Tanks: 80's versus 100's

[TyTy]

Im going diving this coming Monday (EXCITED!) and am an air sucker/newbie. My girlfriend uses almost no air. My dive instructor suggested to use 100's and have her stay on the 80's, might get our bottom times closer together.

Anyway, I emailed the dive operator who replied that he had some 100's I could use but that they were "much" heavier but no more negative. (So I'll have to use the same amount of lead).

My question is how much heavier? (Could he mean his are steel 100's versus the aluminum 80's? If that was the case steel 100's would be much more negative than an AL 80 wouldnt it?)

Also, with the extra weight but no more negativeness, will I just expend more energy swimming with them and negate the extra bottom time?

So which one to use is the question.

 

[CD_in_Chitown]

You need to get the op to clarify what kind of tank it is (LP95, HP100, 104, etc) so that you can plan better. He might be talking about anything from a 90 to a 112, the buoyancy characteristics are going to vary greatly in that range.

 

[jonnythan]

If it's no more negative it's almost certainly an Al 100. They're only about 9 pounds heavier on land so it shouldn't be that much of a problem.. you do get about 30% more gas.

 

[spectrum]

Anyway, I emailed the dive operator who replied that he had some 100's I could use but that they were "much" heavier but no more negative. (So I'll have to use the same amount of lead).

My question is how much heavier? (Could he mean his are steel 100's versus the aluminum 80's? If that was the case steel 100's would be much more negative than an AL 80 wouldnt it?)

I don't know what steel 100 he could have that wouldn't be at least 4-5 pounds better than an AL80.

It sounds like he dosen't have a firm grasp of weight vs. bouyancy.

http://www.huronscuba.com/equipment/scubaCylinderSpecification.html

Also, with the extra weight but no more negativeness, will I just expend more energy swimming with them and negate the extra bottom time?

So which one to use is the question.

That's where weight (raw mass) comes into play. Yes it will cost you some of the extra air just carrying the capacity. I was recently told that I could dive a 72 or an 80, to expect the same outcome. I have a hard time believing it's that cut and dried but I'm sure the truth is somewhere in between.

FWIW her AL80 is only going to be 77.? CF, you will probably have something closer to a true 100. Both subject to cooling losses. Try to make sure yours is topped off after cooling.

How does she feel about diving a 72?

Recently someone mentioned spending some time on the light users safe second to conserve your air. Might work out if you're dubbing around watching critters.

Pete

 

[Don Burke]

I agree that it is probably an AL100, and likely to be the Luxfer AL100.

You will be about ten or eleven pounds heavier in air and will start the dive a bit over a pound heavier in water than you would be with an AL80 due to the extra gas.

The empty bouyancy of an AL80 and an AL100 are pretty close. By the charts, you would take off a pound of weight. I would leave the weight alone for now and check it at the end of the first dive.

Swimming effort will go up just a bit. I doubt you will notice that change.

 

[Firefyter]

I agree that it is probably an AL100, and likely to be the Luxfer AL100.

You will be about ten or eleven pounds heavier in air and will start the dive a bit over a pound heavier in water than you would be with an AL80 due to the extra gas.

The empty bouyancy of an AL80 and an AL100 are pretty close. By the charts, you would take off a pound of weight. I would leave the weight alone for now and check it at the end of the first dive.

Swimming effort will go up just a bit. I doubt you will notice that change.

I own and dive a Luxfer AL100, and Don is right on the money. A little heavier to walk around with, but not much difference in water, other than volume.

 

[TyTy]

I own and dive a Luxfer AL100, and Don is right on the money. A little heavier to walk around with, but not much difference in water, other than volume.

Sweet, so I guess I will take him up on the 100's and use em. My dive instructor suggested using 100's any time they are available so I assumed he had in mind the extra weight its just that when this dive operator said the 100's he had were "much" heavier I wondered if I would come out better.

My buddy (girlfriend) gets cold fast so she dosent mind coming up a little earlier for my air sucking. Ill get better but right now with a 3MM farmer john and 3MM core thing I was using 28lbs in saltwater. I will be using my 3MM 1 piece on this dive so that will be less weight, less air used, etc... I have the problem where I need lots of weight to get down and then once Im down I have problems with bouyancy and fight that, thus use more air.

Anyway, Ill get it worked out, loose some of the weight and work on breathing technique.

Thanks for the help everyone, Ill use the 100's.

 

[Mr. Schnitzer]

I'm going to try getting a 100 since I suck down air faster than my fiancee (She's tiny)... thanks for the tip TyTy

 

[scubafool]

Just remember to be somewhat conservative when deciding at what pressure to start heading for the surface. If you need to share air with her out of her tank, considering that you are the heavier breather, she needs to turn the dive with enough gas in her tank to get the both of you back up safely.

 

[Mo2vation]

I'm going to try getting a 100 since I suck down air faster than my fiancee (She's tiny)... thanks for the tip TyTy

My wife (not tiny, just not real strong) was a diver before me. I got her an HP80, and got me an HP100. This lasted for a few years, and now I use less/same gas as her. So I ended up eBaying the 80, moved her into my 100 and got me a 130.

---
Ken