Neutral buoyancy is the much coveted objective in diving type activities. You don’t want to weigh too little and have to struggle to get and remain submerged, and you especially don’t want to weigh too much for equally evident reasons. Ballast is what vessels take on to keep that sweet spot above the waterline which gives boating its appeal. On the other hand, humans wear weight belts which are always preferred to concrete galoshes. In a Diver Propulsion Vehicle – DPV – neutral buoyancy is integral, as one would hope while being dragged underwater by an electrical device that weighs about 50 lbs.
DPVs like the Seabob F5 S and Sea Doo RS1 promote their crafts' neutral buoyancy and with good reason. When not struggling against negative or positive buoyancy, the run time is optimized, giving the diver more bubble for their buck. As well as not dragging diver and their expensive propulsion device into the depths of Davy Jones Locker Room.
Constructed of lightweight aluminum with a hard anodized coating, the Hollis H-160 is resistant to corrosion and abrasion -- always good qualities in a water borne device. It looks very torpedo-like with a cycloptic eye in front and a single-grip handle over the prop. The prop has a guard around its external circumference but the blade is reachable through the back, which seems kind of dangerous to those fond of their fingers. The H-160 has 3 power settings, 50%, 75% and 100%, offering a one-hour burn time at 100% with two hours at 50%. With a top speed of 2-3 mph, generating between 45 and 60 lbs of thrust, the H-160 is depth rated at 656 feet. Some users have noted the H-160 is negatively buoyant with a tendency to sink tail-down. Promotional material on the Hollis H-160 do not make note of its buoyancy ratings and offer conflicting thrust ratings. Given its price relative to the competition, it seems this information should be better defined.
You can easily use it by using only one of your hands. This means you can carry your underwater camera and/or torch.
Cave divers generally use Sealed Lead Acid batteries rather than NiMh batteries. They believe that the simple is better. Hollis H-160 has a NiMh battery.
When the scooter is not in motion it does become very negatively buoyant, but it does plane out very nicely when in motion.