Positively Bouyant Dives

[wes]

Lately I have been diving in the cold Oregon Surf. It gets kind of rough and faster swimming helps alot. I am using the Cressi 2000 HF fins which are great and provide alot of thrust when needed. It felt like I was getting alot of drag from my weight belt so tried without it. Even though I am now maybe 5 lbs positively bouyant because of my wetsuit I still like it much more without the weight belt. It just means I kick a bit harder to get down and then can relax on the way back up. this got me thinking about deeper dives and safety and how it might work well to be positively bouyant the whole time. I read about a constant ballast deep dive Eric Fattah did where his legs cramped or didn;t want to kick due to some lack of oxygen on the way back up. What if we had a wetsuit that would be imcompressible so the bouyancy was constant at depth and set it up so the diver was always bouyant even with collapsed lungs. It seems with the good fins we have now and a more streamlined suit it would be pretty easy to overcome the bouyancy on the way down and then glide back up. I found this link of Naval research on a wetsuit material with microsphere which are mini glass shperes that don't compress so bouyancy is the same at all depths: http://www.stormingmedia.us/35/3526/A352603.html
With a suit made of this material with streamlined mono leg(s) and mono fin and a free ride back up it would seem deeper constant ballast dives would be possible and safer too. Any thoughts or work been done on this? Cheers Wes Lapp

 

[Longfins]

Currently those glass microsphere costs around ~500$ per 1/2 cubic foot if you want to try making some . The polymer microsphere may cost less, but not by much.

There's a reason the military is doing it first!

Peter S.

 

[wes]

Cost of 3M Microspheres for Wetsuit

Peter S.,

It's a very good point that these microspheres may be very expensive. I have since looked into that and on the 3M website they mention the "K20" microspheres as being "low cost" so I chose those to do my analysis with.
http://multimedia.mmm.com/mws/mediawebserver.dyn?OOOOOOxV2&bOhr5OAr5OOO0HuzKnnnnM-
The "K20" microspheres are 0.2 g/cm^3 so about 1/5 the density of water. I checked with a supplier and a 60 lbs box cost $3.80/lbs so about $47.43/cubic foot. To make a wetsuit with 84% microspheres by volume (about the same volume of air in standard neoprene) that provided a lift of 7 kg (this may be way too much lift I am not sure) would be 1.8 kg of microspheres or 3.9 lbs. This would cost about $15 just for the microspheres, not to bad I think. The total wetsuit would way about 3.9kg or 8.6 lbs Do you think that a diver would need or want 7kg or 15 lbs of lift or would this be way to much? Cheers Wes

 

[donmoore]

Very interesting technology. A few points on staying buoyant through the whole dive. Even if you stop the compression of the wetsuit, your lungs and tissue still compress. To try and offset this compression and lost of buoyancy at depth you would have to be extremely buoyant at the surface, which would really waste a lot of energy on the way down. I don’t think it would be practical or beneficial to try and be buoyant the whole dive. Not that the wetsuit technology isn’t fascinating and may prove to be very useful.

In most cases the only time you need positive buoyancy is in the last 12 or so meters. This is where the danger of shallow water blackout exists from the vacuum effect of the lungs drawing the O2 back out of the blood, and the breathold time is longest.

My normal suit is made out of Yamamoto 45 and has a real buoyancy change because it is soft and compresses easy. I have grown to like it because at about 9 meters from the surface on the ascent, it really expands and I feel safe that I will make it to surface regardless what happens. On surface I float high which is nice in choppy conditions.

Some people don’t like a suit that changes buoyancy so much. For them the microspheres, if reasonable priced, might be good, but I suspect the best market for the microsphers would be people who stay down a long-time, like scuba and tech divers.
don

 

[wes]

Bouancy at Depth?

Don Moore,

Wow, excellent perspective on liking the extra bouyancy at the end of the dive just before surfacing. I don't have alot of experience with deep dives though I was thinking of deeper dives when this idea occured to me. I did a 100' plus dive in Kosrae where its very warm with no thermocline so wore just a thin neoprene vest so I would float easier for the breathe up on the surface. It was a bit disturbing as I went negatively bouyant past about 40' and then sunk quite quickly. As I was nearing my deepest point I was having to work very very little almost coasting downward so by the time I turned "pulled up" and turned around it was a shockingly intense amount of effort to get started back to the surface. My wife watching from the surface said she noticed that I was kicking really hard as I turned around and she thought I might have been panicking. Then I slowed down my kicks into a more normal pace as I started to rise and she realized I wasn't panicked. Now I think how nice it would be to work harder on the way down (less hard once the lung bouyancy was lost) and then on the way back up be able to totally relax and enjoy the ride and view back up. With a more streamlined suit I think coming up would be quite speedy as well. Then "recreational" dives to 100 plus feet wouldn't be so hard or potentially dangerous. Cheers Wes

 

[Longfins]

Re: Cost of 3M Microspheres for Wetsuit

Originally posted by wes
Peter S.,

It's a very good point that these microspheres may be very expensive. I have since looked into that and on the 3M website they mention the "K20" microspheres as being "low cost" so I chose those to do my analysis with.
http://multimedia.mmm.com/mws/mediawebserver.dyn?OOOOOOxV2&bOhr5OAr5OOO0HuzKnnnnM-
The "K20" microspheres are 0.2 g/cm^3 so about 1/5 the density of water. I checked with a supplier and a 60 lbs box cost $3.80/lbs so about $47.43/cubic foot. To make a wetsuit with 84% microspheres by volume (about the same volume of air in standard neoprene) that provided a lift of 7 kg (this may be way too much lift I am not sure) would be 1.8 kg of microspheres or 3.9 lbs. This would cost about $15 just for the microspheres, not to bad I think. The total wetsuit would way about 3.9kg or 8.6 lbs Do you think that a diver would need or want 7kg or 15 lbs of lift or would this be way to much? Cheers Wes

Wes,

You're right. I looked into this quite a ways back and I believed I had the deep application spheres quoted (K37, S32, S38, etc) and those are quite expensive. I didn't want 10% of the spheres' performance to disappear by 300-400m because some percentage will disappear at shallower depths.

Several points though:

- You can't pack 84% microsphere by volume into rubber and expect it to hold together. There isn't enough rubber matrix to adhere to the sphere and still have any 'give'. 50% is still optimistic. And even so the rubber (assuming you can find one with a Shore A Hardness number low enough) will require development to adhere to the spheres well and still have good tear strength. If you pack in too much spheres you won't be able to flex the material at all no matter how pliable the rubber is.

- The buoyancy you get from the spheres is less than you think when you start looking at more realistic volume percentages. Syntactic foams made for ROVs in epoxy matrix have densities that are less than seawater but are still hefty chunks of bricks. I believe the 'true density' numbers in the spec. doesn't account for the interstitial volume the spheres occupy.

- If you work the thermal conductivity numbers, you'll find these spheres + rubber are pretty poor insulator compared to foam rubber. So as a consequence you'll need to use a thicker material, which makes the suit less comfortable. And the more rubber you replace (to keep the material flexible) the less insulation you will have. You see what I mean.

Anyway, good on you for looking into all this. As Don also mentioned, you won't really end up with a constant buoyancy anyway, so the development may have less return than the investment depending on who's doing it.

Best,

Peter S.

 

[donmoore]

you won't really end up with a constant buoyancy anyway

Wes and Peter,
You guys are good with the math and science. Just thinking aloud. If a diver has 6-liter lungs, at 99 feet their air volume will be reduced to 2 liters. Is that correct? So that would be a buoyancy loss of 4 liters. Is there even 4 liters of air in a wet suit? I think the buoyancy loss from the compression of the lungs and tissue would be such a large percent of the total loss that you could never get close to constant buoyancy anyway.
Just a thought,
don

 

[wes]

Normal Loss of Lung volume Bouyancy

Don Moore,

You are right that the initial flotation you get starting with 6 liters of air in your lungs soons dwindles to very little at depth. 6 liters of air is about 6.1 kg (13.5) lbs of floatation in seawater. This drops to about 1/3 at 99 feet so would be only 2kg (4.4 lbs) just like you posted. The way it works for me though is a bit different as I am positively bouyant on the surface with a full breath of air and negatively bouyant when I exhale. So the "bouyancy" in my lungs ends up being split 1/2 and 1/2 from being positive and negative. In other words at the surface I'm neutral with about 1/2 a breath full of air so the second 1/2 of the breath full gives me a positive bouyancy (assuming 6 liters total = 6 kg bouyancy) of only 3 kg bouyancy at the surface. Then as I dive at 10 meters (32 feet) the pressure doubles so my 6 liters goes to 3 liters so I loose 3 kg but I started out 3kg bouyant so now I am totally neutral. Then as I go deeper down the bouyancy drops close to zero so then I am 3kg negativley bouyant. If I had a suit that had 5kg of bouyancy at any depth I would be plus 8kg at the surface, plus 5kg at 10meters (32 feet) and plus 2kg at 100meters (320 feet). This is the idea of what I would like to try out. I think it would be a bit of work to start off to get down (one could always dive off a platform to get started like from the deck of a boat) and then easier but still work all the way down. On the way back up the bouyancy would increase and I think probably you would end up putting your hands out to slow yourself down some as you neared the surface.

Cheers Wes

 

[wes]

Would microspheres even work?

Longfins,

Seems like you are right on all points. I was wondering if the neoprene flexs from the air bubbles being able to squish and change shape then would the microspheres be much less flexy. Seems like the answer is yes the mircospheres would make a very stiff neoprene compared to air of nitrogen bubbles. I hadn't thought about the thermal conductivity much, in some ways having it be less thermally insulating might be good if it has to be thicker and then you could dive in quite warm waters and not overheat. You mentioned that getting 84% microspheres by volume is not achievable, you might be right there too, I took 84% as a theoretical calulation from how much air should be in light density neoprene, I have no idea how this would go across to compare with microspheres. Here is a link where the navy did some research into this. Anyone up for trying to get a full copy of this report that appears to be published and public?
cheers Wes
http://www.stormingmedia.us/35/3526/A352603.html

 

[Longfins]

Wes,

The report dates to June 1973. This is really old stuff. The military usually doesn't declassify or publish research that is useful to them unless there are some related or similar information already existing in the public domain.


Peter S.

 

[efattah]

Some comments:

- I have done extensive research on incompressible suits. What you don't realize is that soft silicone rubber has a lower thermal conductivity (better insulation) than collapsed neoprene foam. So, once you get below about 20-30m, solid silicone would be warmer than neoprene foam. I have some of these solid silicone sheets, and sometimes I put them under my suit for extra warmth without extra buoyancy shift

- The deepest dive will always be done by doing the work on the ascent. This is because working on the ascent is 'free', because of the blood shift. At the start of the dive, there is lots of blood in the legs, so kicking burns O2 as fresh blood keeps being pumped into the legs -- not good. At the bottom, the blood shift is so strong (especially in cold water), that there is almost no blood pumping to the legs, so kicking with the legs doesn't drain hardly any O2 from the blood. Instead, it drains the ATP/CrP/myoglobin energy stores, and then the legs start creating lactic acid. That's a good sign, it means you are using 'local' energy stores in the legs.

 

[wes]

Incompressible Silicone Wetsuits

Eric,

Its fascinating that you have thought about this so much and you have experience with using an incompressible insulating system already. Do you think it would work to mix microspheres into a silicone matrix to make a non compressible bouyant wetsuit material? Cheers Wes

 

[wes]

Deepest Dive with work on Ascent

Eric,

That's an excellent point about using annerobic (non oxygen based) metabolisim on the ascent phase of the dive as being free. It does though, seem like I remember a dive you recounted, where you experienced significant difficulty getting your legs to function to bring you back up to the surface. Do you think having positive bouyancy in that situration would be a good thing or "safer" in general. I guess I am approaching this from an optimization standpoint where I see the work done in swimming down and up largley wasted as the hydrodynamic drag is so huge for the typical free diver versus what could be achieved. It would seem a reduction of drag of 3 to 4 times could be achieved (more like a fish). In this low drag scenario then, the work of swimming 600 feet round trip to a 300 foot depth dive would much less dominate the use of oxygen. In this case balancing or minimizing the positive and negative bouyancy would become key to reduce the effort of the dive. This is where an incompressible wetsuit could help minimize the oxygen load of the swimming effort.

 

[cdavis]

Interesting and different thread.

Don, the math isn't quite right, 6 liters at the surface becomes 1.5 liters at 99 ft (3 atm of water plus 1 atm of atmosphere)

Connor

 

[efattah]

Back in 2001 when I had the extreme leg fatigue, I was actually doing everything right in terms of dive profile (most of the work being done on the ascent). The problem was that I was training incorrectly, so I had very poor stores of energy in my legs. As a result, my legs would fail as little as seven kicks off the bottom; that shows how 'blood shifted' my legs were. Now, with different training, I sprint to the surface under the same conditions, with only minor leg fatigue. Also, using a slightly softer monofin helps.

I already thought of using microspheres in a silicone matrix. Maybe a project I'll take on after the new depth computer.

 

[derelictp]

There is a limit though...

..to how heavy weighted I can be and still gain.

I agree that the effort should be made on the ascent but I have found that to much weight will OFFCOURSE make the dive harder. The problem is finding the perfect amount of weight.
I would like to have smaller weights, maybe as small as 0,1 kg to get the amount excactly right.

I have noticed that on my dives the weight makes a big difference, 2kg is to little but 2,5kg is to much for dives deeper than 60m in the lake where I dive. I guess 2,2-2,3kg should be perfect for me. It seems that the weights is more important to get excactly right in a lake compared to saltwater where it does not seems to make much difference...

I have noticed also that dives in saltwater is much more physical demanding than in saltwater, my ascent speeds are 8-15% faster than in the lake at the same depth and the dive seems a lot easier. I can't explain it though, the water density is 2,5-3% higher in saltwater but it seems like a tiny difference to make a big difference in the dives....

 

[wes]

Leg Fatigue and Microshpere Silicone

Eric,

Thanks for the posts and feedback. Sharing your experience is awesome and so much nicer than theory. Also I very much admire the work you have done on the fluid goggles. Cheers Wes Lapp