cool_hardware52
Contributor
LOL at anywhere near 3 mph you wouldn't be able to do any of those body contortions as the drag from the scoot would pull you straight back - especially without a tow chord and harness.
I own a 3mph scooter. Verified with timed passes over a surveyor checked 1/4 mile underwater course in Lake Tahoe.
43 lbs total, 1150 watthour Li-ion battery. The motor alone = the weight of a Bladefish.
These scooters produce in excess of 75 lbs of thrust. Verified using a Bollard pull test and load cell. It then follows that the drag of a skilled diver is about 75 lbs at 3 mph.
Drag increases as a the square of the speed. To go from 3 mph to the claimed 3.75 mph requires (3.75/3) * (3.75/3) * 75 lbs or ~117 lbs.
How long could any diver hold onto, even using both hands, a scooter producing 117 lbs of thrust?
To keep things in perspective:
The typical reasonably fit human can produce ~1/10 hp continuously for moderate periods.
1 hp = 746 watts. 1/10 hp is ~75 watts. The bladefish claims to have a 210 watt motor. 210 / 75 = 2.8
If a diver is used to moving across the reef with a relatively inefficient 75 watts of swimming power and they get a hold of almost 3 times that much power with turning a propeller it will *seem* like they are flying with much less effort. Moving at 100 fpm (1.14 mph) vs 50 fpm (.57 mph) is a big jump, but it's *NOT* 3.75 mph
Drag increases as a function of velocity squared. Power increases as velocity cubed.
If my ~3 mph scooters require ~1100 watts then to reach 3.75 mph would require (3.75/3)^3 x 1100 = ~2150 watts. A motor capable of delivering 2.150 Kilowatts or almost 3 hp is going to to weigh about 20 lbs.
The Li-Ion battery necessary to drive 2.15 kilowatts for an hour will weigh ~25 lbs.
How do you get a 20 lbs motor and 25 lbs battery into a 10.5 lbs scooter?
Tobin
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