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As Ben mentioned a few pages ago, a few years ago divers were overly focused on maximum speed. In technical diving, I almost get it, in terms of a long dive in a deep cave where you want to maximize the penetration distance on the available gas and minimize the decompression, but it's just an...

I posted my fresh water neutral buoyancy weight results somewhere, pore-dive, but I'll repost the slightly revised post dive numbers here. Subject to the accuracy of various scales that I used (and that you might use) I needed to weight mine for 22.0 pounds. in fresh water. This leaves it an...

No matter how sharp, the seating edge on the piston still has area, and that area is not addressed by the diameter of the piston where it passes through the high pressure piston stem o-ring. On the late MK 20 and on the Mk 25 they evolved to a rounded seating edge with significantly more area...

The battery module for the Piranha is expensive to produce when you consider the machining of the aluminum billet needed to manufacture the aluminum hull section and sealing glands to very tight tolerances. And then you have the electronics that go in it. You probably noticed the BlackTip...

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...

We dove Makos for years and I liked them well enough at the time. At 53 pounds they are heavy. The hulls are also fragile and prone to leaks, especially when hauled on and off boats. Sand will get past the first o-ring and eat at the soft plastic sealing surfaces and you'll be looking for a...

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...

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...

The Dive Xtras Piranha weighs 24.6 pounds and uses four 18 volt 5 Ah DeWalt compatible power tool batteries that are very travel friendly. You can also get a travel case for it that makes it very airline proof. The Piranha trigger is finger actuated and is fully user programmable for number...

You got off the rails in the first sentence. I know Tom, and Tom knows what he is saying. More directly, I and my wife have been cave DPV divers for years, and we have experience on a number of different scooters and we have placed the towcords at both 12 and 6 and 9 and 3 on most of them...

I make the lanyards from 7 strand 550 paracord. I prefer a solomon bar lanyard as it will not tangle on itself like a line can, and they can be made quite stiff, so that they remain extended but still flexible. The degree of stiffness and flexibility is also adjustable when you make them...

SInce it is very close to neutral in fresh water with 12 Ah batteries, it has some reserve buoyancy in salt water with the 12 Ah batteries. My experience in fresh water is that that with 12 An DeWalt batteries you can get it to within 1-2 oz of netural, and that's with a bolt snap on the...

I have noted some deviation with the Piranha when running back and forth on straight lines during speed tests, but it's constant whether the motor is running or not. That said, it's not more than about 10 degrees. While you'd need a compass card for precision navigation, in general it's good...

The lack of a compass mount on the BlackTip is no great loss. The Suunto compass doesn't work all that well as it doesn't allow for much tilt before it locks up. Kayak compasses work well, and this particular model costs (a Seattle Sports Sea Rover) costs $45 and is near neutral in fresh...

I set a BlackTip up for a customer with 12 Ah DeWalt batteries for use in fresh water. I found I had to take both the mild steel weight plate and stainless steel cover plate and screws out of the nose cone. With a small bolt snap on the nose it's still about a 1/2 oz heavy, but very close to...

Dive Xtras has had a hole under each side of the handle for years, and recently they added a second hole, so there are two on each side of the handle - between the screw and the handle.

My BlackTips arrived on January 30, so I was able to take one of them to the quarry for demos on New Year's Day. Overall I was quite impressed with the performance. Visibility was low and not ideal for speed testing so I didn't do any runs over a measured course, but it did a very good job of...

I bought a pair for my demo scooter. They worked well on New Years Day doing demo dives and I'm impressed enough to order another set. If you don't need the range of the 12 Ah DeWalt batteries, the 9 Ah Waitley batteries make sense, given that you can get a pair of them for $140, compared to...

As some others have noted, you need to keep track of your buoyancy when operating a DPV. Under power, the DPV can be incorrectly used as a crutch, using a vertical thrust vector to offset negative or positive buoyancy. There are two issues with that. Most obvious is the immediate "change"...

Locking the trigger is a good idea. When the lock is properly positioned it's only three quick spins with the finger tip - maybe 1.5 turns total - between locked and unlocked. However, I also added a piece of tubing to my tow cord to prevent the line from wrapping over the trigger. The knot...