• Welcome to ScubaBoard


  1. Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

    Benefits of registering include

    • Ability to post and comment on topics and discussions.
    • A Free photo gallery to share your dive photos with the world.
    • You can make this box go away

    Joining is quick and easy. Login or Register now by clicking on the button

Going from AL100, salt, no wet suit ---> HP100, fresh, 5mm... advice please.

Discussion in 'Basic Scuba Discussions' started by noj3333, Sep 25, 2016.

  1. noj3333

    noj3333 Solo Diver

    # of Dives: 100 - 199
    Location: Albany, New York
    862
    393
    63
    Ok, so I could use some advice from the board.

    For a few different reasons I’m looking to get geared up to do some local diving come next Summer. I live in New York so that would mean Dutch Spring and the St. Lawrence River. From my limited experience I know I have a ‘higher than normal’ SAC rate. I don’t have exact calculations, but I usually have less PSI than my fellow divers when I return to the boat post dive... and I'm using 100's where my peers are using 80's.

    With my higher SAC rate I was going to use/buy HP100 tanks. With the HP100’s I’d hope to gain some additional volume (over AL80/100's), plus I’d be able to shed a few pounds of lead. I plan on diving wet with a 5mm suit, gloves, hood, boots.

    My BC is a BioLite (Oceanic), with 38lbs of lift. All my previous dives have been in salt water and I need 24lbs of lead, with no exposure protection, using AL100's.

    I know I’d drop some lead going from salt to fresh water, but I have no idea how much to expect. Any ideas from experience?

    Does my rig (HP100, 5mm wetsuit, 38 lbs. of lift) seem like it would be safe? Clearly, I would have limited options of my BC failed… do you folks think I’d have a shot a being balanced with this set up?

    Thanks, and any other feedback on my situation is appreciated.
     
  2. rongoodman

    rongoodman ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Albany, NY
    4,960
    1,616
    113
    You could try the Estimated Diving Weight Calculator | DiveBuddy.com. Enter the set-up you're using now and see how its suggestion compares to what you're actually using. You can then adjust its recommendation for the new configuration. (It suggests about four pounds more than what I need for warm-water diving, so I would deduct that from its suggestion for a different tank/suit as a starting point.) You look like a tall guy in your picture, and the HP100 is fairly short. A longer tank might trim out more easily for you.
     
    Last edited: Sep 25, 2016
  3. CT-Rich

    CT-Rich Solo Diver

    2,380
    2,170
    113
    I've never seen that calculator, but, surprisingly, it was with in a couple of pounds of what I have been using this year. I'm really tall, so I can't say if the numbers will be accurate for others, however, more accurate than I would have guessed.
     
  4. spectrum

    spectrum Dive Bum Wannabe ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: The Atlantic Northeast (Maine)
    11,376
    817
    113
    38 pounds of lift is more than enough so you're good there.

    The empty buoyancy properties if the AL100 and HP 100 are very close with the HP 100 being about a pound heavier depending on brand (PST, Worthington) and specific cylinder. Some Fabers can be considerably heavier. Again it is the EMPTY BUOYANCY you want to compare to get the delta.

    Going to fresh water from salt is a question of displacement. Tally up your total weight before you get in the water and divide by 40. I'm guessing you get to leave 7-8 pounds behind in fresh water.

    Those 2 were basic physics and specifications. The wetsuit is a little less tangible unless you do the work of measuring. It's a bummer that makers do not publish the initial buoyancy of suits. I know from my data that going from trunks to a 5mm wetsuit in fresh water means 10 pounds in an XL suit.

    So, the water and cylinder save you about 8 pounds of lead. The wetsuit may be an additional 12 so I'd try going in with an extra 6 (30) pounds to be safe. Make sure some of it is in 2 pound increments and someplace where you can remove them. In the shallows at the end of the dive with a depleted cylinder and empty BC bladder remove weight until you are neutral. See here.

    Pete
     
  5. RyanT

    RyanT Solo Diver

    # of Dives: 500 - 999
    Location: Maryland
    1,772
    1,416
    113
    The Faber's will definitely be heavier (about 5 lbs more negative than an AL 80 when empty).
     
  6. spectrum

    spectrum Dive Bum Wannabe ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: The Atlantic Northeast (Maine)
    11,376
    817
    113
    I assume you meant (about 5 lbs more negative than an AL 100 when empty)

    An AL80 is ~4.4 pounds positive, The PST/Worthington Steels about 1 pound negative. That is ~5 pounds more negative than an AL 80. Faber has stuff ~6 pounds heavier that the HP100's I cited that is ~6-7 pounds negative.
     
  7. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Boulder, CO
    25,635
    17,080
    113
    I just tried that weight calculator using my personal statistics from when I dived salt water using a 3mm suit, a BCD, and an AL 80. It said I needed 19 pounds. When I dived that way, I used 8 pounds, so that calculator wanted me to wear roughly 2.5 times as much weight as I actually needed. I then put in the statistics for a student with whom I recently worked using a 7mm suit in fresh water. The calculator said he needed 18 pounds. He needed 10.

    I find it very hard to believe you need 24 pounds with no wet suit. Diving in salt water with a BCD and no wet suit, I would need almost no weight at all. When I have instructed students in a fresh water pool while wearing a 3mm shorty and demonstrated a proper weight check, I have needed no weight whatsoever.
     
  8. RyanT

    RyanT Solo Diver

    # of Dives: 500 - 999
    Location: Maryland
    1,772
    1,416
    113
    Spectrum: No, I meant an 80. I'm guessing it probably depends on the brand of AL 80. The current Faber steel HP 100 is listed as -0.6 lbs empty. So lets say realistically its -1.0 with a little gas in it. An AL80 at +4.0 empty gives a difference of about 5 lbs. Of course it does depend on the brand of tanks you're comparing as they will vary a little.
     
  9. rhwestfall

    rhwestfall Solo Diver

    # of Dives: 200 - 499
    Location: "La Grande Ile"
    12,486
    11,294
    113
    IIRC, that -0.6 is w/o valve, and really a useless number IMHO.... The tank charts are such a mess... I too wish there was an "Industry Standard" way of listing them...
     
  10. noj3333

    noj3333 Solo Diver

    # of Dives: 100 - 199
    Location: Albany, New York
    862
    393
    63
    In you opinion would someone be able to 'swim up' a somewhat empty HP100, with a compressed 5mm wet suit, if my BC failed?

    I misspoke, I just checked my log and I need roughly 20-22 lbs. I am going to be doing some more tropical diving in November. These dives will include some work with Pete 'NetDoc' on trim/ buoyancy over a few days. I hope to fine tune my lead then. As a side note I went from 20 to 22 lbs when I was diving in Grenada. I started to get floaty towards then end of that dive, and the DM gave me another 2 lbs to help me stay down, so I'm somewhat confident in my numbers.
     

Share This Page