Buoyancy question

[Bob DBF]

I underweighted myself once to try it out to see it was like, just practicing in the shallows. It was not that easy!

Sometimes I think people say that so they can sell the noobies steel tanks instead of aluminum tanks, because steel tanks are more expensive... The salespeople I have met are always trying to sell me the most expensive gear...because they think I don't know any better... "Here, buy this expensive one, I'll will make diving easy!" seems to be a common theme...

Significantly over-weighting yourself will cause more problems as you will have a good sized air bubble in your BC which will expand and contract with depth changes, changing your buoyancy a lot in shallow water. Under-weighted your BC will be empty and you will be changing your buoyancy with your lung volume, which will work if you aren't too light.

Salesmen are paid to make sales, and some have lower ethical standards than others, regardless of what they are selling. In my experience, what makes diving easy is practice, even if you are using some [-]crap[/-] less than optimal gear, its not a big deal once you get used to it.


Bob

 

[Dive Right In Scuba.]

I underweighted myself once to try it out to see it was like, just practicing in the shallows. It was not that easy!

Sometimes I think people say that so they can sell the noobies steel tanks instead of aluminum tanks, because steel tanks are more expensive... The salespeople I have met are always trying to sell me the most expensive gear...because they think I don't know any better... "Here, buy this expensive one, I'll will make diving easy!" seems to be a common theme...

As the Bible says, for everything there is a season, and a time for every purpose under Heaven--or was that Pete Seeger?

I own 12 tanks, 6 steel and 6 aluminum, and I use the right tank for the right job. When I am diving in your area--and I do a fair amount of diving in your area--I usually use steel. Maybe that retailer is trying to get you to buy the most expensive things. Maybe that retailer is trying to give you the very best advice for the diving you will do. Maybe both are true.

 

[Steve_C]

It ain't just the weighting that counts. For trolls like myself (5'7") I find the AL-80s, of which i have two, to be a bit long. Definitely divable but a bit long. My HP100s on the other hand are shorter and trim much more naturally. For short folks a shorter tank can be more comfortable and the extra gas and weight issues a bonus.

 

[seeker242]

As the Bible says, for everything there is a season, and a time for every purpose under Heaven--or was that Pete Seeger?

I own 12 tanks, 6 steel and 6 aluminum, and I use the right tank for the right job. When I am diving in your area--and I do a fair amount of diving in your area--I usually use steel. Maybe that retailer is trying to get you to buy the most expensive things. Maybe that retailer is trying to give you the very best advice for the diving you will do. Maybe both are true.

I think it's usually the former. Being a salesperson myself, I'm finely tuned to the BS spiel! I use the same techniques on my customers, Ha! I'm not knocking steel tanks, I think they're great. I plan on getting a couple myself. But the idea that they make safety stops easier to hold, the BS detector is ringing!

 

[spectrum]

Hi All,

I have a question regarding buoyancy differences of Al and steel tanks. First, I know that differences in buoyancy characteristics will effect trim so this question ignores trim. From what I have been reading, most people consider the buoyancy characteristics of steel to be better than Al. The reason I have most often seen stated is because an Al tank is positively buoyant when empty. My question is why is this even a factor?
Jim

You will find a detailed explanation here.

Pete

 

[ljpm]

You will find a detailed explanation here.

Pete

From above link:

"However it is relatively heavy for the air it contains and since it becomes positively buoyant by about 4 pounds by the end of a dive you need to wear weight just to hold the cylinder down to allow for a proper safety stop and orderly ascent. "

This sentence can be misleading. It gives the impression you need to carry extra weight, beyond being properly buoyant at the beginning of a dive. If you start a dive properly buoyant with either a steel or an aluminum tank you will experience the same buoyancy at the safety stop. In order to achieve a proper buoyancy you will require 4 more pound if you are diving with an aluminum tank. This fact seems to get twisted in a number of the post I have come across on the internet. Most likely resulting from people paraphrasing statements like above with out fully understanding and getting them slightly wrong.

All cleared up now. Thanks guys.

 

[Dive Right In Scuba.]

I plan on getting a couple myself. But the idea that they make safety stops easier to hold, the BS detector is ringing!

The times I find a difference in buoyancy characteristics are when diving sidemount. I normally use Worthington LP 85s when I dive sidemount, but they are no loner being made. I recently did some sidemount diving with aluminum 80s for the first time, and as we got near the end of the dives, the problem of the butts of the tanks going sky-ward was significant. Because I was in a cave, I had to be horizontal, which is the real reason for the problem. This is a well known issue for sidemount divers.

If I were diving in the open water while back mounted, and if I were especially in a more vertical trim, it would not be a problem at all.