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Richie · 01-27-2003, 02:46 PM,

I'm thinking about building a DPV (diver propulsion vehicle) and I am curious if anyone knows anything about building one, any online resources (websites, etc.), email addresses of anyone that's built one, or anything else that might get me cruising underwater. Lemme know! Thanks.

Richie
;D
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My favorite stupid comment (this week...):
500 psi? Why not just breathe your buddy's air?

01-27-2003, 03:48 PM,

Unless you have a very thorough background in engineering and manufacturing I would not recommend tackeling this project. There are some plans that you can buy for like $25 online, but most of those designs perform very poorly, and are only depth rated to 30ft. You can find used Tekna's for sale for about $800, which are rated to about 150ft and will run close to an hour with new batteries. That's definitely a lot cheaper than any homemade design with the same specs.
If you do have the abovementioned background, you could tackle the development of a deep tow-behind scooter a la Gavin or SS, but you'll be looking at about $2800 in parts and manufacturing.

Richie · 01-27-2003, 04:41 PM,

I understand the complexity of the project. I have a milling machine, metal lathe and a working understanding of electronics.

Here are the details so far:
My first version will be a bit bigger than I'd like seeing I'm using 12.75" HDPE with a .75" wall thickness. This can handle 100psi from the inside, so the outside crush pressure is MUCH greater. It'll easily get well below 150' which is way past anything I'll do with it. Each foot of this material will require 60+ lbs to sink it due to what it displaces. My motors are 28lb thrust trolling motors powered by a sealed 12V 35A/hr battery (20ish lbs?). The batteries are VRLA AGM (absorbed glass mat) type purchased from Batteries Plus for $75/ea. My trolling motors are from some dude on the internet for $40 + shipping & tax (I'll get you the name if you need it). I think I'll get 2 knots for 60 minutes but the later version's gonna have a 50lb motor (24V, bigger, faster, HEAVIER). From a dude I've chatted says it'll go approx 5 knots though it'll flood your face mask and your jaw will get tired from holding onto the reg...
For this version I'm gonna use the resistive speed controller that is built with the motor but I have plans on creating a pulse width modulator (using a 555 timer circuit) to alter voltage instead of using resistors (too much heat and they're wasteful on power).
The tube will be lathed to have an edge that will contain an O-ring and the caps will have the opposite lip so that they fit tightly together. Not sure about what clips I'm going to use to faster this all together. It'll be interesting this winter seeing I'm gonna have to test it in whatever open water I can find (the river??).

I guess I was only looking for thoughts, ideas, etc to help me. Never hurts to share knowledge and I welcome all opinions. If anyone's got anything to add/question, please let me know!

Richie
Tongue

01-27-2003, 04:57 PM,

Speed is not the most important factor with a DPV. The water density requires so much energy to propel the diver through the water, that what is of main importance in the design is torque. The more torque at lower RPM's the better it'll function in the water. I would not recommend using electronics to change the output speed (such as the Farallons use), but rather a mechanical variable pitch control of the prop blades - much less prone to failure and doesn't require any drilling through the hull. I would also recommend separating the battery compartment from the engine compartment - you're more lkely to flood the battery compartment through the nose cone (where you'll be charging the batteries), but at least you won't fry the engine.
I definitely recommend going with a tow behind design - it's much more efficient from straemlining point of view, and doesn't put any stress on the diver as far as the towing is concerned (as opposed to holding on).
Check out . They have some crushing depth calculations on there with using HDPE for the body.

I personally have no experience bilding these things, nor do I have a mechanical background, but I have been using these things for a while now, so I kinda know what works and what doesn't from a diver perspective.

Richie · 01-27-2003, 05:10 PM,

Funny you mention silent submersion....

This is the design that I'm attempting to copy. My batteries will all be attached to the motor as they do with a waterproof bulkhead (O-ring on outside edge of bulkhead) beside the endcap. I will change hull lengths if I need additional batteries. The nose piece doesn't even really seem necessary except it might be easier to charge without having to remove everything, depending on where my battery posts are located. Just a thought: Never charge batteries in a sealed container. Hydrogen gas is produced and can go BOOM!

The really high quality and expensive models use variable pitch props which are amazing but aren't gonna be used for mine. That might be why silent-submersion is $3600!

Richie

**freedivernd** · 01-27-2003, 08:19 PM,

Sounds like you've got a good plan Ritchie. Good luck with it. You want open water.. bring it up to the pool here.. we can test it to -10'. If it works well maybe you can build me one.

What about using threads in conjuction with the o-ring like some underwater flashlights instead of clamps for closing?

So many projects so little time... should spend 1/2 the time on my projects as I do on the mnscuba board.

Fred

01-27-2003, 10:20 PM,

Threads are a bad idea - the o-ring(s) receive a ton more abuse that way from being turned. Latches are the way to go - check out McMaster-Carr - I believe they have SS depth compensating latches - the kind you want.

Also, Richie, check out . That's the basic tow behind design to which all othr scooters are measured (although the SS did improve upon it. As far as the variable prop pitch is concerned - you should be able to get the assembly fairly cheap (in the $100 range if I'm not mistaken) from . You can talk to Kurt there, he's a great guy and I bought my Tekna from him a couple of years ago. I'm pretty sure he's also very open at answering technical questions if you have any.

Richie · 01-28-2003, 01:23 PM,

This is exactly what I'm looking for. Thanks!

What pool are we talking about? It would be great to have an indoor resource, but will they care that I'm playing around with batteries in their water?

**freedivernd** · 01-28-2003, 03:01 PM,

Ritchie,

When I said "bring it to the pool up here" I was maybe being a bit sarcastic... I'm almost 300 miles from Minneapolis. I train there (Mayville University) almost everyday and I doubt if they would mind you trying out your DPV.. as long as it was sealed. Those batteries must be sealed batteries aren't they? Not going to break under 10' of water pressure I hope.

I've heard that freediving with a DPV is great fun.. that's why my interest in the subject.

Fred

Richie · (This post was last modified: 01-28-2003, 03:12 PM by Richie.)

Okay... I wasn't sure if you were in Mpls or not... Your pool is a bit of a haul. Maybe if I'm in your area sometime.
Wait, you're not supposed to use regular car batteries?? I did protect them in food plastic wrap and taped them to the side of the hull...

I'll certainly keep everyone posted. I plan on taking pics and creating a website so that others who have an interest can get some assistance building one. Well, that is if it actually gets built... The parts are on the way but time is gettin' slim.

If anyone has other thoughts/ideas/suggestions send them to me! Happy diving.

Richie