New high tech float arms

Just got back from Sipidan. Used my new high tech arms. Worked great. Used with a D2X in a Subal housing and 2 DS125 strobes. This rig was well balanced before but worked like a charm in this rig. Especially considering I have chronic tendinitis in my hands.

I used silicon aquarium sealant instead of the PVC weld stuff recommended by others. This way you can twist the end off to show security if they think you are trying to smuggle a pipe bomb.

My thanks to Neal who occasionally posts on this board for giving me the idea. These prompted a lot of envy from people on Sipidan with big heavy rigs. And several unsuccessful efforts to improvise similar floats. Suffice it to say that foam or neoprene compress at depth and won't work very well.

Hey Dave, what a great idea.

Dave,

Interesting to see this. I tried something very much this a few years, pvc pipe sections with end pieces plastic tied to my ULCS arm sections, plus another long section below the tray.

I didn't think I got enough buoyancy from the pipe (I think what I used was about the same diameter as yours) to make the exercise worthwhile. With a big Subal domeport, the overall negative buoyancy isn't that bad, much less than it was with smaller dome, and it is much less if the dome is out on a 50 mm extension ring. There was a small reduction in negative buoyancy, but the increase in drag with pvc tubes on the arm sections seemed to cancel out whatever benefit that brought, at least to me.

The housing is more negative with the narrower 60 mm macro port, but the very short arms for macro aren't long enough to be worth attaching anything to.

Have you tried to quantify the buoyancy of the pvc sections and the difference they make to the overall negative buoyancy of your rig?

Sorry, I haven't done any qualitative tests on the buoyancy. As you noted the Subal D2X housing is well balanced without the float arms. I do notice the weight during a dive though. As mentioned I have tendinitis in my hands and notice the weight after awhile. With the buoyancy arms I don't have this problem. The housing felt light throughout the trip.

That is a simple and elegant solution! Dave, what size diamater PVC is that? Looks like 1.5 inch or so...

M.

Hi Dave,

Where are your Sipadan pics?

Between dealing with Jet lag, work lag, and a very large number of images it may take awhile. I bought Aperture to help me. Good program though I'm still learning it. Didn't shoot half as much as I thought and so far no great images; but I'm trying.

I echo Joe - C'mon Dave! It's very nice to see high-tech arms and all that, but I wanna see turltles!!! or anything else you'd like to show (other than arms that is).

Well, I have a few Turtle photos.

Awesome Dave - thanks for giving us a teaser!

Rather than externally mounted PCV capped tubes, why not try the closed cell foam insulation that we use for copper plumbing tubing? Armaflex and Armacell come to mind. They make two different wall thicknesses. Just make sure it is closed cell!

The insulating tubing comes with an inside dimension of 1/2", 3/4" and 1"....it is split linearly and had self adhesive tape between the split halves. Just cut it ever so slightly too long, and it will linearly compress to hold it in place, or use ziplocks at each end.

Placed it over the actual arms....then peel the tape and push the halves together......will keep your arms anodizing from getting scratched too.

Wish I knew the exact dimensions of the pvc tubes......it would be rather simple to calculate the lift created.

To find Volume of the tube, the formula is:

V=Length of tube times Pi times Radius squared

For example, if one of the tubes including the end caps measured 8 inches long and was 2 inches wide, the volume would be approximately:

V=L*Pi*r2

V = 8*3.14*1 (1 is the radius of a 2 inch tube)

V = 25.12 cubic inches

( I am aware that the end caps on the pvc pipes are slightly larger than the actual diameter of the tube itself, which is why I say "approximately")

Since salt water weighs about .037 ounces per cubic inch*, the potential lift generated would be about 15 ounces per 8 in long section. But you would still have to subtract the dry weight of the pvc tube including end caps for each section to determine the actual net benefit. iow, say the tube itself weighed out at 8 ounces. Then you would have to subtract 8 oz from 15 oz to get the actual lift.

*cubic foot of salt water = @ 64 pounds divided by 1728 = @ .037

hth,

b

Inside diameter is 1". The small tubes are 7" long and the large are 11". We tried some foam and it didn't work as it compressed with depth. Does the foam you are suggesting not compress with depth?

Dave,

Core Cell will not compress at the depths we dive. It is ultra light. My rig went from 4 pounds negative to around 13 ounces negative with very little added dry weight.

The outside diameter of the PVC tubes is what is important in the displacement calculations.

To achieve buoyancy the goal is to displace water with something that weighs less than the water it is displacing. If you displace one cubic inch of salt water, you create .037 ounces of lift. If the O.D. of your 1" I.D. pipe is 1.5" (radius would equal .75"), then the calculations for the 11" pipe would be as follows:

Volume=Length*Pi*radius squared

V=11*3.14*0.75*0.75

V=19.4 cubic inches

19.4 times 0.037 equals .72 pounds of lift (just over 11 ounces of lift)...........but you still have to subtract the actual weight of the 11" PVC pipe including those end caps to arrive at the actual buoyancy benefit........

hth,

b

I must say the PVC pipe buoyancy arms is brilliant. It is not as pretty as some other versions, but the simplicity, ruggedness, and ease of construction make up for it in my mind. Unlike all of the other buoyancy arms, this one you can put together in 5 minutes for $5.

Core Cell will not compress at the depths we dive. It is ultra light. My rig went from 4 pounds negative to around 13 ounces negative with very little added dry weight.

<{POST_SNAPBACK}>

Bob - your rig looks excellent. Where do you get that stuff you have made and how did you stick it together. Does the core cell foam have a brand name or something?

Thanks.

I used the thin PVC piping. about 2 mm thick. It is good to 128 ft at least.

Where would you get this foam?

Anthony,

Core Cell is the brand name of the closed cell foam product that I used. Divinycell is another brand name. For more info on Core Cell:

http://www.atc-chem.com/Core_Cell/Core_Overview.asp

I believe the Core Cell I used was either Core Cell "A" or Core Cell "S".

I acquired my Core Cell from a shipyard. It was excess scrap from a 51' sail boat that they were building. They were using the Core Cell to construct the bulkheads and most likely other parts of the yacht.

I used Devcon 2-ton epoxy to adhere the parts together. I used a belt sander (very carefully!) to fine tune the shapes after cutting the Core Cell with a mat knife.

Core Cell is also used to construct those deep diving mini robotic subs.

If you'd like to read more about Core Cell:

http://www.yachtsurvey.com/ATC_Core-Cell.htm

hth,

b

That's great information Bob!

I'll look into it and try to make something as beautiful as your rig.

Thanks heaps.