Sawtooth Dive Patterns

[FPDocMatt]

I thought a sawtooth dive pattern involved more drastic depth changes, but according to Deco For Divers, you can get a dangerous sawtooth pattern by just going up and down from the upper to the lower parts of a wreck, or going up and down along a reef wall.

Do you more experienced divers make a conscious effort to avoid even small successive ascents and descents during a dive?

 

[TSandM]

I don't think Mark was talking about the rises and falls you do going over coral heads, or over a railing on a ship to the deck beyond. But for example, the wrecks in Nanaimo have a vertical relief of 50 feet or more from the sand to the superstructure; you could go up and down on those wrecks enough to cause yourself some issues. Walls, obviously, would permit even more excursions.

However, those of us who dive caves deal with sawtooth profiles all the time. You simply can't insist that a cave maintain a steady depth, or even that it consistently descend on the way in. I have dived a cave where you go down to 30 for a while, and come up to about 3', before descending to 30 again -- of course, you have to do the whole thing in reverse on exit. Brian Kakuk has written about caves which go from 100 feet to 150, and back up to 100, and back down to 150 -- you either cope with the sawtoothing, or you don't dive the cave.

What we all have to realize is that sawtoothing is not desirable, and if you do it, you have to recognize the parts of your profile which are effectively decompressing the prior segment of the dive, and treat them accordingly.

 

[DevonDiver]

Do you more experienced divers make a conscious effort to avoid even small successive ascents and descents during a dive?

Yes, where possible.

As with caves, wreck penetration dives are often dictated by a pre-determined 'route' through a structure. External (non-penetration) dives do not have those limitations.

When I have to 'saw-tooth' on a dive, I will compensate by ensuring extra conservatism on the ascent... making sure my ascent speed is nice and slow... plus extending safety or deco (as applicable) stops where possible.

 

[Thalassamania]

My first exposure to the problem was at the hands of Carl Edmonds. He presented a paper at the AAUS Dive Computer Workshop that showed an extreme set of saw tooth dives, that were permissible according to the EDGE dive computer, when done with actual human subjects resulted in bends cases. Ralph Osterhout (TEKNA, FARALLON, etc.) exclaimed, "But what kind of booger-eating moron would ever dive a profile like that? To which Parker Turner drawled, "We cave divers to it all the time." Uproarious laughter followed. The paper is in the proceedings on RUBICON.

 

[lionfish-eater]

Yes, on non penetration wreck dives, if we are going to the sand to look for critters, or to look at the prop, we do it at the beginning of a multilevel dive and end the dive viewing shallower parts of the wreck. On reef drift dives, we often follow the contour of the reef, or duck down behind the coral, so the profile can be more sawtooth, but still within a relatively narrow depth range. Other SB'ers, more knowledgeable than I am, can give a more precise definition of the range of variation in depth over time that would need to be exceeded. Additionally, +/- 10 feet has less impact at 100FSW than the same variability at 30FSW, I think.{others feel free to correct, as I don't want to give false info. Please excuse me as I have PADI training from a LDS}