DIR-F Report - Sault Ste. Marie CANADA

[Dan MacKay]

Butch103 once bubbled...
...thanks for your input, but I get the part of keeping horizontal...only makes sense, but I will impress again the question snorkle wobbles yes...slates dangle yes....but how much does it affect under water when you are swimming in a slow leisurely manner.

Folks understand I am not a brand new diver, but also not a seasoned veteran.

I guess I will never get what is the quantatative measurement out there that says hey by getting rid of the wobbling snorkle you can get another breath of air under water because you saved that much energy.

I suppose the collective savings as opposed to the individual savings is really the answer.......ut:

Hi all,

Thanks Bob for the explaination of what is happening why drag is a drag for Butch.

When I tossed the trim question I wanted folks to put their thinking caps on and even left a couple of hints along the way to facititate a more complete discussion on the effects of drag.

Aerodynamics and hydrodynamics are very similiar. So if we take take an object and move it through water (say a diver) and play with trim set at various angles we will see much the same thing that happens to an airplane (or submarine for that matter).

Now for a little more brain teasing and a little more of a challenge. As in the air if we increase drag (slightly heads up attitude) we must have a lift component as well. In order to generate lift and drag we must have a motive power as supplied by our fins. As with any wing if we increase the angle of attack we wil eventually stall and must rely on kicking in the verticle position to stay in place or working extremely hard to swim at a 45 degree angle to the the water column. (Anyone ever see anyone doing this before?) Working against a current this is pretty near impossible.

So here are the questions:
1. If my trim is not great and I am heads up explain how lift, drag and propulsion are keeping me at the same place in the water column.

2. If I change nothing and am swimming along as trimmed above and simply stop kicking and freeze, what will happen?

As for ankle weights...I do have a bit of a rave. If you are wearing a wetsuit put the ballast where it belongs, at the center point of your center of gravity or as close to it as possible.

The most common excuse I hear for ankle weights on dry suits is "I trap air in my feet". Get you boots changed for ones that fit. This is an essential part of any well fitting drysuit. Put ballast where it belongs on your weight belt.

 

[ScubaScott]

Dan - a few days after class the group of us got into a pretty good discussion about ankle weights - I've never worn them, as comparred to my bud who claims he can't dive without them. An arguement came up as to what the difference is wearing ankle weights, as compared to fins (rubber type) that are 2#'s negative? I didn't have answer for this one.....

SS

 

[JimC]

1. If my trim is not great and I am heads up explain how lift, drag and propulsion are keeping me at the same place in the water column.

The attached picture, diver a shows the force vectors which would be in effect for a diver swimming in a heads up position. Picture B shows the same forces on someone horizontal.

In order to remain at the same depth the diver must have enough extra weight to counteract the upwards components of the drag and finning forces. Fortunatly for most wetsuit divers, the effective over weighting required is less, as the boyant force of there wetsuit lessens as they decend.

2. If I change nothing and am swimming along as trimmed above and simply stop kicking and freeze, what will happen?

Sink like a rock. While the finning and drag vectors disapear, the upward compoents of these forces also disapear. This throws there boyant vs gravity forces out of sync.

 

[MXGratefulDiver]

ScubaScott once bubbled...
Dan - a few days after class the group of us got into a pretty good discussion about ankle weights - I've never worn them, as comparred to my bud who claims he can't dive without them. An arguement came up as to what the difference is wearing ankle weights, as compared to fins (rubber type) that are 2#'s negative? I didn't have answer for this one.....

SS

I, too, would like a logical answer to the question.

I'd also like to examine the drysuit boots scenario a bit more. I've done a bit of investigating back when I had to replace my drysuit boots ... and they seem to come in "standard" sizes (regardless of who makes them). Although a well-fit boot is as desireable as a well-fit suit, nobody seems to offer a boot that's customized to a particular foot shape. So it isn't as easy to get well-fit boots as it is to get a suit that's customized to fit the rest of your body. Also, drysuit boots seem to be built (as a rule) to accommodate the lowest common denominator ... wide feet. That's why divers switching from a wetsuit to a drysuit often end up having to purchase new fins as well. The end result is that for most people, there's a lot of air space in their boots ... even when they've purchased a well-fit, customized suit. I think this is why ankle weights became so popular. But that's just treating a symptom ... and not in a very efficient manner. There are other alternatives. I know a lot of people who just wear extra socks ... but that still traps air and adds bulk ... furthermore, it reduces the efficiency of your fin stroke as the socks absorb a lot of the motion when you move your feet. Fin keepers restrict the air space in your boots without the need to add weight .... they're a cheap alternative to ankle weights that don't add unneeded weight to your lower body. Gaitors will restrict the movement of air from your legs to your feet ... they're especially effective for the "bag" suit diver to keep air from migrating to the lower legs and feet when you want to invert. Some, like Halcyon and Dive Rite, offer a buckleless gaitor that's really nice if you're diving in kelp or other conditions where snag hazards are a concern. DUI and Seasoft have a different solution ... putting socks on the suit instead of boots and using rock boots or wetsuit boots over those. All of these offer viable alternatives to ankle weights. Depending on the diver, suit, and choice of fins, some of these alternatives will be more effective than others.

Does anyone know of any other solutions to this problem? Or perhaps has heard of a suit manufacturer who offers boots customized to fit as well as the rest of the suit?

... Bob (Grateful Diver)

 

[Dan MacKay]

JimC once bubbled...


The attached picture, diver a shows the force vectors which would be in effect for a diver swimming in a heads up position. Picture B shows the same forces on someone horizontal.

In order to remain at the same depth the diver must have enough extra weight to counteract the upwards components of the drag and finning forces. Fortunatly for most wetsuit divers, the effective over weighting required is less, as the boyant force of there wetsuit lessens as they decend.



Sink like a rock. While the finning and drag vectors disapear, the upward compoents of these forces also disapear. This throws there boyant vs gravity forces out of sync.

Hi Jim,

Good answer but not quite right. If you look at the your diagram the forces are right but unlike an aircraft we have an unique ability as divers. We can hover motionless if we are properly weighted and trimmed out. We should endeavour to behave like lighter than airships that don't require power to hover rather than airplanes which require power just to remain aloft.

The main problem with the out of trim diver is that they actually have a little less air in the BC (Less buoyant not more weight) to counter act the lift component. And as you surmize they will sink like a stone when power is removed. If anyone has ever wondered why they sink when they stop swimming, being out of trim and overwieghting is likely the culprit. The obvious conclusion to be drawn from this is that there is no way in heck that these folks can stop moving. To stop is to sink = more air consumption = increased risk of CO2 buildup = more silt = less bottom time = greater task loading = did I mention more silt etc...everything that is bad in diving. All because of short comings in the most absolutely fundamental priniciple in diving - bouancy and trim.

 

[Dan MacKay]

NWGratefulDiver once bubbled...


I, too, would like a logical answer to the question.

... Bob (Grateful Diver)

Hi Bob,

The logical answer points to a situation that has existed in the sport ever since Jacque himself strapped on his first aqualung.

What I refer to is the pechant in the diving world to substitue equipment for skill. If your suit and boots fit properly in the first place this is no an issue. Typically when someone purchases his/her first and normally ill fitting suit they come back in to the store and report that they are foot light because they do not know any better that in fact the boots/legs are not cut right. The LDS promptly has the right answer and the new diver walks out of the store with a spanky new set(s) of ankle weights. The problem has not been solved merely painted over. They become an immediate crutch and often persist throughout the divers career even after they have purchased suits that fit. At this point they are used out of habit not of need. I have seen divers use one, two and ever three sets of ankle weights. Go figure. I guess they figure more is better.

The solution is not to substitute an additional piece of gear for skill. If you are foot light it likely means:

1. That your whole rig is unbalanced;

2. You have too much air in your suit;

3. You boots are too big and/or your suit is not cut right.

The usual culprit is a combination of all three. Every drysuit manufacturer (that I know of) has boot kits that stores can purchase for a reasonable price which allow you to try them on before you order. A word of advice. Wear the socks you intend to use with the suit and pick the smallest size possible. Remember that they are going to bellow a little when you get in the water.

 

[TCDiver1]

Dan MacKay once bubbled...


Hi Jim,

Good answer but not quite right. If you look at the your diagram the forces are right but unlike an aircraft we have an unique ability as divers. We can hover motionless if we are properly weighted and trimmed out.

Are you forgetting about the Harrier or Osprey Dan?:tease:

Seriously, i like your explanation but would add one last variable.
IMO we don't ever really hover "truely" motionless due the variability of our lung volume. Normal adult, non-working lung tidal volume is the range of 0.5 to 1 litre, therefore, most of us get approx. 2 to 3 lb swing in buoyant effect from breathing underwater.

I'm not arguing with the trim goals you are presenting but rather pointing out why most experienced divers can hover in any position, even if slightly overweighted or out of trim.
Jon

 

[MXGratefulDiver]

Dan MacKay once bubbled...

Every drysuit manufacturer (that I know of) has boot kits that stores can purchase for a reasonable price which allow you to try them on before you order. A word of advice. Wear the socks you intend to use with the suit and pick the smallest size possible. Remember that they are going to bellow a little when you get in the water.

Yes, but this points back to my previous post ... those boot kits are "standardized" so as to fit the widest possible range of feet, therefore there may not be a "good fit" option for a particular diver.

As an example ... when I purchased my suit I did try on the boot kits to see what size boot went on the suit. My options were to get a size 9 (which was the correct length but too tight in the width) or a size 10 (which was the correct width but left about 3/4" of empty space in the toe).

My wife has the opposite problem ... very narrow feet. For her there was only one option, which was to get the boot that was the correct length and figure out how to fill up all that extra air space around her foot.

Drysuit boots aren't like hiking boots or ski boots ... where different manufacturers target a variety of foot shapes for optimum fit, and you have the ability to shop around for the one that fits your foot the best. In other words, you don't have the option to put a Mobby's boot on a Brooks suit (at least not under most normal circumstances, and never without considerable additional expense).

This, more than anything, is what I believe leads to the reliance on the assortment of "crutches" out there to resolve the symptom (floaty feet).

Good technique can teach you how to manage the problem ... but not how to eliminate it.

... Bob (Grateful Diver)

 

[cornfed]

gedunk once bubbled...

Are you forgetting about the Harrier or Osprey Dan?:tease:

What he said applies to those guys as well...

 

[Knavey]

Ok,

Not a DIR diver, but the debates that I have read on the boards have picqued my interest a bit. I personally find all the debate a bit amusing, but I do understand the philosophy behind DIR.

Now a question...

I just finished watching all of the DIR videos on one of the websites...

This one though caught my eye more than others. In basic OW scuba, you are taught to approach the surface with your arm extended and looking to ensure that you don't surface under a boat.

In this VIDEO , NEITHER diver EVER looks up! Is that a standard DIR technique or just oversight?

Again, not a critisism, as I have rather enjoyed the interesting debates and the MANY tips and pointers that I have found in them.