High Powered DPV

Hi Guys,

I'm working on a prototype for a new type of DPV, not completely targeted at the Scuba crowd, but figured it may definitely be of interest to you guys.

The basic concept is a DPV that is light-weight, and strapped onto the fore-arm. It will only have a short battery life (think 15-20 minutes), but will allow for high-speed underwater travel. I have quite a bit of experience with electric motors .etc, and believe I can surpass everything that is currently on the market in terms of sheer power, and also keep it compact in size.

It will have 40nM of torque, which is approximately double that of the SeaBob Cayago F7, and theoretically should be able to get up to near 25mph underwater; in theory the user should be able to gain enough speed to leap out of the water like a dolphin does, which means ultimately I will be targeting the daredevil extreme-sports crowd.

My question is - would anybody be interested in a device like this if it were reasonably priced? (i.e. 1-2k)

Any feedback or suggestions would be much appreciated. I realise it's not completely suited to the scuba crowd, but you guys certainly seem to know a lot about DPV's, so I really appreciate any input you may have

- JC

Seen this?



It was called an Armjet. I don't think it ever made it to production in any large numbers.

Developed by someone in California if I remember right. Might be the same people doing the Jetboots currently. http://www.patriot3.com/maritime-products1/jetboots

You had me right up to the 25mph, nice troll

Definitely not a troll. 25mph may be high expectations, but the motor I'll be using is almost 40x as powerful as the one used by the Armjet, although the end product is basically the same as that in every other way.

If the Seabob can do 14kmh underwater with full scuba gear on and huge weight; it doesn't seem that unrealistic that this could achieve speeds nearing 25mph.

Realistically, only 8mph is necessary to be able to launch out of the water - very doable.

Here's a little experiment you might want to try. Tie a rope off the stern of a boat, put your gear on, now have the boat drag you at 25 mph.

Let me know how that goes.

codo3500:

Definitely not a troll. 25mph may be high expectations, but the motor I'll be using is almost 40x as powerful as the one used by the Armjet, although the end product is basically the same as that in every other way.

If the Seabob can do 14kmh underwater with full scuba gear on and huge weight; it doesn't seem that unrealistic that this could achieve speeds nearing 25mph.

Realistically, only 8mph is necessary to be able to launch out of the water - very doable.

Click to expand...

Power required goes up as the CUBE of the velocity. It requires ~2.2 hp to reach ~3 mph. 25/3 = ~ 8 8^3 = 512. 512 X 2.2 = 1126 HP

Good luck.

Tobin

1126 HP? Easily doable. You just need to buy one of those portable nano technology based nuclear plants. North Korea can help.

cool_hardware52:

Power required goes up as the CUBE of the velocity. It requires ~2.2 hp to reach ~3 mph. 25/3 = ~ 8 8^3 = 512. 512 X 2.2 = 1126 HP

Click to expand...

The math is not quite that simple, since the propeller system needs to be factored in, but since it will be mounted to a persons arms, it limits the propeller size to something rather small. A lot of power into a small prop, just becomes a cavitation generator unless back pressure is created, such as with a jet pump type of system, which is even less efficient.

A more direct "sanity check" would just be to look at the drag force, which increases with the square of the velocity and has nothing to do with power or propeller efficiency. A swimmer at 3 MPH requires about 60-80 lbs of thrust depending on the person.

25mph/3mph = 8.33 times more speed

8.33^2 = 69.4 times more force

69.4 x 80lbs thrust = 5552lbs of thrust (Not exactly, since fluid dynamics are never that simple, but you get the idea)

Fortunately, the thrusters should easily exceed 25 mph, since the drag will decrease significantly after your arms are ripped from your torso.

Sorry to burst your bubble.

Cheers,
Jon

codo3500:

It will have 40nM of torque, which is approximately double that of the SeaBob Cayago F7, and theoretically should be able to get up to near 25mph underwater; in theory the user should be able to gain enough speed to leap out of the water like a dolphin does, which means ultimately I will be targeting the daredevil extreme-sports crowd.

My question is - would anybody be interested in a device like this if it were reasonably priced? (i.e. 1-2k)

Any feedback or suggestions would be much appreciated. I realise it's not completely suited to the scuba crowd, but you guys certainly seem to know a lot about DPV's, so I really appreciate any input you may have

- JC

Click to expand...

Codo, Im not an engineer so I can't comment on the feasibility of designing a 25mph dpv.

I am not yet DPV certified (going to be in July) but my main concern would be safety. I feel at those speeds, a rapid change in profile would be all too easy and hazardous if you are on SCUBA.

That being said, I dont want to "troll" you on the design aspects of it. One of my favorite quotes: "It's fun to do the impossible." - Walt Disney
People have always said "it can't be done," until someone comes around and does it! I'm a big supporter of following your dreams and your passions, thats why I dive! I hope the other comments ignite a drive saying "they say it cant be done so I'll prove them wrong!" rather than letting the feedback get you down. If you want to design it, go for it and make a bunch of money!! Just keep safety in mind when drawing your blueprints . Cheers man, good luck!

Jon Nellis:

The math is not quite that simple,

Click to expand...

Jon, do you disagree that power increases as cube of the velocity? If not then the math is pretty simple...........

I tend to start with simple examples when attempting to educate the profoundly ignorant.

Please note I used "~" no less than three times in my simple example to indicate that these were only approximate values.

Tobin