Comments on: Scuba Diving Computer – Scuba: Dive Computer Algorithms question?

By: Todd W

Todd W — Wed, 14 Jan 2009 23:57:04 +0000

When I was researching buying my computer, I recall that Sunnto was the most conservative at the time, while oceanic tended to give you a little more. I went with the Sunnto. Honestly though, any recreational dive computer is going to give you very safe times compared to what Navy and commercial divers do. They are on the edge, any recreational computer is waaay more conservative.

By: scubabob

scubabob — Tue, 13 Jan 2009 09:25:58 +0000

1/ Yes it’s safe. Even aggressive computers still dive at or within NDL.
2/ They can, yes, but usually it’s the ones with a micro bubble programmable limit that do. Since your fiance is a new diver and you’re following what appears to be a open water cert dive profile most weekends, you aren’t pushing NDL to worry about decos. You’re going to be ******* the tank dry before you hit any deco obligations. It’s almost like worrying about a fire suppression system on your car for a trip to the corner store. You’re not racing, the fuel is relatively stable and you’re not pushing the limits on anything. For your purposes, there’s not going to be any significant difference unless you’re on nitrox and your partner on air.. Even if there was, you should follow the computer with the more conservative profile suggestions anyway. You want to be safe…that’s being safe.

By: ron

ron — Sat, 10 Jan 2009 00:08:46 +0000

A) I’ve forwarded your question to my brother John who owns a Professional Diving Company in Gosport, he is also author of the Professional Divers Handbook.

B) My brother said the answer was relaltively simple, but one of his friends Dr. Martin Sayer, who is the Head of the National Facility for Scientific Diving based in Argyll could give a better one.

C) John,

1. Is it *entirely* safe to rely on 1 brand (along with dive tables of course)?

To a degree the answer is yes, as long as you are confident in that brand. However, it would seem prudent to always use two different computers that use different algorithms (Buhlmann versus RGBM) and always default to the most conservative. In the same way as we have redundant or secondary air sources, I can’t see why a secondary/redundant computer shouldn’t also be standard. No-one reallly understands what algorithms are being used, what they actually mean, and how they perform. So using two different ones would appear a good approach.

In general terms (and things are always changing) SUUNTO and UWATEC are the two brands that appear to dedicate resources and funding into algorithm testing and development. A lot of the other brands buy in the algorithms in a “black box” way – ie, they have no idea as to what the background theory and/or testing may be.

2. Do the decompression stop depth and times etc vary very much between manufacturers?

They vary markedly and a lot of care should be exercised in choosing a computer. In general, and only at the moment, you would appear to be relatively safe with brands such as UWATEC and SUUNTO. However, as you go away from the major brands you are moving away from brands that have a record of funded development and testing. Although there are a number of studies that have examined single dive exposures (see Lippmann in the SPUMS journal in 2005) the main error seems to start appearing with both repetitive diving and multi-day repetitive diving. You can end up with massive differences using some makes and models (see Sayer et al., in SPUMS 2008). There are no hard and fast rules. However, defaulting to the more conservative computer (of renowned and known brand) would seem the basic approach to ensuring safety.

Hope that helps

Martin

________________________________

Dr Martin Sayer FSUT
Head of Unit
NERC National Facility for Scientific Diving
& Dunstaffnage Hyperbaric Unit
Scottish Association for Marine Science
Dunbeg, Oban, Argyll PA37 1QA, UK

Editor, Underwater Technology -