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Dive Xtras BlackTip in a cave

Discussion in 'Dive Propulsion Vehicles' started by DA Aquamaster, Jan 21, 2020.

  1. DA Aquamaster

    DA Aquamaster Directional Toast ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: NC
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    I did two dives the other day at Ginnie Springs with the BlackTip using 9 Ah batteries.

    Dive one consisted of speed runs up and down the hill 400 tunnel over a 600 ft section of line in various gears.

    I was in my side mount CCR cave configuration (KISS Sidekick, 2L O2, 3L diluent, LP85 bailout, helmet, lights and reels). Maximum power (speed 8) produced 214 fpm, while speed 4 gave 150 fpm. I ran it until it died testing it was various speeds over a 600 ft section of line out of the flow on the Hill 400 line and then swam it out about 500 ft.

    I got got the following results (averaging the run times and at each speed and rounding to the nearest 5 fpm):

    Speed 8 = 215 fpm
    Speed 7 = 195 fpm
    Speed 6 = 180 fpm
    Speed 5 = 165 fpm
    Speed 4 = 150 fpm
    Speed 3 = 133 fpm
    Speed 2 = 100 fpm
    Speed 1 = 75 fpm

    I noted it shifted down on one of the repeated speed 8 runs, due to it reaching its temperature limit. This is by design at speeds 7 and 8. However I also noted it shifted down in speed 6 half way through the following run. Water temp was 72 degrees so, in warm water at least, you do want to use speed 8 conservatively or shift down to a cruise speed of 3, 4 or 5 afterwards.

    Dive two was mostly seeing what I got for burn time at speed 4 (150 fpm), with speed 6 (180 fpm) for about 3 minutes and speed 8 for 1 minute to cover some higher flow areas of the cave. In this case it was speed 6 up and down the gallery a couple times and speed 8 through the Lips. Speed 4 was sufficient to get in the ear, and speed 6 was sufficient for the Lips but 8 made it much faster. I ran to and then up and down the hill 400 line, back and forth through the bone room and big room, and then up the mainline from the maple leaf, then back out. I still needed to run it 7 minutes in the basin before it finally downshifted, indicating low voltage from the battery.

    In short, I got a solid 60 minutes at 150 fpm (9000 ft through the water) before the voltage dropped enough to cause the scooter to shift down a gear.

    On both dives that downshift occurred with the batteries indicating 20% remaining charge when removed after the dive. The battery indicator on the BlackTip indicated 1 bar remaining.

    The advantage of power tool batteries is the ability to swap batteries between dives. At about $170 per pair, the 9 Ah Waitley batteries allow you to buy 2 sets for less than a single pair of Dewalt 12 Ah batteries. Recharge time on the batteries from the low voltage state to full charge was right at 3 hours using DeWalt DCB102 dual bay chargers.

    I had it weighted to be neutral on dive one but removed a few ounces to get it slightly positive at the surface for dive 2. The o-rings on each end of the tube compress a bit at depth and I found having it a couple ounces positive at depth improved its manners when placing a jump line as it floats up slightly and keeps the tail from contacting the bottom when the tail drops, as it trims nose up.

    (I’d like to see Dive Xtras add a 1/2” or so to the tube, or offer a longer tube option, to allow it to be a couple ounces positive with the 12 Ah batteries in fresh water.)

    ——

    Based on dive 2, I’d be comfortable scootering back 3500 ft on a BlackTip with 9 Ah batteries running at 150 fpm as you’d have about 2000’ in reserve. With 12 Ah batteries 4500 ft would be reasonable. If you want to go faster in a cave you’ll want a scooter with Piranha P1 level performance and if you want to go faster and farther you’ll want a scooter with Piranha P2 level performance.

    The BlackTip also doesn't have the refinement of the Piranha in terms of a user programmable speed control, and trims tail low rather than level. It's also only rated to 300' rather than 600' (although the crush depth is 600' so going below the rated depth by a reasonable amount isn't an issue).

    But it's also only $1500 rather than $5000. The short length doesn't make the trail low trim a big issue, if you weight it slightly positive so that it rotates nose up when you release it rather than rotating tail down and potentially contacting the floor. If you are using 12 Ah batteries you'll have more issues, but hopefully Dive Xtras will either increase the tube length slightly in the future. Alternatively, an optional short extension to accommodate the heavier 12 Ah DeWalt batteries in fresh water would be great. It would also allow for heavier batteries in the future. The BlackTip tube has the internal volume to accommodate future larger formats, but not the reserve buoyancy to accommodate heavier batteries. (An extension would however need to be an inch or two longer to accommodate the greater weight of an extension rather than another 1/2" of tube in the middle of the tube section.)

    ---

    In summary, if you want to scooter back 3000 ft to 4000 ft, swim a bit, then scooter back out, or if you want a back up scooter to get you out if your primary scooter fails 6000 ft to 8000 ft back in a cave, the BlackTip is a capable and very cost effective choice at $1500.

    Karst Scuba

    82804468_703189156876803_346759269883838464_n.jpg
     
    Dark Wolf, rng, tmassey and 1 other person like this.
  2. tbone1004

    tbone1004 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: I'm a Fish!
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    great writeup @DA Aquamaster
    any chance you can talk with @ben.mcgeever and see if you can get the hull extended enough for it to trim flat? Was talking with some buddies this weekend and while the nose up trim is pretty irrelevant while diving it, it means it is pretty useless as a tow-scooter for cave diving. If it was flat, it would ruin the market from Silent Submersion for UV's and Vipers that we're using as backup tow scooters
     
  3. rng

    rng Angel Fish

    # of Dives: 100 - 199
    Location: Richmond Hill, Canada
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  4. DA Aquamaster

    DA Aquamaster Directional Toast ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: NC
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    Based on weights and moments and the center of gravity and a wild ass guestimate of the center buoyancy I suspect a 6" to 8" longer tube would get it to a point you could get level trim, but increase the total weight to around 29-32 pounds.

    But I think you are correct, a 6" or 8" increase in length would not be objectionable in a BlackTip used as a tow scooter if it would trim level in the water, and it would be a very viable alternative to a used DPV for back up purposes.

    Ben posts here so I'm assuming he'll read the suggestion.

    If I had access to a larger lathe, I'd be tempted to turn an 8" extension and see how it works when placed behind the main tube. It would add buoyancy and move the batteries and nose weights forward, with just an extension for the battery connection and a longer strap needed to install it.

    -----

    Aside from that, it's a bit odd and less than ideal if it hits something, but you can clip the tail to a butt D-ring and tow it backwards. The tail then rests on you, and the nose stays level behind you.
     
  5. tbone1004

    tbone1004 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: I'm a Fish!
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    @DA Aquamaster towing backwards would spread your legs too wide. 6-8" puts it around the same length as UV18/Viper/Magnus and I assume the P2, so the extra length would be a nonissue
     
  6. DA Aquamaster

    DA Aquamaster Directional Toast ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: NC
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    The most practical solution I found was to clip it off like a stage bottle, but that of course increases your profile and takes up real estate that could be used to carry a stage bottle.

    If I had to carry it as a spare in my CCR sidemount configuration, I'd probably top mount it on rebreather side. It would increase the vertical profile a bit, but it would be out of the way and would not interfere with carrying two bottom mounted stages, or interfere with line handling.

    Still, if Dive Xtras can extend the tube and get it to trim level, it would be an awesome tow behind back up scooter.
     
  7. Scuba Cobra

    Scuba Cobra Barracuda

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    I had mentioned this on another thread and was snarkily told to get a piranha.
     
  8. stuartv

    stuartv Seeking the Light

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    This is probably going to sound super ignorant and maybe even stupid, too. But, if you've seen me around you probably know that hasn't stopped me before... :wink: I've never used a scooter before, so I'm very much trying to learn.

    What about attaching some kind of float to the tail of the BlackTip? Like, maybe one of those carbon float arms that you see for camera rigs? Attached to one (or more) of the shroud supports?

    Could you get it to trim level that way? Do those floats give enough lift? Is that just dumb for some other reason?

    What if they were only attached to trim it out when you're towing it, but you could take them off if you actually start to use the scooter?
     
  9. tbone1004

    tbone1004 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: I'm a Fish!
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    it would work, but you'd want to leave it on while using the scooter. Would be more ideal if they just made it a couple of inches longer to trim flat as is. Nellis actually uses a positively buoyant shroud on the Genesis scooters and I think Bonex does on their as well. Dive Xtras is still using the old style Tekna/Mako shrouds so without doing a complete redesign of the shroud, the best way to get it to trim flat is to lengthen it.
     
    stuartv likes this.
  10. stuartv

    stuartv Seeking the Light

    # of Dives: 200 - 499
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    Cool.

    I don't know how much lift would be needed. They have different sizes. They aren't cheap. They do have a lifetime warranty, though.

    But, just as example, this one gives 670g of lift. That's basically 1.5#. It's $150.

    Nauticam 70x300mm Carbon Fiber Aluminum Float Arm (Buoyancy 670g, Lifetime Warranty)

    I suspect the BlackTip does not need anything near 1.5# of lift to trim out the tail. Ones that are smaller are less money. They have them that are skinnier (so, more streamlined) also.

    Maybe 1 or 2 affixed to the very aft end of the scooter body?

    Or, really, I reckon you could fab up the same thing out of PVC once you knew exactly how much lift you wanted. One piece of tubing and 2 end caps cemented on...
     

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