are loaded, I have no way of reliably knowing if the deco obligation will clear.

 

[SeaJay]

I do have a fairly good understand of deco theory (at least for someone who hasn't taken decompression diving) but I can't do the calculations the Vyper is doing in my head and without it telling me which compartments in its model are loaded, I have no way of reliably knowing if the deco obligation will clear.

Does it matter?

I mean, does it matter which compartment it is? You aren't going to know which compartment it is until you download the information on your desktop computer anyway. It's not like that's shown "on the fly."

Let me see if I can put this another way: Let's say that you had a computer that showed you 10 minutes longer on your NDL than your Suunto. (It happens.) Which do you believe? Is this simply a matter of believing one computer to be "more conservative" than another?

What happens when it's not consistent? I mean, what if, on your first dive, the Suunto was actually LESS conservative than your other computer? Later, on subsequent dives, it appears to be MORE conservative. Which do you believe? Do you buy a third computer to see which computer is the wrong one? (This is what US Navy Submariners do, by the way.)

...And the bottom line is that none of these will prevent you from getting bent, even if you follow them to the letter. Three computers is an investment of what... $2,000?

Why not instead embrace the idea that all diving is decompression diving, and then learn it from there? That way, no matter what your numbers are, or whether you stayed within NDL or not, you'll know what is going on.