Why no weights?

Question
QUESTION: Hi Mike.  I took my first lesson last night and am thrilled from the experience.  I have good instructors and that makes a world of difference learning in an envirnment such as this.  When I got suited up they said I should try about 10 pounds on my belt.  I am 5'8" and about 185lbs.  I enter the swimming pool with my bc inflated and I'm barely floating(in shallow water) so my instructor told me to egress one weight and that would bring me to about 7lbs.  I had started to release air from my bc to get my weights right and started sinking immediately.  He then told me to take the belt off and to his surprise I did not need the belt at all.  We checked the integrated bc pockets but nothing there.  This is my first experience and wanted to know what would make me sink so easily.  I know that muscle weighs more than fat but I'm not thin.  My instructor was looking at me funny and kinda chuckling the rest of the night which made me laugh too.  We had a ball.  I'm glad I won't have to carry a weight belt.  I'm also thinking that once I get into salt water I will definitely need one.  Thank you.  Tom.

ANSWER: Hi Tom

Wow...it must be nice to not need any weights!!  Your information regarding the relative buoyancy of fat versus muscle is correct and that's the reason you don't need any extra weight for your pool sessions.  I suspect that you're a young and physically fit guy so your body fat is relatively low.  Buoyancy, as you learned in class, is determined by how much you weigh, compared to the weight of an equal volume of water.  If you weigh less, then you float.  Since salt water has salt in it, (wow!!) this salt adds weight to the water.  This extra weight means that something that was neutral (weighs the same thing) in fresh water will now float in salt water since it now weights a little less than an equal volume of salt water.  That can be a bit confusing but I think you get the idea.  So...you are also correct in that you'll probably need some extra weight to sink in salt water.  Also keep in mind that some of your gear, like wetsuits, boots and even the air in your mask will have some buoyant tendencies so you'll need to add weight to sink them. Your BC may also be buoyant since it usually has some residual air trapped in it and, of course, air floats.  Air trapped in your wetsuit will also add buoyancy so take care to let all this air escape as you descend under the water.  

One interesting thing to consider is what happens to all this air as you go deeper in the water.  The pressure will compress it so the volume of the air is less and so is it's buoyancy.  You may actually have to add a little air to your BC in deeper water to compensate for this. Of course, the reverse is also true...you'll have to vent the extra air as you come up because the remaining air will re-expand and add buoyancy.

So, Tom, consider yourself fortunate to be able to sink without extra weights.  Most of us would give our right arm to be able to do that!!

Enjoy your scuba course and Happy Diving!!

Mike Giles
Mike's Dive Center
mikescuba.com

---------- FOLLOW-UP ----------

QUESTION: To answer your question of how old I am...38.  I don't workout as much as I used to so a good 1 inch layer of fat.

Last night I had my second pool session.  This time I didn't have the wrap around bc which made my experience even more comfortable.  I am looking at purchasing my own regs and safe second along with a bc.  Last night I tried the Z2(can't remember the make)with the added swivel on the secondary.  Wow, what a difference in comfort.  The safe second was integrated with my bc inflator, avoiding an extra hose.  I liked that idea.  I'm not sure what I'm going to do about a computer though.  The one I had was too small to read.  Even though I have 20/20 in both eyes I want something that I can read with a glance vs putting it against my mask.  Can you give me some advice on the stuff I'm looking at?  I was told a good safe second is an SS1(again not sure make).  I understand that every product produced is going to do what it's certified to do but...I want something that has a good track record.  It's my life support.  Thanks again Mike!

Tom

Answer
Hey Tom

With regards to your statement about your "1 inch layer of fat", I can only say that physics doesn't lie.  The principles regarding density that I mentioned in my previous reply will apply so you probably have less body fat than you think you do.  In any event...ENJOY the advantage!!

Now I'll address your equipment concerns.  I tend to stay away from specific brand endorsements because I'll get a flood of comments from other brand-loyal readers.  However, almost all of the major brands will have similar equipment and, if you stay with major brands, you shouldn't have any problems with reliability or performance.  There will be slight differences between brands but most of them are not significant.  If you're curious about what I'm carrying in my dive shop, you can check out my website.  It's shown at the end of this response.

I like a back inflating BC. That's different from the "wrap around"  BC you used in your first session and may be what you used in your second session.  In a back inflating BC, all the air goes into a bladder on the back of the BC.  This prevents the squeezing effect of the jacket style and is more comfortable to wear.  Successful use of the back inflating BC requires that you are properly weighted because overweighting will tend to force you into a face down position, especially while on the surface.  I also like the integrated safe second since, as you pointed out, it eliminates an extra hose.  It requires a slightly different method of sharing air since the safe second hose is very short and it can't be passed to another diver.  In reality, you'll probably never need to use your safe second in an actual emergency so combining it with the BC inflator makes even more sense.

Swivels on your regulator can, as you've experienced, make using the regulator much more comfortable.  I have swivels on all of my regulators.  Another item which will make using your primary regulator much more comfortable is a custom molded mouthpiece.  They eliminate all the need to clinch your jaws to keep the regulator in place.  You will probably not be able to get one on your training regulator but we provide lots of them to divers with their own equipment.

 Another item to consider in the selection of a regulator is whether the first stage is a piston type or diaphragm type.  There is no difference in performance but there can be a difference in maintenance.  Piston regulators have a spring chamber which can accumulate sand, silt and, if in very cold water, ice.  It can be hard to rinse this chamber effectively so accumulations of debris can encourage corrosion if not serviced regularly.  Diaphragm regulators do not have this problem since they're sealed.  The next time you're in a dive shop, ask someone to show you the spring chamber in a piston first stage and you'll see what I mean.  You'll only have small slots to use to rinse the chamber.

Now for the computer.  There are lots of choices and I can write pages on how to select and the advantages of each.  Get a Nitrox compatible computer.  They are becoming much more "mainstream" and the price isn't much higher than an air computer.  It will permit you to dive air but will also give you the option to use it for Nitrox diving as well.  You will learn a little about Nitrox in your dive course so I won't go into it here.

Another choice is whether to get an air-integrated computer or not.  Air-integration will allow the computer to sense the air pressure in your tank and it will do several calculations for you.  For example, it will alert you when your air pressure is getting low and it will also compute the number of minutes of air you have remaining in your tank at any time.  If you're getting an air-integrated computer, you now have the choice of whether to have it connected to your tank using a hose (just like the air pressure gauge you have now) or having a hoseless connection where a little transmitter is attached to the first-stage and sends the air pressure information to the computer attached to your wrist.  Obviously, this will allow you to eliminate another hose.

Computers come in different sizes.  The smaller ones tend to be more expensive than the larger ones.  With your 20/20 vision, you shouldn't have any problem reading any of them but if you feel like you need a larger readout, by all means, look for one.  Some readouts are so cluttered that you may have problems picking out what you need so look for a computer that doesn't try to cram everything on one screen.  You can page through different screens, depending on the computer.

You can get magnifying covers to put on the face of your computer and you can also get magnifying lenses (like reading glasses) to put inside your dive mask.

Tom, as you can see, this can get to be a bit complicated so I'd suggest giving it all some thought, check to see what's available and ask lots of questions!!  Don't feel like you have to settle for whatever the local dive shop has to offer.  Dealing with a local dive shop certainly has it's advantages.  Among those is a quick access to a dealer if you have problems.  However, there may be other dive shops within a short drive from your home so don't be afraid to to some shopping.  Good dive gear which is properly maintained, is very reliable so you shouldn't have to worry too much about having a dealer just around the corner.

Tom, if you want information on specific brands, you can get lots of it from the gear testing articles found in Scuba Diving Magazine.  Keep in mind that some of this may be influenced by manufacturer advertising in the magazine but it will give you some idea of what's available and how it's tested.  I can also give you some specific recommendations if you'll contact me through my website.  I just don't think it's ethical to push a specific brand through this advice column.

It sounds like you're having a ball in your training and I wish you only the best in your diving adventures!!

Sincerely,
Mike Giles
Mike's Dive Center
mikescuba.com