Newb question about weights and bouyancy

[Ashley1989]

Hello, I have a really newbie question that I am curious about.

I have 11 dives, 8 in Thailand and 3 in Cozumel

My question is on most of my dives the instructor starts me off with a certain amount of weight and then once my tank is about 1/2 full I start to become more buoyant so they add 2-4lbs to my pocket...I didn't really think anything of it in Thailand but then when I went to cozumel the divemaster did the same thing I told them I dove with 16lbs in thailand so they gave me 20lbs once I had around 1/2 a tank left they added 4lbs to my pocket, as with an empty BCD I had to fin down a bit to maintain the same depth, so my question is why once we got to the surface did the DM take the weights out then on the second dive pop them back in my pocket half way through the dive, instead of just adding the 4lbs to my belt from the start? I later did a shore dive with a buddy with 24lbs from the start and it worked well for me and had no buoyancy issues. I understand the way to tell if you are properly weighted with breathing in with a 3/4 empty tank and you should be at mask level, but when diving new places I would like to have a good idea as to how much weight to use...Am I missing a skill here and why don't I just start more weighted rather than being too light near the end and adding weight?

Thanks for the long read and any input you have

 

[Divegoose]

Not sure why they would take the extra 4 lbs out, then put them back in half way through the next dive. Were you wearing the same exposure protection in Cozumel that you were wearing in Thailand? Were you using the same size tank? I suspect the divemaster was just making sure you were weighted appropriately through trial and error. Now that you know you require 24 lbs, you should be able to start and end a dive without adding any extra weight.

Dive safe !!

Divegoose

 

[Ashley1989]

3mm shortie in thailand and just a rashguard in cozumel same size tank

 

[Saniflush]

I think most on here will tell you that you probably are using too much weight in general but only you can answer that for sure.
The difference in a rash guard and a 3mm shortie should account for some amount of difference anyway (it is between 2 and 3 pounds of buoyancy for me)
More than likely as you dive more and get more comfortable, you will begin to need less weight.

 

[kmarks]

A tank full of compressed air weighs considerably more than an empty tank, which is why you often start to float towards the end of a dive. You may also be unknowingly changing how much air you are holding in your lungs. Properly weighted, you should never have to "fin down" to sink, but just blow out the air in your lungs and BC. Knowing that you have issues with this, your DMs are adding weight to help you compensate. It works, but it's probably not the best way to solve the "problem." More experience diving, controlling your breathing, understanding your buoyancy, etc., will help.

When you do your weight check, it's with a full tank, not 3/4 empty, a normal breath, an empty BC, and you should be eye level on the water.

 

[Rred]

Sounds like the divemaster said to himself "Sure, but this newb is overweighted" and halfway through the dive, he realize he was wrong so he put the weight back.

 

[guruboy]

You should have all the weight you need for the dive the entire time.

If for some reason you need to thumb the dive, enough weight should be ditch-able that you can still safely swim yourself up.

 

[guruboy]

Sounds like the divemaster said to himself "Sure, but this newb is overweighted" and halfway through the dive, he realize he was wrong so he put the weight back.

Agreed

 

[guruboy]

When you do your weight check, it's with a full tank, not 3/4 empty, a normal breath, an empty BC, and you should be eye level on the water.

That is wrong. You should sink with an empty BC if you have a full tank and are properly weighted,

A weight check is usually done at 500psi, which is the "generally agreed upon" minimum gas you should have when beginning a safety stop.

 

[NorCalDM]

3mm shortie in thailand and just a rashguard in cozumel same size tank

16 lbs with the wetsuit and 20 without? You should have been able to use less weight in Cozumel with no neoprene on.