Neutral at surface or 10 feet?

[MHK]

At the beginning of my dive I'm anywhere from 4 - 8 lbs heavier than at the end, depending on the cylinder(s) I'm using. So, that's extra weight to help start the dive. At depth, I'll be heavy throughout the dive anyway and will simply compensate with the wing, so that's not an issue. At the end of the dive, I'll be properly weighted for my deco/safety stop at 10'. Proper horizontal positioning allows a quick kick that will help if I rise a bit. This kicking should only be used if necessary, but if I use proper weighting and bouyancy control technique in the first place, this would be the best way to avoid needing to kick at all. The ascent to the surface after the 10' stop is almost a moot point because even though I may be a bit bouyant as I ascend from the 10' stop, 10' is probably not enough distance to turn me into a Polaris missle. This method of establishing how much weight I need should yield the least amount of weight I can get away with. In addition to that, if I were to have a wing failure at depth while wearing a wetsuit, I would have the easiest time swimming up my rig, since I'm using the least amount of weight possible.

You're on the correct track, but a few minor points I would offer. When you say that "you'll be heavy throughout the dive so that's not an issue" I want to point out specifically, that the minor weight added by virtue of air in the tanks isn't a serious concern, and as you suggest you can compensate for that with your BC. However, it's important to note that diving extremely overweighted and then trying to comepnsate via a BCD, may potentially be a problem for several notable reasons. 1) you create dynamically instable air sources that throw off your balance and trim. 2) By working harder you are increasing the susceptibility to C02 retention.

I also wanted to address the notion that going from 10' to the surface isn't of concern. When properly weighted, ie; holding your stop at 10', getting to the surface then becomes more about breath control then the need to inflate your BC and/or rocketing up from 10'. We like to do slow ascents, even in the last 10'..

Michael, I don't want to impose, but I hope you will allow me to ask you one more question. Does the new DIR video series include a more in depth view of the DIR philosophy as an extension of the book or is it intended to accomplish a completely different purpose than the book?

The video is more along the lines of JJ and George explaining much of the WHY's behind the system as well as explaining how they worked through the trials and tribulations that got DIR where it is today. It's an interesting historical outlook from two of the true pioneers. The book speaks, I believe, more to the HOW's of the system. SO in many respects, I suspect the DVD's compliment the book.

Hope that helps

Michael Kane

 

[headhunter]

You're on the correct track, but a few minor points I would offer. When you say that "you'll be heavy throughout the dive so that's not an issue" I want to point out specifically, that the minor weight added by virtue of air in the tanks isn't a serious concern, and as you suggest you can compensate for that with your BC. However, it's important to note that diving extremely overweighted and then trying to comepnsate via a BCD, may potentially be a problem for several notable reasons. 1) you create dynamically instable air sources that throw off your balance and trim. 2) By working harder you are increasing the susceptibility to C02 retention.

I also wanted to address th enotion that going from 10' to the surface isn't of concern. When properly weighted, ie; holding your stop at 10', getting to the surface then becomes more about breath control then the need to inflate your BC and/or rocketing up from 10'. We like to do slow ascents, even in the last 10'..



The video is more along the lines of JJ and George explaining much of the WHY's behind the system as well as explaining how they worked through the trials and tribulations that got DIR where it is today. It's an interesting historical outlook from two of the true pioneers. The book speaks, I believe, more to the HOW's of the system. SO in many respects, I suspect the DVD's compliment the book.

Hope that helps

Michael Kane

Thanks for the added points. That's actually what I was thinking. I wasn't advocatiing the notion of "overweighting". My word picture of rocketing to the surface from 10' came from an almost cartoonish mental image of the wetsuit expanding, but I realize that it doesn't actually expand that much.

The DVD sounds like it's right up my alley, so I'll have to order a copy. It sounds like something that I might be able to show a friend who would ask me what DIR is. I've got a couple of friends in mind that have never heard of DIR. I didn't want to mention it to them until I had a more thorough understanding of it. They are people who have not been diving for a while and lately I've been getting them excited about starting up again.

Again, I appreciate your time and patience.

Thank you.

Christian

 

[jckusa]

I recently signed up with scubaboard.com and have been doing a bunch of reading. This is my first post.

I too am signed up for an upcoming DIR-F class (August/Gilboa). I'm trying to do as much "homework" as possible, like headhunter, to get the most out of the class.

I read this thread with interest, as I've recently been working on this issue. One post said that 6lbs to compensate for the gas is 6lbs too much, and another said that the gas weight is not significant. Breath control was indicated as the "answer" in both posts. A quick study of lung capacity tells me that a normal, average breath will change my buoyancy by about 1 pound. An average, deepest-breath-I-can-possibly-take, will change my buoyancy by about 9 lbs.

My question is this. Shouldn't my buoyancy goal to be centered in this breath control range? ie. With "centered" breathing, I sink at the start of my dive, using my BC to compensate for the weight of the gas in my tank. At the end of my dive, with "centered" breathing, I am neutrally buoyant at 10' with 500psi in my tank and a fully vented BC and drysuit. This way, with breathing "off the top", or breathing "off the bottom", I can ascend or descend, respectively.

John

 

[PatH]

I read this thread with interest, as I've recently been working on this issue. One post said that 6lbs to compensate for the gas is 6lbs too much, and another said that the gas weight is not significant. Breath control was indicated as the "answer" in both posts. A quick study of lung capacity tells me that a normal, average breath will change my buoyancy by about 1 pound. An average, deepest-breath-I-can-possibly-take, will change my buoyancy by about 9 lbs.

My question is this. Shouldn't my buoyancy goal to be centered in this breath control range? ie. With "centered" breathing, I sink at the start of my dive, using my BC to compensate for the weight of the gas in my tank. At the end of my dive, with "centered" breathing, I am neutrally buoyant at 10' with 500psi in my tank and a fully vented BC and drysuit. This way, with breathing "off the top", or breathing "off the bottom", I can ascend or descend, respectively.

John

You have to read the posts specifically for what bouyancy test is being done (floating at eye level, or being neutral in water), when (beginning or end of the dive), and where (surface or at last stop).

The two combinations that seem to line up are:

1) on surface, beginning of dive (full tank), and floating at eye level with empty BC. and
2) at last stop (10'), end of dive (500 psi) and neutral with empty BC.

These two combinations tend to get result in the same weighting with the former being an "indicator" to achieve the latter, which is the acid test.

Breath control is critical to getting them to work as intended. An inexperienced diver will often need to pack on a couple of extra pounds after his surface test because he will find it very difficult to leave the surface as he lacks breath control and comfort. Also, if you get it right, your breat control will bring you slowly back to the sufrace from your last stop. The weight of the compressed air is "accounted" for in the above tests because they don't occur in the same manner/location. Nor will it work if you are wearing large tanks (>80 cf). If you are using large (or double) tanks you will find that the initial guesstimate (at the surface) would leave you light at the final stop. In this case you need to adjust your weighting to ahieve neuatrality at the final stop which is the condition where you can measure for minimum weight needed.

Hope this helps.

 

[jckusa]

You have to read the posts specifically for what bouyancy test is being done (floating at eye level, or being neutral in water), when (beginning or end of the dive), and where (surface or at last stop).

The two combinations that seem to line up are:

1) on surface, beginning of dive (full tank), and floating at eye level with empty BC. and
2) at last stop (10'), end of dive (500 psi) and neutral with empty BC.

These two combinations tend to get result in the same weighting with the former being an "indicator" to achieve the latter, which is the acid test.

I did read the posts specifically and yours seems to differ from others. That was part of the reason for my post, as I'm hearing two different things.

Are you diving wet or dry? Could that be the difference, the loss of buoyancy due to wetsuit compression after the initial descent?

What I'm hearing you say for combination 1 is, once you descent, you could drop six pounds of lead and have no problem staying down at that point in time. That is the same situation you will be in at the end of your dive after consuming most of your gas.

 

[Dan Gibson]

John,

If you come out diving with us, we can work on this prior to the class. I can even break out the fish scale

Dan

I did read the posts specifically and yours seems to differ from others. That was part of the reason for my post, as I'm hearing two different things.

Are you diving wet or dry? Could that be the difference, the loss of buoyancy due to wetsuit compression after the initial descent?

What I'm hearing you say for combination 1 is, once you descent, you could drop six pounds of lead and have no problem staying down at that point in time. That is the same situation you will be in at the end of your dive after consuming most of your gas.

 

[jckusa]

John,

If you come out diving with us, we can work on this prior to the class. I can even break out the fish scale

Dan

That would be great. Just heard back that my regs are ready so I can dive this weekend. I was looking at doing my nitrox checkout dives on Saturday, but can reschedule if needed.

Thanks

 

[PatH]

I did read the posts specifically and yours seems to differ from others. That was part of the reason for my post, as I'm hearing two different things.

Hmm... either something is being poorly understood or I'm really explaining this badly as everything I'm saying should be lining up with what MHK was saying.

Are you diving wet or dry? Could that be the difference, the loss of buoyancy due to wetsuit compression after the initial descent?

I'm referring to a typical single tank (AL80)/wet suit config.

What I'm hearing you say for combination 1 is, once you descent, you could drop six pounds of lead and have no problem staying down at that point in time. That is the same situation you will be in at the end of your dive after consuming most of your gas.

Although I'm not advocating that you actually remove any weight during a dive the reality check is... at depth... yes you probably could drop a pile of weight and stay down easily. However, you would have to put it back on again before ascending. The amount would depend on the type of suit and depth.

Here's the crux of it.

Properly weighted you should be: neutral at your final stop (10'), with about 500 psi in your tanks, with no air in your wing. This is true no matter what configuration of tanks and suits you are diving.

As a guestimate of the desired goal: IF you are a single tank (AL80) , wet suit diver this can be estimated at the start of the dive by: floating in the water with reasonably full lungs, full tank, no air in the BC (don't fin!!). You should float with your eyes just about at the surface... when you breath out: you will sink.

The guesstimate doesn't matter as long as the final product (end of the dive) is correct.

Hope this clarifies any misconceptions I may have caused.

Pat

 

[jckusa]

Thanks Pat,

Think I understand better now. Some of my preconceived ingorance my have had something to do with my misunderstanding.

So, the AL80/wetsuit, full tank, empty BC, eyes at water level, sink when you exhale, is a good rule of thumb that will get you close to what you will need to stay at 10' with 500psi.

What is the recommended method for setting buoyancy, diving dry with various tank sizes/configurations?

This weekend should be a learning experience and can't wait to take the class.

 

[gcbryan]

Take any tank with 500psi and whatever weight will allow you to sink while exhaling and this will work just fine regardless of your tank/suit combination.