DPV BLADEFISH BF5000 SEAJET

The Bladefish is different.
I'm told that it was designed and developed in the UK, but it's obvious that it is made in the Far East.
All DPVs consist of three items: a power source, a motor and a propeller. Usually, the big battery needed takes up most of the space and accounts for most of the weight.
What makes the Bladefish different is its use of lithium-ion batteries, sealed within the unit.
These take up very little space for the amperage/hours available, so the Bladefish looks like a DPV with the big front part missing. I've seen fan-heaters that look similar.
Firstly, what are the disadvantages of lithium-ion batteries? Well, when they're finished with you have to dispose of them in compliance with local regulations. I doubt if they meet the regulations for carrying on aircraft (though who's going to tell?) and, if you get a leak, presumably from mishandling the unit, sea water can combine with li-ion to provide some interesting fireworks.
I asked Mark Bruce, the resident instructor at Wraysbury Dive Centre, to try the Bladefish in the lake one snowy morning in early February.
Well, he was wet anyway, from having just given some unfortunate an Open Water Diver lesson. I was quite pleased that I didn't have to get in. The water looked less than inviting!
I asked Mark to travel the length of the lake, and strolled up to the jetty, where I expected him to get out. Checking the progress of his bubbles, I calculated that he was doing about 3mph, which is quite quick.
When he surfaced through the icy covering, I turned to Arthur, otherwise known as "I'm Just The Cook", and said I was going to test Mark by telling him he could do a circuit of the lake if he wanted to. Mark was obviously enjoying himself, because off he went.
You drive the unit by simultaneously pressing down two switches mounted at the tops of the symmetrical handles.
Press them once, and you get the slowest speed. Letting go and pressing again quickly brings up the next speed. Press them again very quickly together, and you get the next speed.
We were expecting to get three speed settings with this model, and did at the surface, but Mark couldn't detect the full effect under the numbingly cold water. "I only found two settings, but it really took off when I got it going on full speed," he reported.
This unit is depth-rated to 50m but, unlike the TV news reporter who dived under the ice at Wraysbury in January and told the world that he went to 20m, as far as we know 7m is about as deep as you can get there. Perhaps he meant feet. Provided it doesn't flood, a DPV should work the same at any depth.
The 18V battery-pack is good for around two hours' continuous use, but we let Mark get out after 20 minutes. He was having so much fun that he might have stayed in longer.
His thumbs, alas, holding down the metal switches, went numb in the cold.

In the Water
Mark reported that the Bladefish really moves once it gets going. However, if you let go of either power switch it stops dead in its tracks, and because it has no big battery chamber to provide neutral buoyancy, at this moment it turns into a brick. It's very negatively buoyant.
The other drawback is that you really have to keep releasing and repressing to move through the speeds. All this said, when running Mark thought it was easier to control and point the Bladefish where he wanted to go than it was with some rival full-bodied DPVs.
He also said that it was quite comfortable, with no noticeable backwash. Use some DPVs incorrectly and they can wash your mask off your face.
Once you get used to it, he said, you can hold it out directly in front of you, whereas with most other DPVs it's best to position yourself horizontally over the top. The backwash effect of the Bladefish is far less intrusive.
There were no attachment points for a lanyard. Serious cave-diving DPVs are controlled with one hand while a lanyard tows the diver along. You have to hold onto the Bladefish continuously, and Mark observed that, with his heavily gloved hands, there was little space left on the handles.
I travelled the next day to the Red Sea, where I met diver Robert Land, a guest on the Contessa Mia liveaboard . He had learned to dive six years before, when he was 65, and had recently purchased a Bladefish because he felt it would give him confidence whenever he found himself swimming into a current.
He had broken the rules and attached a lanyard so that he wouldn't lose it when he wasn't using it. He told me that its negative buoyancy was not so great as to be a burden, which reflects the difference in salinity between the Red Sea and Wraysbury.
In the sea, the noise of the Bladefish working was quite obvious. It certainly scared off any turtles that might have been feeding and otherwise available for my camera. Somebody observed that he had a strimmer that was quieter. Other divers on the trip called it "Bob's damned lawnmower". I rather uncharitably called it "Bob's underwater wheelchair".
During the week, however, Bob started to have problems with the switches. It appeared that water was finding its way past O-rings, and at first one switch remained permanently making contact.
Eventually the second switch suffered the same problem, and the only way he could turn it off was gingerly to pull out the red charging plug a little way. Bob became disappointed with his purchase. It turned out to be a battery cell problem that has since been fixed.

Charging
The BF5000 takes four hours to charge fully, but is 80% charged in only two hours. The unit has some LEDs that go from flashing red to continuous green depending on the state of charge.
In use, similar LEDs gauge the duration of the battery-pack. Continuous green means that there is at least 80% charge, whereas flashing red indicates that you're on the last knockings.
You pull out a watertight plug (with two O-rings) and insert the charging lead. It's the devil's own job to get it out, because it's such a tight fit.
Leaving the watertight plug out means that the unit cannot be activated during storage, and I guess two are supplied because you're bound to lose one in a "drop, plop, expletive" scenario if you try to fit it while in a small boat.

Comparable DPVs to consider:
Seadoo Explorer, £599

SPECS
PRICE £500
WEIGHT 4.2kg
MOTOR 18V, 240W
DEPTH RATING 50m
SPEED 5.25kmph (3.26mph) (manufacturer's figure)
RUN-TIME 120min
MULTI CELL MONITORING Yes
PROTECTIVE CIRCUITRY Yes
RECHARGE CYCLES 300
CONTACT www.beaversports.co.uk
DIVER GUIDE