LP, HP or aluminum

[Genesis]

are BEASTS!

LP-104 104 CU.FT. 8.00 26.19 45 LBS -0.7 LBS

45 lbs empty!! (That's ~100 lbs for a pair of doubles, including bands, BEFORE the gas. Figure 115 full.)

HP-100 100 CU.FT. 7.25 23.94 31 LBS -1.4 LBS

That's ~70lbs for a pair of doubles, including bands, again before the gas.

30 lbs is a LOT! Its pretty close to carrying another AL80 in terms of weight....

Moving 100 lbs around on land is very un-fun. I've had to do it plenty of times and enjoyed it not one little bit, ever. Do you guys have a hand-truck for moving your tanks around on the docks and while on land? Gearing up has to be pretty fun too!

The difference in buoyancy for a pair is -1.4lbs.

HP-120 120 CU.FT. 7.25 27.87 36 LBS -0.4 LBS

These are longer (perhaps TOO long, which may be where the weight and balance complaint gets 'ya) but are only -0.4 empty, which puts the differential at 0.7 (in the positive direction)

Assuming you're NOT going to overfill, why would not the HP100s be a better choice than the LP104s, especially if you split them for open-water, non-pentration ocean dives and double them for penetration and deep ocean work?

Currently with an AL80 and a SS BP+OMS STA+Wing I wear 9lbs with a 3mil wetsuit and am neutral at the surface with a nearly-empty tank. If I went to a single HP100 I could remove 5lbs of that weight, which would still leave me with some ditchable weight, the kit would be lighter (all up) by a pound or two, and I gain 20cuft. If I double the HP100s and change the wing, all other things being equal, I deduct another 1-2lbs of weight, which leaves me near the "neutral with no belt" point (I might need 2lbs or so.) If I carry an AL40 stage for deco (close to neutral empty) with a 2lb regulator on it then I've not altered my weighting enough to matter.

This looks attractive (and will be a LOT more so in the fall/winter/spring around here when I need more exposure protection and thus even MORE weight!), but if I can't double the HP100s when I go into staged deco and other technical diving in the future then its a hell of a lot of money thrown down the drain.

Why would I not go the HP100 route here folks?

(I've talked to people who ARE tech divers about this, and their primary differentiating factor with the 104s are the assumption that I'm going to blow them to 3500 psi or so, which gives me ~130cuft of gas each ASSUMING that I'm doing Nitrox of some blend. If Trimix is in there then it changes to some degree, because Helium is less compressable (less volume for a given PSI is added), which means that the actual addition is probably not the full 32%.)

200 .vs. 260 cuft is significant, but to what degree? I can carry an extra AL40 stage and use it as travel gas; a Catalina 40 is 15lbs, which now takes me to close to the same gas capacity but saves me HALF of the weight burden of the 104s...

Is this one of those "people have always done it this way" things, or is there a real significant difference between doubling a pair of HP100s and LP104s?

 

[WreckWriter]

the PST 104s dive very sweet, bouyancy characteristics are right on for me. You're right though, on land or boat they're a heavy booger. One wouldn't be bad but doubles are dog heavy. I'll stick with them though.

One good reason to avoid the HPs is for gas diving. Many shops don't have a haskel for mix, so you may often end up with a short fill in HPs but can always get an overfill in LPs. Everyone here overfills 104s.

Tom

 

[spaz]

I want to know also. I double up High Pressure 120's and I have gotten some grief for it in cave country. Noone seems to have good answers for me though as to why. Even if I am useing mixed gases, I can keep the pressure down at 3000 and still have 103 cubic feet per tank. The tanks are long, but the have great bouyancy character.

I have watched and it is true, when in Florida Springs, most divers I have seen to date, dive LP tanks, and EVERYONE overfills them.

I dont dive only in caves and when you leave cave country you are stuck with LP fills if you have a LP tanks. But if you have the HP tanks,you can get them filled to rating almost anywhere. ( I have yet to find a shop that wont fill them).

 

[WreckWriter]

spaz once bubbled...
I dont dive only in caves and when you leave cave country you are stuck with LP fills if you have a LP tanks. But if you have the HP tanks,you can get them filled to rating almost anywhere. ( I have yet to find a shop that wont fill them).

I guess we're lucky here in that we have several tech oriented shops which will overfill the 104s.

I don't dive caves either, only wrecks.

Tom

 

[ScubaDan]

WreckWriter what would you do if you lived in an area that did not over fill tanks would you still use the LP-104's. I know My LDS would not over fill.

 

[WreckWriter]

ScubaDan once bubbled...
WreckWriter what would you do if you lived in an area that did not over fill tanks would you still use the LP-104's. I know My LDS would not over fill.

I think I would still dive the 104s. I'm used to them and I wouldn't like the long bottles.

I see your point though.

Tom

 

[WYDT]

Are LP 104's heavy? You bet! This is weight I can use though. Overfilled or not the LP 104's have great buoyancy characteristics for drysuit diving.

If you aren't diving dry you shouldn't be diving any type of steel tanks... unless you are POSITIVE you can EASILY swim them up from max depth with no gas in the wing.

There's a reason all the pro's use and recommend them.

With a trilam drysuit (DUI TLS 350), cannister light, aluminum backplate and minimal gas in the suit I am almost perfectly neutral in the water with nearly empty (LP 104) tanks. If I were to use lighter tanks I'd have to add weight somewhere to make up for it anyway so the weight saving is a moot point in the water.

Besides for those times that you can get them overfilled (all the time in cave country!) A set of doubles with nearly 300cu ft in them is very nice!!

DSAO!

 

[spaz]

My buddy dives LP 80's, and with the standard overfill (3500) in Florida she is at 116 Cubic ft, which nearly matches my double 120's, and makes for easy math on the thirds. She loves them.

Scuba Dan, You can find a shop to overfill, if that is your interest, what I have noticed is if there are backplates and wings on the wall with few or no jacket style BC's around. The shop will overfill. Just an observation, I guess the best thing is to just ask, but the shops that are more centered towards tech diving and not vacation diving will usually overfill.

 

[ScubaDan]

I have been to 3 of the 5 shops in the area two will not over fill and the other one would not even be able to fill a HP to 3500 I think they can only fill to 3100.

 

[Genesis]

I know the DIR-style issue with being able to swim up your kit, and agree with it, to a point.

BUT this assumes (and we all know what ASSuming does to you!) that you're going to use your drysuit as a redundant lift source.

Is not the issue that you have some kind of redundant lift source? Would not a lift bag (say, a 50lb one) provide that same redundancy?

Second, in a wetsuit environment the issue is primarily one of wetsuit compression and weight necessary to offset it during the first 30' or so of the water column. This is a MAJOR issue, but it is simply NOT changed by the tanks you're wearing.

If I wear my 3mil with a 5 mil jacket over the top of it, I need another 12 lbs of lead - or 21lbs total - to offset it. The tank(s), regardless of what they're made of, have roughly 6lbs of air in them (for 80s), 7-8 for 100s, etc.

An aluminum tank is ~4lbs positive when COMPLETELY empty, but obviously you would prefer that it not BE completely empty! If its down to 500lbs its 2-3 lbs positive.

An LP104 steel is close to neutral empty, as are the new "C" aluminum tanks. An HP100 or 120 is close to neutral empty as well (-1.4 or -0.7).

Double that and you still have less than 3lbs of negative contribution from the tank(s) empty. This is a "swing" of about 4lbs of negative contribution from a single tank, and about 8lbs of contribution from dual steels.

In both cases (for doubles) you have a 12-14lbs contribution from the gas, which goes away as you breathe it.

21lbs of "contribution" to your negative state at depth is from the neoprene in that case!

What the tank is made of has no relavence to the gas contribution to your negative state, nor to that from the neoprene of your suit!

Now if the issue is that I cannot safely drop my belt at depth in order to overcome a broken BC bladder, then that same issue attaches no matter how the negative state arises.

IMHO it simply does not matter how much weight is on the belt if I cannot safety drop it at depth, since doing so is not an ption.

This is one of the DIRisms that I have thought about quite a bit, and find JJs and GIs analysis deficient at best.

If the argument is that I must be able to ascend if my BC breaks, then the relatively small buoyancy shift from aluminum to steel tanks, as a percentage of the total contribution to the negative state, simply is not relavent to the argument.

We're talking about a contribution of at most 10lbs, while the suit and gas contribute (together) over 30lbs of negativity!

The tanks are the least of your problems in such a situation and are unlikely to matter. Swimming up 30lbs from 100'+ isn't going to be easy or even possible for most people, and that amount of the negative "balance" has no bearing on the tank's material.

The solution to this appears to be that if diving wet with doubles and significant exposure protection (where the negative buoyancy amount at depth exceeds your ability to swim it up until your suit regains its buoyancy) you need redundant lift capacity!

Since DIR eschews double-bladder BCs (and their reasons for doing so make sense to me) the obvious solution is a secondary lift device of some sort (e.g. a lift bag) to cover the possible failure of your BC bladder at depth.

Show me where my analysis is wrong on this one.

Second, you're missing another part of this.

Dry mass is irrelavent to underwater buoyancy. The simplest example is the HP100 is 31lbs dry but -1.4 when empty in the water, and the LP104 is 45lbs dry but -0.4 lbs when empty in the water.

If you are neutral with an AL backplate and suit at the surface with an empty tank with one, you'll be very close to neutral (within a pound or two) with the other.

However, when you get out of the water with one you'll be carting 100lbs around. The other will weigh only 70lbs! That 30lbs is a BIG DEAL when you're out of the water, and further, that's 30lbs that you have to deal with in inertia in the water as well - there is no free lunch on that one.

If you're a 150lb guy with either 80 or 110 lbs of gear on your back, that 30lbs makes a pretty significant (~12%) difference in your inertia underwater - that's mass you must accelerate when finning (or scootering). Since in-water resistance contributes to your effort as well and inertia only contributes when you CHANGE motion vectors, it won't make a 10 or 12% difference in gas consumption - but it might make a 5% one!

Show me why my analysis doesn't work here WYDT....