Question Picked up a pair of Faber LP95s, do I need to tweak my weighting for buoyancy?

[inquis]

But the buoyancy math with the LP95 is confusing

Happy to elaborate if there's a specific question?

Perhaps it's the negative values that are tripping you up. Starting with the LP95's buoyancy of +1.7 lb, you would have to strap 1.7 lbs of lead on it for it to be neutral (by itself) and another 0.6 lb to result in a buoyancy of -0.6 lb. This then matches the buoyancy of the HP100 (which we looked up). You had to add 1.7+0.6 lb or 2.3 lb to make them match.

Since 18 lb on your belt let's you dive with the HP100, it would also take 18 lbs on your belt for you to dive an LP95 with 2.3 lb strapped on it. But you've got a perfectly good belt, so you might as well put that 2.3 lbs on it instead of the tank. Rounding heavier, that's where the "add 3 lb" or "you'll need 21 or so" advice up thread comes from.

 

[inquis]

I shouldn’t have buoyancy issues with these vs. aluminum if I get the weighting down?

Same consideration applies. An AL80 's buoyancy is +4.4 lb. The difference from the -0.6 lb HP100 is 5 lbs. If 18 lb works with the HP100, an AL80 will require 18+5 or 23 lb.

Now, there is a little difference between these various tanks in where the "balance point" or "center of mass" lies, but you need only worry about that if you can't stay horizontal even though being neutral overall (not changing depth). (Usually your feet will sink and head rises.) The total weight can be correct, but you might need to move some of it up on your body for better balance. This aspect is known as "trim" rather than "buoyancy" or "weighting", in spite of the fact weights and buoyant forces impact them all.

I do apologize if you already know all this. I'm just guessing at how in-depth your OW instruction was, but too often none of this is covered.

 

[jellycatsdad]

Happy to elaborate if there's a specific question?

Perhaps it's the negative values that are tripping you up. Starting with the LP95's buoyancy of +1.7 lb, you would have to strap 1.7 lbs of lead on it for it to be neutral (by itself) and another 0.6 lb to result in a buoyancy of -0.6 lb. This then matches the buoyancy of the HP100 (which we looked up). You had to add 1.7+0.6 lb or 2.3 lb to make them match.

Since 18 lb on your belt let's you dive with the HP100, it would also take 18 lbs on your belt for you to dive an LP95 with 2.3 lb strapped on it. But you've got a perfectly good belt, so you might as well put that 2.3 lbs on it instead of the tank. Rounding heavier, that's where the "add 3 lb" or "you'll need 21 or so" advice up thread comes from.

I was reading off the Huron Scuba list my LP95s are -1.2lbs buoyant when empty with valve installed, but others I saw say it’s +1.6lb buoyant. Which was one thing I was confused about. Faber has it .7kg buoyant - are they accounting for an installed valve as well?

Since the LP95 is a fair bit heavier than the HP100, I was hoping to carry less lead - but it looks like since it is a physically bigger tank that displaces more water, I’m gonna need to carry more lead. But the trade off is I’ll have more air if a shop does overfill it. Not sure if California shops do the same “cave fill” as in Florida.

 

[jellycatsdad]

Same consideration applies. An AL80 's buoyancy is +4.4 lb. The difference from the -0.6 lb HP100 is 5 lbs. If 18 lb works with the HP100, an AL80 will require 18+5 or 23 lb.

Now, there is a little difference between these various tanks in where the "balance point" or "center of mass" lies, but you need only worry about that if you can't stay horizontal even though being neutral overall (not changing depth). (Usually your feet will sink and head rises.) The total weight can be correct, but you might need to move some of it up on your body for better balance. This aspect is known as "trim" rather than "buoyancy" or "weighting", in spite of the fact weights and buoyant forces impact them all.

I do apologize if you already know all this. I'm just guessing at how in-depth your OW instruction was, but too often none of this is covered.

Yea, I already carry some of my weight on my upper cam band as trim - a 5lb soft weight and whatever small 1-2lb increment I need to add to my total. Most of my weight is on a weight belt, about 10-20lbs in 5lb weights. I’m already seeing an improvement using a BPW vs a “regular” BC for this - I’ve gotten my trim down with the HP80/100. I haven’t dove an Al80 too many times to test this out.

 

[lexvil]

It’s to late since you have the 95’s but the best tank to have for plus fills is the LP 85, they are often mistaken for AL 80’s and get hit to 3200 a lot and sometimes they get mistaken for HP 100’s and get 3500 +, stay close by so you can stop them from bleeding them back down.

95 are not mistaken for anything but farm animals. They are good tanks so dive them.

 

[inquis]

I was reading off the Huron Scuba list my LP95s are -1.2lbs buoyant when empty with valve installed, but others I saw say it’s +1.6lb buoyant. Which was one thing I was confused about. Faber has it .7kg buoyant - are they accounting for an installed valve as well?

Since multiple other lists have said the 95s are +1.7 lb -- including Faber themselves (0.77 kg = 1.7 lb) -- I infer that Huron is in error. Other lists do say "with valve", which would imply the Faber list is also with a valve.

You're also starting to understand why LP95s are not super popular. They are heavier to start with AND require still more lead on top of that. HP100s hold more gas at rated pressure and your total load walking to the water is almost 5 lbs less. That said, a $$ deal can flip the script regarding which is better overall for you. I hope you enjoy diving them!

 

[jellycatsdad]

Since multiple other lists have said the 95s are +1.7 lb -- including Faber themselves (0.77 kg = 1.7 lb) -- I infer that Huron is in error. Other lists do say "with valve", which would imply the Faber list is also with a valve.

You're also starting to understand why LP95s are not super popular. They are heavier to start with AND require still more lead on top of that. HP100s hold more gas at rated pressure and your total load walking to the water is almost 5 lbs less. That said, a $$ deal can flip the script regarding which is better overall for you. I hope you enjoy diving them!

Well, I did get them for a deal. They do need a bit of work(hydro/visual, new valves and tumble/O2 clean). I’ll dive them. if I find I can’t deal with them, I’ll sell them to finance a pair of HP100s.

 

[Tanks A Lot]

Which was one thing I was confused about. Faber has it .7kg buoyant - are they accounting for an installed valve as well?

I highly doubt Faber would account for a valve installed. None of the cylinder manufacturers ever do so on their spec sheets. If you think about it, it wouldn't make sense either, as variability can be substantial in valves. A big Y-Valve will be a lot heavier than a small vertical "rebreather" valve.

Faber gives only this on their drawings database:

-Dimensions, weights, buoyancies and water capacity are nominal
-Availability of all cylinders to be confirmed by Faber
-All cylinders are manufactured from steel plate with shaped bases ( unless specified "concave base")
-"Real Weight"=EmptyWeight+ Buoyancy Empty
-For DOT3AA (USA) cylinders the 10% overfilling is allowed if a plus (+) symbol is marked on the dome of the cylinder.
-Do not exceed the allowed working pressure (W.P.).
-Drawing prints are available at www.divefaber.com selecting Dive Faber Dbase & Drawings from menu
-See Legal Disclaimer at www.divefaber.com/legal.htm

 

[jellycatsdad]

I highly doubt Faber would account for a valve installed. None of the cylinder manufacturers ever do so on their spec sheets. If you think about it, it wouldn't make sense either, as variability can be substantial in valves. A big Y-Valve will be a lot heavier than a small vertical "rebreather" valve.

Faber gives only this on their drawings database:

Yea, that’s a good point. The LDS will be installing new Thermo Pro valves that can be converted between DIN and yoke with an insert, someone here weighed it out to 1.5lb. So I might be closer to neutral unless the tank’s size needs to in account?

 

[inquis]

And yet there are spec sheets that say with a valve. Presumably a "normal" valve so the spec sheet will not be nearly as far off as no valve.