Which is heavier? 1lb of lead or 1lb of feathers?

[trailblazer1229]

Ok, It may seem like a strange question, and I risk sounding like an idiot. But am I really this stupid???

My wife and I conducted a boat dive in salt water a couple of weeks ago. Buoyancy checks revealed her to need 12lbs of lead and I needed 15lbs. We had a great dive to about 40 feet and we were beautifully neutrally bouyant. We used the lead and weight belts from a LDS sponsoring the dive.

The next day we conducted a shore dive to about 14 feet. We had the exact same equipment as the day before. Some suits, ballast of gear, tanks, air, etc. The difference was that instead of using the LDS lead and weight belts, we used our pocket weight belts with weights I pulled from my weighted pull-up vest. They are a pound each and I think they are made out of iron with a glossy black paint. When I weighed them with my luggage scale, they were just over 15 lbs and 12lbs.

On the shore dive, my wife could not descend as she was too buoyant. She tried everything and the only way should could submerge is if I pulled her down with me and then she slowly floated back up.

So the only variables changing were the makeup of the weights and the column of water we were swimming in since it was a shore dive.

My question is: Does the composition or make up of the weight material (such as lead compared to iron) make a difference underwater if they weighted the same on the surface?

Or, is the underlying factor the column of saltwater (depth) under us?

Or, could it be she used an anchor line to lower her to a point on the boat dive where her wetsuit compressed enough?

What weighs more underwater? A pound of surface lead or a pound of surface feathers (or iron)?

 

[dkktsunami]

No scientific background here and I doubt that this would make enough difference ............. but the volume of iron necessary to match the same weight of lead would be more thereby displacing more water and creating a greater buoyant force. Am just guessing though. Someone with real knowledge will come along soon.

 

[gcbryan]

You are both new divers and that is why your wife had problems on that particular day. You didn't have problems and you were using different weights as well...correct?

 

[trailblazer1229]

Correct. We were both using new weights. I initially had some trouble getting down but worked it out.

Interestingly enough after doing some more internet searching I found this interesting piece of information.
http://freymanart.com/scale.htm

Turns, out it is a reverse experiment of the question.

 

[DennisW]

If you weigh purchased weights, you will find that they are not the weight they claim to be. A 3 lb weight will be around 2 1/5 lbs. This differs widely, so you can't just take a percentage off the weights you get from the LDS. So, if you used weights from the LDS and had 14 lbs (stated), I would bet they were actually about 2 to 3 lbs less than stated total unless the LDS makes their own weights. If you used weights that are actually weighed, then they are the weight you saw on the scale assuming the scale is Ok. Does this make any sense?

So about your problem, the weights you used in the second dive could be as much as 2 to 3 lbs different than the ones on the first dive. 2 to 3 lbs can make you have problems getting down.

So a pound of feathers weighs the same as a pound of lead, unless someone stamped 1lb on the lead and they lied.

 

[fire_diver]

Yes, there is difference, but I wouldnt think it would be enough of a difference to be noticable.

 

[fire_diver]

So a pound of feathers weighs the same as a pound of lead, unless someone stamped 1lb on the lead and they lied.

All bets are off when you change the medium you weigh them in. Don't forget the bouyancy factor invloved. One pound of lead and one pound of plastic would have VASTLY different "weight" underwater.

 

[ss7]

Lead and iron will give you different results. Dkktsunami was on target about the buoyancy effects. Lead will help your decent more than iron as its about 40% more dense.

If you had 15lbs of ice as weight, you would float like a champ, eh?

 

[Walter]

While there is a slight difference between buoyany of iron and lead, it's not enough for it to be a factor in your weighting. More likely reasons for the difference would be trapped air in the BC or the diver kicking up.

 

[Hatul]

I've never heard of iron diving weights. Wouldn't they rust with the slightest leak of the coating?