Landlocked123
Contributor
Getting ready to move to doubles. Torn between the two above. I dont plan on a dry suit so will be diving 7 mill in cold water. OMS Steel backplate. Any input?
Double LP85's or HP100 - Diving Wet-Steel Backplate
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With a wetsuit, I'd go with double AL80's. Diving steel tanks with a wetsuit can open yourself up for a bunch of issues if you lose your wing.
As others will probably chime in, diving steel doubles + steel backplate with wetsuit not always greatest idea without some redundant form of buoyancy. You'll likely want to carry a lift bag for redundancy or look at dual bladder wing (not my favorite) but will work fine.
You'll likely find yourself overweighted with either double HP100s or LP85s. You may also want to forgo steel plate and go with aluminum. In most cases I'd almost always go with steel backplate but you might find an aluminum better with a wetsuit.
Otherwise the size of HP100s/LP85s (length, diameter) are somewhat similar. LP85s being 7 inch diameter versus HP100s being 7.25 inches. HP100s are also two inches longer than most LP85s. I find they trim out very similar as well.
HP100s are going to be more negative so if you're only going to be diving wetsuit then I'd probably recommend LP85s. With a modest overfill of the LP85s (if your local shop will do it) you'll have just as much gas as the HP100s.
Personally I'm a big fan of HP100s. I own multiple sets, mostly PSTs. If your shop is not willing to overfill LP85s (outside of cave country, may be a problem unless you're doing your own fills) then HP100s in theory will give you more gas. 170 vs 200 cu of gas provided your shop will give you a proper high pressure (~3500psi fill). Most shops have no trouble filling 3500psi now-a-days unless they're in the habit of doing really hot fills and not topping them off. Pretty much every shop on planet can do a 2600psi easily.
EDIT: Beaten by @lewisevans
EDIT: scuba tank specifications
You'll likely find yourself overweighted with either double HP100s or LP85s. You may also want to forgo steel plate and go with aluminum. In most cases I'd almost always go with steel backplate but you might find an aluminum better with a wetsuit.
Otherwise the size of HP100s/LP85s (length, diameter) are somewhat similar. LP85s being 7 inch diameter versus HP100s being 7.25 inches. HP100s are also two inches longer than most LP85s. I find they trim out very similar as well.
HP100s are going to be more negative so if you're only going to be diving wetsuit then I'd probably recommend LP85s. With a modest overfill of the LP85s (if your local shop will do it) you'll have just as much gas as the HP100s.
Personally I'm a big fan of HP100s. I own multiple sets, mostly PSTs. If your shop is not willing to overfill LP85s (outside of cave country, may be a problem unless you're doing your own fills) then HP100s in theory will give you more gas. 170 vs 200 cu of gas provided your shop will give you a proper high pressure (~3500psi fill). Most shops have no trouble filling 3500psi now-a-days unless they're in the habit of doing really hot fills and not topping them off. Pretty much every shop on planet can do a 2600psi easily.
EDIT: Beaten by @lewisevans
EDIT: scuba tank specifications
Last edited:
I got LP85s filled to 3300-3500 psi last week at two different dive shops in SE Florida (for a total of ca. 210-225 cf in doubles). I guess those weren't quite cave fills, but it wasn't in cave country, either.
Caveeagle
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StefinSB
Contributor
My Faber lp 85 is about 0.5 pounds positive when empty w/ valve. I use them as doubles with a drysuit mostly by even in a 7 mm I need a little bit of additional lead. With double HP 100 I would for sure be overweighted with a steel plate. Worthington LP 85 are -1 pound empty so you may want to specify which LP 85s you are talking about.
I dive a set of steel HP 100s in a wetsuit. As others have said, they are HEAVY! I have a SS backplate, and I find that this rig works well while wearing my 8 mm semi-dry. I'm still a little heavy at the end of the dive, but not bad. I'm going to pick up an aluminum BP to shed a couple of pounds with this rig when I move to my thinner, warm water wetsuit. A redundant lift source is indeed a good idea with double 100s.
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@macado where are you getting those numbers from? That is only true with the Worthington LP85's against normal HP100's or the newest FX100's *which are closer to 120's than 100's* from Faber against their LP85's. "normal" HP100's are 2" shorter and bigger around than LP85's, but anyway, that's neither here nor there.
To the OP, your configuration is not a safe diving configuration. I'll just go straight to the point, and here is why. 7mm suits have no business doing deep diving due to the suit compression, especially if it is a farmer john. You also shouldn't dive tanks that are that big in a wetsuit because at depth the odds of you being able to kick them up from the bottom in the event of a wing failure are basically 0. Compound that with the fact that a steel backplate will grossly overweight you to the point that it is idiotic, you're asking for trouble. Your wing has to do 2 functions. Hold the rig at the surface, and compensate for buoyancy. Let's do some math.
Bands-4lbs
Manifold/valves-6lbs
Backplate-6lbs
Regulators-4lbs
Weight of gas-roughly 16lbs
Buoyancy of tanks-anywhere from -7 with Worthington HP100's to 0 with LP85's
You are at a minimum of -36, likely closer to -40lbs at the surface.
Wetsuits have a buoyancy compensation of roughly 3:1. I.e. 1lb of wetsuit at the surface requires about 3lbs of lead to sink. 7mm's are roughly 5-7lbs for most people, so 15-20lbs of lead to get it to sink. You are now at a minimum of 51lbs, potentially up to 60lbs lift requirement out of your wing. You are starting the dive naturally overweight because the the ballast of the empty rig exceeds the requirements of your exposure protection unless you're diving LP85's in a 7mm farmer john, in which case it is still not a safe configuration due to the buoyancy swing. IF you're going to do this anyway, at least do it with a neutral or close to it plate instead of stainless steel, especially if you go with HP100's where you are going to be close to 5lbs overweighted even with a kydex/aluminum plate.
Also remember your exposure. You define cold water, but don't say how cold. 100ft with HP100's on a normal diver, in open water, will net you well over an hour of bottom time, which at depth in a 7mm means you will get COLD, and quite possibly dangerously cold increasing your likelihood of getting DCS. Drysuit in deep cold water diving is a safety concern so please do yourself a favor and consider purchasing one....
To the OP, your configuration is not a safe diving configuration. I'll just go straight to the point, and here is why. 7mm suits have no business doing deep diving due to the suit compression, especially if it is a farmer john. You also shouldn't dive tanks that are that big in a wetsuit because at depth the odds of you being able to kick them up from the bottom in the event of a wing failure are basically 0. Compound that with the fact that a steel backplate will grossly overweight you to the point that it is idiotic, you're asking for trouble. Your wing has to do 2 functions. Hold the rig at the surface, and compensate for buoyancy. Let's do some math.
Bands-4lbs
Manifold/valves-6lbs
Backplate-6lbs
Regulators-4lbs
Weight of gas-roughly 16lbs
Buoyancy of tanks-anywhere from -7 with Worthington HP100's to 0 with LP85's
You are at a minimum of -36, likely closer to -40lbs at the surface.
Wetsuits have a buoyancy compensation of roughly 3:1. I.e. 1lb of wetsuit at the surface requires about 3lbs of lead to sink. 7mm's are roughly 5-7lbs for most people, so 15-20lbs of lead to get it to sink. You are now at a minimum of 51lbs, potentially up to 60lbs lift requirement out of your wing. You are starting the dive naturally overweight because the the ballast of the empty rig exceeds the requirements of your exposure protection unless you're diving LP85's in a 7mm farmer john, in which case it is still not a safe configuration due to the buoyancy swing. IF you're going to do this anyway, at least do it with a neutral or close to it plate instead of stainless steel, especially if you go with HP100's where you are going to be close to 5lbs overweighted even with a kydex/aluminum plate.
Also remember your exposure. You define cold water, but don't say how cold. 100ft with HP100's on a normal diver, in open water, will net you well over an hour of bottom time, which at depth in a 7mm means you will get COLD, and quite possibly dangerously cold increasing your likelihood of getting DCS. Drysuit in deep cold water diving is a safety concern so please do yourself a favor and consider purchasing one....
what Lewis said in post #2!
Everyone else has told you why the configuration isn't a good idea, what they are saying is you need to use an aluminum back-plate (not steel) and possibly a redundant wing (or drysuit). I do have a quick question though, salt or fresh water?
I probably wouldn't fret too much about double LP85's in salt water with a 7mm wet-suit and aluminum plate. There's no way I'd consider it in a steel plate. Fresh water? I'm going to want a redundant wing or a drysuit.
I probably wouldn't fret too much about double LP85's in salt water with a 7mm wet-suit and aluminum plate. There's no way I'd consider it in a steel plate. Fresh water? I'm going to want a redundant wing or a drysuit.
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