Hey Hoover ~ Did you ruin someone's dive?

[aquamarin]

I was extremely lucky to do my first 20 dives after ow with my super-great big brother, who also happens to be an excellent diver and very impatient teacher. I was a disaster especially on air consumption, but he really cured me I felt guilty and terrible for ending our dives too early, and I am grateful for all the advice he gave me.

Still far from experienced (40 dives in total, 14 months) I went on holiday (Red Sea) alone. First days were great, different boats, different buddies, no problems. Last day my buddy was aow with 20 dives, best gear money can buy (and lots of it). Morning dive he went from 200 to 50 bar (sorry don't know US terms) in 30 minutes - no wonder the way he kept paddling and yo-yoing (rather "funny" when he went through a narrow swim-through, stirring up all the sand in the neighbourhood - even a resident lionfish came out with a look of total surprise / mystery). Had a little current there and we spent quite some time at 25-30 meters. But still...We surfaced (of course) - I still had 140 bar left. Remembering my own first dives, I wanted to give some advice on the bouyancy issue. His response was that no OW could teach him anything. Riiiiight.

Next dive his 15 liter tank kept him going for 40 minutes (max dive time was 60), so at least our dive was a little longer. On the other hand, during the dive he went from 18 meters to surface to 24 meters within approx. 2 minutes. It really scared me, especially when his nose started bleeding. We ended the dive and on the boat I asked what happened. He said, he'd gone to the surface on purpose and went to 24 meters, because he wanted a better dive profile ???

I don't have a problem with hoover-buddies - as long as they want to improve and are realistic about their skills. What I don't like, are loud and over-confident know-it-alls.

Oops, got a little carried away there

 

[FatCat]

SAC means a lot when you're talking about your diving SAC, not your sitting on the surface SAC.

As I said, it's not fixed. I can predict for a given profile, but that's not SAC, that's experience.

The math thing is just balderdash (this is a family forum, right).

 

[jonnythan]

FatCat, are you saying gas planning is irrelevant and impossible without a ton of experience? That there's no use planning your gas if you're a brand new diver?

 

[Uncle Pug]

Knowing your SAC at several different work loads allows you to calculate your gas needs for a dive. You are correct in that your rate of consumption varies but it is possible to have useful approximations for resting, swimming, working, emergency.

 

[boomx5]

SAC means nothing.

Gas consumption is everything when planning a dive, but you should know that being an instructor.

 

[FatCat]

Gas managment is something totally different from calculating SAC-rates. Gas managment is dive planning. And yes, that's very important.

Calculating SAC rates for different workloads is... guesstimating based on... are you ready?... ready??... EXPERIENCE!

You can apply any which formula you want, you'll still need past dive data to work with.

So, a new diver will have to guess, based on the few dives he or she has already done. Don't expect a very accurate estimate though. Which is why a new diver should restrict himself to dives well within the NDL and with the option of a direct ascent until said diver has enough data to work with.

 

[ozarkjim]

SAC means a lot when you're talking about your diving SAC, not your sitting on the surface SAC.

Please tell me what SAC means. I thought it meant surface air consumption. How do you have surface air consumption when you are not at the surface.

 

[ranger979]

My answer to that is to be upfront with your buddy about your concerns. At a minimum, you're setting expectations and establishing good buddy communication before the dive. Sometimes you will find alternative solutions. Always you will be able to relax during the dive without worrying about what your buddy will think.

Sometimes I'll offer to swap tanks with a buddy who's diving a smaller one. And sometimes we just agree beforehand to do an air share for part of the dive ... one of the huge advantages to diving a 7' hose is that you can swim comfortably side-by-side while sharing air. I did this on Sunday with a dive buddy and we extended our dive by 15 minutes.

... Bob (Grateful Diver)

I always have mentioned my concern but in the back of my mind I'm wondering if they're just trying to be nice and patient with a newbie. In practice it really hasn't been much of an issue. Almost all of my dives have been in lake or quarries with a max depth of 30 to 40fsw. We generally just come up after about an hour an very often have 1000 psi or more left.

 

[jonnythan]

Please tell me what SAC means. I thought it meant surface air consumption. How do you have surface air consumption when you are not at the surface.

Pretend it means when you're diving on the surface. The idea is that it's the amount of gas you would use when diving at exactly 1 ATM, not when sitting in your living room at 1 ATM.

 

[FatCat]

Please tell me what SAC means. I thought it meant surface air consumption. How do you have surface air consumption when you are not at the surface.

It does. The brainiacs here are just showing off and forget to mention that they are talking about air consumption relative to surface air consumption. This varies, depending on experience, temperature, viz, workload, physical fitness, etc.