Length or Width...Does Size Matter?!?

[MacLeod]

Looking at PST's new E-series, I would really appreciate hearing from people as to what they have found to be more beneficial/detrimental when comparing two tanks of comparable volume but different length and width.

Specifically, PST's E7-120 and E8-119 (3442 PSI service pressure)

E7-120:
Diam: 7.2 Length: 28 Wt: 36.6lbs BuoyEmpty: -1.3 Full: -10.3

E8-119
Diam: 8.0 Length: 24 Wt: 39.3lbs BuoyEmpty: -3.3 Full: -12.2

I am 6'3" so the 120's length is not a major issue.

Being only 1 cuft in volume difference and close in weight, it seems like the real difference lies primarily in diameter. Some might say the smaller diameter (longer tank E7) gives a better profile others might say the shorter tank (larger diameter E8) is more maneuverable or less likely to get hung-up on things when moving through wrecks.

I would like to use these tanks for NJ wreck dives as singles to begin with (I am looking to buy 2 to start) and *possibly* double them up in the future. Which do you feel would be the best tank to choose?

The E8-130
Diam: 8.0 Length: 25.56 Wt: 42.2lbs BuoyEmpty: -4.8 Full: -14.6

The E8-130 I know is popular with cave divers as the previous LP-104...but seems like it might be just a bit big.

Thank you for your help...I really appreciate it.
Jon

 

[Rick Murchison]

My personal trim characteristics favor longer tanks, even though I'm only 5'8"... I seen where others on this board who are taller are quite happy with shorter tanks, so there doesn't seem to be any hard & fast rule to go by - other than getting your hands on some and trying 'em out.
Good luck,
Rick

 

[LUBOLD8431]

Is there any way you can dive these cylinders before you buy them??? Any of your buddies that you dive with have these cylinders??? you might want to keep things the same. You and your buddy having the same cylinders... Keeps things easier for planning gas, and turnaround.

As far as the choice between those cylinders, I find that the 119's are too short for me. You, being about four inches taller than me, would really notice it, i think. The 119's, when you strap into them, wont be hitting the bench when you are sitting down on the boat. Which means, that it will be uncomfortable kitting up and taking off the cylinnders. I think you might be more comfortable with the 120's. I would try to test dive them though, if possible...

 

[FredT]

This is mostly a linear function of wetted surface area. Surface area is 3.1416 * D * L + (3.14*D^2/4) using flat planes to approximate the spherical ends of a steel tank less boot.

The choice after that is one of nimbleness and trim.

FT

 

[MacLeod]

Rick, LUBOLD8431 and FredT really great insight and advice...thank you very much!!

Seeing that tank length and width don't necessarily follow a height standard...and reminding me of the cylinder length in relation to the boat bench scenario(I'd forgotten seeing that problem a couple of times in the past)...all very helpful.

FredT the "drag formula" is great...I love calculating that kind of stuff.

I wish I could borrow a couple of these tanks to try out. Unfortunately I don't know anyone locally who uses them, let alone rents them. All the more reason why I really appreciate your help!

Based on what has been said, I think I will probably go with the E7-120s. The only question I have is head clearance. I mean, will I be banging my head on the back of the valve when I look up?

Thank you all again!!

Jon

 

[MacLeod]

Oh boy...confused again. Was just reading an old post where a number of people are talking about the old LP104s (now the E8-130s I mentioned above)...perhaps I shouldn't rule these out yet ( http://www.scubaboard.com/showthread.php?s=&threadid=16314&perpage=15&display=&pagenumber=1 ).

Please, any thoughts? This is really starting to drive me crazy...it is so tough to decide sight unseen.

*Thank you*.
Jon

 

[pescador775]

Are you using a boot? I've never used them but some people like to stand their tank on something to aid in donning. In this case, with your height, a longer tank would be better. This topic of 'tank balance' comes up regularly which puzzles me. I can dive any tank or double set around and hardly notice any difference except in extreme cases such as an aluminum tank versus a Faber or Heiser HP tank in which case the bouyancy differences are very pronounced. Triple tanks may cause a slight trim problem because of the heavy manifold but not many people would be using these. Personally, I would avoid the aluminum tanks for buoyancy reasons, and the eight inch steel tanks which have significant drag and are roly poly on the surface. Also, since they project upward out of the water they will hold the diver down to some degree when he is stroking on a snorkel.

 

[HarleyDiver]

I dive both a 8" LP98 & a 7.25" HP120.
I don't find all that much difference underwater but I find some dive boats are not set up to handle oversize tanks.
I have had some that can't take the 8" tank with a boot on it.
Another had clips that would not let me set up my 120 at the hieght I wanted.

Tanks are a lot more trouble OUT of the water than in, so make getting them to & from the dive part of your decision.

 

[Genesis]

This is a very real issue and one to consider.

Many private boats have "roll control" racks. There are two inserts - one adjusts, the other does not. However, "one adjusts" is a bit less than honest, since to "adjust" you have to take the rack out of the track, and that's a PITA.

Bottom line on my boat is that if you have 8" tanks you're putting them in the Salon, and had better bring some kind of tank caddy (e.g. one designed for a car to keep them from rolling around) which is a PITA for you.

My racks are all set up for the 7.25" common "standard", which encompasses AL80s, HP100s, HP120s, etc.