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Is your housing too heavy? Not anymore...


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#1 segal3

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Posted 29 June 2005 - 03:56 PM

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Imagine my 20D housing there mounted on the rail (it's in to Ikelite right now for some...modifications :) more on that later) and you'll have an idea of the full setup.

In salt water, when using the 10-22mm lens with the regular 6" Ikelite dome, the setup is completely neutral (or at least so imperceptibly negative that it would take more than a few seconds to start descending). When using the 100mm macro, the setup is just slightly negative, but nothing like it is without the core-cell foam added on. A good friend's calculations showed this to be nearly 1lb 5oz of positive lift.

Attachment of the core-cell to the ULCS arms is easy - I simply drilled two holes in each block (there are three 6"x1"x1/2" sections on each side of each arm), and then ran zip cords through the assembly, using the end of a cutoff zip cord to tighten the blocks against the arm.

More drag, you ask? Well, some of you know I've been majoring in Aerospace Engineering, and this is something I've been meaning to scan for the board for awhile:

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Notice that the airfoil...with it's *much* greater thickness, and length, has the drag of that small diameter wire. Look at it a different, and much more striking way. That tiny wire, as small as it is, has all the drag of that huge airfoil shape (note that the Wright Flyer is shown here because it was astonishing that a plane with such a huge number of wire wing supports, and the drag attached to each of those wires, was able to make it off the ground).

Drag is a force that delays or slows the forward movement of an object through a fluid when the flow direction is opposite to the direction of motion of the object. It is the friction of the fluid as it meets and passes over and about an object and its components. The more surface area exposed to rushing fluid, the greater the drag. An object's streamlined shape helps it pass through the fluid more easily. It's caused by the resistance of the fluid to move. Water is a fluid and it has mass and inertia.

This issue of drag is not just limited to the air, but also underwater. As a result, if the foam is lined up with the arm itself (and the cross-section is not presented to the flow of water), the drag is practically no different from the strobe arm alone. I used this setup in the Solomons, and did not notice any additional problems, even in some significant current. If anything, the setup was easier to use because of the reduced weight.

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The best solution would be to form-sand 'fronts' and 'backs' of core-cell to glue onto the attached pieces of core-cell to form a foil. This would yield less drag (with all core-cell attached) than the strobe arms alone...another project to work on...

Hope this has been educational :)

~Matt Segal
Matt Segal - carbonos scuba

#2 anthp

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Posted 29 June 2005 - 05:01 PM

Interesting Matt - thanks for the refresher.

I guess the only thing is that you have to make sure the camera is always pointed directly into the current, otherwise you have a sail instead of a wing and that's a whole different game.
Anthony Plummer
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"It's much better down there... It's a better place..." Enzo, Le Grand Bleu.

#3 segal3

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Posted 29 June 2005 - 05:07 PM

I guess the only thing is that you have to make sure the camera is always pointed directly into the current, otherwise you have a sail instead of a wing and that's a whole different game.

<{POST_SNAPBACK}>


Not necessarily the camera, but the arms/corecell with the least cross-sectional area...the housing is already creating so much obstructional drag that the floats are simply filling in more of that dead space if there is a sideways current...

~Matt Segal
Matt Segal - carbonos scuba

#4 anthp

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Posted 29 June 2005 - 05:32 PM

Fair call.

BTW, where did you get the foam?
Anthony Plummer
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"It's much better down there... It's a better place..." Enzo, Le Grand Bleu.

#5 laz217

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Posted 29 June 2005 - 06:41 PM

Matt,

I'd be careful about diving at the Duane in the Florida Keys with some hydrofoil wings attached to your camera. There's enough current at this wreck that you're likely to end up in Bermuda just like the Spray AUV did.

I like your concept, though. My Subal is negative with both the macro and the 8" dome setup. I could sure use a little lift. Maybe one of those Formula 1 spoilers might do the trick?!?! :)
Lazaro Ruda
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#6 UWphotoNewbie

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Posted 30 June 2005 - 10:25 AM

Matt,

I'm also an aerospace engineer so I like your thinking :)

I think a better solution would be to sand the core cell floats into the shape of an airfoil and drill them out to slip over your arm segments. If you make them loose enough that they can spin on the axis they will always point into the current like a windmill. The arm clamps will keep them from sliding up/off.

But for this to work right you would want to have more tubular arm segments like the Ikelite ball arms or the ultralight bouyancy arms I use.

UWPhotoNewbie: Not such a newbie to diving and UW photography.

Nikon D70: 60 mm, 11-16mm, 105mm, 15mm, 10.5mm

Ikelite iTTL Housing, dual Ikelite DS125

Nikon D600 topside 14-24, 28-300, 70-200, 35,50,85


#7 james

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Posted 30 June 2005 - 10:25 AM

Looks like a winner Matt. For mine, I decided to use 4 pound density closed cell Last-a-Foam.

Wait till you guys see the macro port buoyancy module I made out of 4# last-a-foam. It's faired and clamps around the macro port. 1 square foot provides SIXTY pounds of lift. Coating and abrasion protection is provided by polyesther surfboard finish.

Can't post the photos yet as I'm in Ohio and it hasn't been painted.

Cheers
James
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#8 larrym

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Posted 30 June 2005 - 05:53 PM

Good Idea! I also had an Ike housing with the ULCS arms. If anyone has been to Toys R Us or has kids, you can pick up those long styrofoam "noodles" they play in the pool with. They have a 1" hole in the center. Cut them to the length of one of your arms between the clamps, and the arm section slides right in the hole. You can add them to one or both sides of the camera if you need balance. As you go deeper they compress a bit, and seem to automatically keep the buoyancy neutral. Worked for me!

Larry