Yet another LP85 vs HP100 doubles question

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boriss

Contributor
Messages
213
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346
Location
South FL
# of dives
100 - 199
I'm about to buy my own set of doubles (vs. relying on instructor) and have been debating the Faber LP85's vs Faber HP100's. I'm in FL, so getting "cave fills" or relatively high pressure fills isn't a problem here even with LP's, but for my own peace of mind, I want to make sure I'm not making mistakes.

The Faber LP85 is a 13L tank and is actually 81.1cf @ 2640psi. The HP100 is a 12.9L tank and real capacity is 101.3cf @ 3442psi. Their volume is basically the same and they hold the same amount of gas at a given pressure. So all else being equal the HP100 should be the preferred tank as it's rated for the higher pressure and even if you fill it above stated pressure, it's more capable of dealing with said pressure. Here are my calculations:

1640491705370.png


They hold essentially the same amount of gas, so then the only other variable is weight/buoyancy characteristics. I'm not concerned about the buoyancy when full, partly because more gas weights more, so that's not a valid comparison. However when empty there's about a 3lb difference in buoyancy in water and weight on land. Two tanks and that's 6 lbs of additional weight. I know up north additional weight is preferred as it takes weight off your belt, but I'm not sure how I feel about that in FL.

So I guess the question are:
1. Is my logic sound? Anything that I'm overlooking?
2. Which tanks would you choose if weight didn't matter?
3. Would you still choose the same tanks with the buoyancy considerations? I have no need for extra weight.

Keep in mind, these will be back-mounted, not side-mounted. My stage/deco bottles will be aluminum. Lastly, although I'm not typically concerned about getting the LP85's overfilled to 3k+, I also don't want to be in a situation where I have to beg for it or risk not getting a full fill. I've been getting bout 3-3.2k on the LP95's, while the rented HP100's were filled to 3500+ without problems. Having said that, one of the shops told me they fill LP's to rated pressure.

Thanks in advance!

P.S. I don't care about the marginal difference in price between the two
P.S.S Looking to compensate for the added weight with a CF backplate
P.S.S.S. I believe the Faber are my only HDG (Hot Dip Galvanized) options available as new right now, if there are options I'd love to hear about them
 
My preferred set up is the twin LP85,s for my body size (5'10" 165 lbs) and exposure suits (wet and dry suits) they
trim out very nicely and ride closer to my back than 100's. As you point out they can be overfilled
if the fill operator is comfortable doing that to get the same or more gas than the 100's.
It really depends on the depth, your SAC rate, and type of dive being undertaken as to which set up would be better for you. I also dive twin LP 50,s as opposed to a single HP100 for many of the same reasons stated above.
I prefer the galvanized finish over the painted as the paint always gets nicked up.
I have been diving twin sets since 1995 in the Northeast and south Florida. If you can try to rent or
borrow to try them out to see what works for you.
 
My preferred set up is the twin LP85,s for my body size (5'10" 165 lbs) and exposure suits (wet and dry suits) they
trim out very nicely and ride closer to my back than 100's. As you point out they can be overfilled
if the fill operator is comfortable doing that to get the same or more gas than the 100's.
It really depends on the depth, your SAC rate, and type of dive being undertaken as to which set up would be better for you. I also dive twin LP 50,s as opposed to a single HP100 for many of the same reasons stated above.
I prefer the galvanized finish over the painted as the paint always gets nicked up.
I have been diving twin sets since 1995 in the Northeast and south Florida. If you can try to rent or
borrow to try them out to see what works for you.
Would you recommend LP85s for me (5'7", 140)? I dive warm water exclusively and its kinda between those and AL80s due to overweighting issues
 
Would you recommend LP85s for me (5'7", 140)? I dive warm water exclusively and its kinda between those and AL80s due to overweighting issues
At your size, I’d stick with 80s unless you’re in a drysuit. I did the overweighted thing in 85s and a wetsuit growing up and while some people have the ability to have a balanced rig with them, I’d probably pass.
Planned out from no tanks through anything you’d ever want to do: 80, then two 80 to have them doubled, then a 40, then a set of 85s/108s/etc, split the 80s, now you have everything for open water or cave diving up through backgas, two stages, and an oxygen bottle. Should you get through some OC mix training (or even ever venture down that path), and find yourself moving towards a CCR, the 80s are much more useful BO in the ocean than anything steel. Suit compression of wetsuits only worsens with depth, and finding your 3/5/7 being a skin at 35m is not a fun time to have a full set of 85s on your back.
 
if given the choice I will almost always go for HP tanks vs LP tanks for backmount doubles. Sidemount has some weird buoyancy and trim issues where lighter is usually better, but not generally so with doubles.
Tank length is not something brought up yet and while it is only about 3/4 of an inch with the Fabers, it is there and with the HP100's being a bit shorter that's better for most.

@Dominick Marino the OP stated correctly that the HP100's and LP85's hold functionally the same amount of gas when filled to the same pressure *the 85's hold about 1% more gas, but that's not significant*.

@Ian Fatzinger since you're in Hawaii I would stick with AL80's due to the climate more than anything. Trying to keep steel tanks dry and free of rust out there is going to be a losing battle.
 
At your size, I’d stick with 80s unless you’re in a drysuit. I did the overweighted thing in 85s and a wetsuit growing up and while some people have the ability to have a balanced rig with them, I’d probably pass.
Planned out from no tanks through anything you’d ever want to do: 80, then two 80 to have them doubled, then a 40, then a set of 85s/108s/etc, split the 80s, now you have everything for open water or cave diving up through backgas, two stages, and an oxygen bottle. Should you get through some OC mix training (or even ever venture down that path), and find yourself moving towards a CCR, the 80s are much more useful BO in the ocean than anything steel. Suit compression of wetsuits only worsens with depth, and finding your 3/5/7 being a skin at 35m is not a fun time to have a full set of 85s on your back.
if given the choice I will almost always go for HP tanks vs LP tanks for backmount doubles. Sidemount has some weird buoyancy and trim issues where lighter is usually better, but not generally so with doubles.
Tank length is not something brought up yet and while it is only about 3/4 of an inch with the Fabers, it is there and with the HP100's being a bit shorter that's better for most.

@Dominick Marino the OP stated correctly that the HP100's and LP85's hold functionally the same amount of gas when filled to the same pressure *the 85's hold about 1% more gas, but that's not significant*.

@Ian Fatzinger since you're in Hawaii I would stick with AL80's due to the climate more than anything. Trying to keep steel tanks dry and free of rust out there is going to be a losing battle.
Thank you both for the information. Which manifold/bands should I buy? The DGX ones are all out of stock and the rest seem double the price
 
LP's any day for me over HP. The HP s are going to be harder to fill if your in a pinch on time and not allowing them time to cool down and top off.
 
Thank you both for the information. Which manifold/bands should I buy? The DGX ones are all out of stock and the rest seem double the price
Wait for DGX, search locally, or wait for a dt to pop up here, Craigslist, or one of the various Facebook groups. Randy at Pirahna also tends to be pretty responsive, but even Blue Steel has had difficulty fulfilling orders.
 
When I faced this decision, the price difference was not marginal (HP was nearly 40% more expensive). Outside of that, I chose LP85s because narrower, lighter on land, and perfectly weight me in the temperate conditions I typically dive (drysuit, medium layers). (As an aside, I will also likely explore side mount at some point, and I have to think being closer to neutral is better for that application.)
 
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