Specifications

* Maximum speed of tow will be 3.5 knots, about 355 ft/min or 108 m/min
* Maximum depth 3000 ft, 915 meters.
* Maximum cable length: 4000 ft, 1220 meters.
* Maximum cable diameter 1/4″ communication cable parried with a 3/16 synthetic
strength member bound together with a 2 inch wide fairing material
* Single speed drive.
* Electronically load sensor in order to release line and alert the pilot in the even the tow is fouled.
* DC Electric powered. Preferably 12v

Cable

4pr 24 gauge AWG 4 pair Cat 5E Direct Bury

Specialty cable for deep water ROV’s is very expensive so we are opting for using the common, inexpensive bury type Cat 5 computer network cable network with 4, 24 awg twisted pairs

We looked into making syntactic foam floats  to offset the weight of the cable but they present an issue with tangling the line, not going on a spool, and not providing consistent buoyancy over the length of the cable.

10580042_873974529281373_7479255910895023147_nA better idea was to use hollow braided polypropylene rope, which floats, and insert the cable inside the rope.

Wet weight (weight in water) of 200 ft of Cat5 direct bury network cable is .4 lbs per 200 ft. The buoyancy for 100 ft of 3/8″ hollow braid Poly (polypropylene) rope is .4 lbs per 100 ft. So 200 ft of hollow braid would provide .4 lbs of positive buoyancy to accommodate for fresh water, compression and the little air bubbles that were trapped in the brad when I did the measurement. And we can weave yarn into the brad on the last 1000 feet to help counter strumming. Breaking strength of the Cat5 is about 500 pounds and the poly is about 500 lbs, working is 220 lbs. The OD of the poly over the Cat5 is .42″ (About 7/16″) which means 2000 ft will fit on our current winch drum.

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We put gel-filled Cat 5, bury type, network cable; 13 cents/ft,  inside 3/8″ hollow braid polypropylene rope, about 10 cents/ft as it take about 120 ft of poly to cover 100 feet of Cat 5.  The result was just slightly positive buoyant even in fresh water. The working load for the 3/8″ poly is only 215 pounds but we were hoping that the Cat 5 would increase that so I sent samples to Austin Downey to test and the results are in the graph. Ignore the elongation, we just tied a knot in the sample. But the good news is that it looks like we can sustain a working load of 500 pounds and we don’t loose communication till we hit 700 pounds, and we don’t loose the ROV unless we exceed 1000 pounds. Many thanks to Austin.   Our later test generated much lower numbers on the Cat5 as it broke around 420 lbs, and I suspect that was due to testing a longer sample with less pre-tension in the hollow brained poly.

After several hours of work we had over 600 ft of gel-filled Cat5 direct burial cable inside 3/8″ polypropylene giving us a  tether that cost only 23 cents / foot, takes 700 pounds before the before the copper conductors break and 1000 pounds before it completely parts.

Hollow Braid PolypropyleneThe down side to direct burial cable is that it uses solid copper wire and not stranded copper wire.  Stranded wire survives longer with  flexing, but they don’t use it for buried cables.   We like the gel-filled bury cable because it contains no air that will compress at depth and cause the cable to become heavier.

We posted the video; Low Cost ROV Tether and more…  and got two great suggestions.

Braids and Laces in Cannington, Ontario can weave the polypropylene rope around the Cat5 cable we supply for 193 Canadian, or $152 usd, plus maybe $100 in brokerage fees + 120 shipping.  That will bring our poly rope cost from 8 to about 21 cents a foot, but save a day of work and hopefully improve the quality.  So we are on the hunt for Gel-filled, stranded Cat5.  If we can keep the Cat5 cost to 13 cents, then we end up with a great 300 pound towing tether for $340 per 1000 ft.      Cable Sales Canada has the bury Cat5 we want as well as stranded conductor Cat5 to test.   So 0.372 for the rope and braiding and .13 for the cable brings to total to just over 50 cents a foot.    We are also talking to Atwood Rope in Ohio.

Polypropylene Tubular Webbing

Polypropylene Tubular Webbing

Another wiz bang suggestion from Bob Cartwright  was to use polypropylene tubular webbing, and it is available from Shan Li Weaving .   The upside of tubular webbing is that it will be easy to insert the cable, and even replace the cable when it becomes damaged.

Tubular webbing may also be the perfect answer to “cable strumming”, a phenomenon that occurs when round cable is dragged through the water.  Uneven pressure builds on one side of the cable causing to to move to to low pressure, and that movement cause a low pressure on the opposite side, so the cable begins to vibrate.  You may have see fishing line do this just before it breaks, because the vibration greatly increased the drag.  The material  in the tube will create a laminar flow around the cable and help prevent strumming.

When cables they start strumming the drag increases, and then the cable breaks.  Video I’m hoping the tubular webbing on the ROV’s tether will act like a fairing similar to what the pros are doing: http://www.odimspectrum.com/seismic.html

100ft of poly only covers about 64 feet of 1/4″ Cat5.   And 3/8″ poly weighs approximately .288 oz per foot, or 26.79 grams per meter.  So the actual weight per foot is (100/64)*.288 = 0.45 oz or 41.86 g/m.    Weigh of 42g/m translates to:  1.5″ wide by 2.3mm thick,  1″ wide by 3.2mm, and 1.25″ wide by 2.7mm.   These are custom manufactured by shanliwebbing.com for 0.228 usd/yard, 0.076 usd/ft.   The shipping is $610 for a 3000 yard spool bringing the cost to about 15 cents a foot.  Add the cable and the total price is 27 cents a foot.  Just 4 cents more than our cable in poly rope solution and possibly stronger and with much less time required for inserting the cable.  We may also be able to easily replace a broken cable when using tubular webbing.

The Coax Option – 1+ Miles!

Coax like bury type Cat5 is widely available and hence a great value, but until I met Zach and Electrical Engineer at the Tulsa Maker Fair that told us about Ethernet Over Coax devices.    Dual shield is about 6 cents a foot, quad shield about 13 cents.

TRENDnet Mid-Band HPNA Coaxial Network Adapter (TPA-311)  196Mbps, 1600 meters, $80   Will need to be modified to fit the hull.
Seco-Larm Enforcer Ethernet Over Coax with PoE (NE-AE01-030TQ)   10Mbps @984 feet, 300 m  $165   Fits the hull.
IPC600 Octava Ethernet over coax Extender with PoE, 100Mbit, 2600 ft , 790 m,  $199
EOC1110K Gigabit Ethernet over Coaxial Unmanaged LAN Extender Kit  112Mbps @ 2,952 ft, 900 m $300      Might fit with modifications.
ebay.com from China:  IP/PoE over coax,  100Mb up to 8000 ft, 2500m $126   Fits the hull.
C4L6400-EoC-P  www.c4line.com   info@c4line.com

Another idea from Zach:  ”

Hook two RF Ethernet radios together via a COAX.  I can get 2 miles with open air with two of these so with a coax hooked to them I bet they will go much farther: http://www.wlanparts.com/ubiquiti-networks/2-4ghz-equipment/ubiquiti-picom2hp-2-4ghz-802-11n-high-power/ In fact I’d be worried about hooking them straight together directly with cable lengths shorter than 1000ft, but they are really robust they take lightening and the real world shit really well so I bet it wouldn’t hurt them.”
Common Coax in the USA is RG6 Quad shield,  gel-filled  or Aerial RG6 with a steel messenger wire are only 7 cents/foot  .  Cat5 gel-filled is 13 cents/ft.   RG6 Quad shield is only 0.18″, 4.57 mm.
Cable Breaks inside Tubular Webbing

Daniel and Rob

Daniel and Rob

The samples have arrived and Shang Li Webbing says:  “The 1″ is in thickness 2.9mm, weight 46g/m, tension strength value 934kgs. The 1.5″ is in thickness 1.9mm, weight 45g/m, tension strength value 769kgs.”     That is over 2000 pounds of strength for the 1″ and 1600 pounds for the 1.5″ wide webbing.   But we quickly found a problem with the first test.  The tubing stretches 35% with 300 pounds without gripping the cable as the braided rope does it simply allows the cable to take the bulk of the load and the RG6 cable broke.

The industry recommended load for RG6 ccs, or copper coated steel core is 75 lbs, and 35 lbs for solid copper core.  The actually breaking strength for RG6 ccs is just over 400 pounds.    Much better than Cat5 solid core that breaks around 180 lbs.  But even the stretching of coax will reduce it’s ability to carry a signal as the distance between the core and the shield are reduced.

We could add a 1/8″ Galvanized Steel Wire Rope, 7×19 Strand Core with a 0.029 lb/ft.  The additional cost of the cable would be about 8 cents and as coax is about 0.0082 lb/ft, we would need to triple the volume of the webbing in order to compensate for the weight of the steel cable, adding another 24 cents.  The total cost of the tether would then be about 60 cents a foot.   Much higher but still half that of the lowest cost neutrally buoyant tether on the market and with a towing capacity of 1000 pounds.

Dyneema rope 3mm 1000 lb, 23 cents/ft    Total cost of 50 cents / ft.  But even Dyneema stretches 2% at 50% load, or 10 feet over 500 ft. Steel 7×19 is 1.13% at 50% and 1×19 is only 0.5% but its hard to find.
So what is the best combination of polypropylene tubular webbing, coaxial cable and strength member, either steel of synthetic so that we have a low cost, neutrally buoyant, anti-strumming, tether that can sustain a 1000+ pounds of load when towing?
The Ribbon Factory makes pretty ribbons as well as polyester pull tape for dragging cable through conduits.  And their customer service is outstanding.  I asked about the stretch in their products and they ran a test and replied the next morning.  “The percentage of stretch for the 2500# @ 50% load is 16.26% plus or minus 2%.  The percentage for the 6000# @ 50% load is 25.48% plus or minus 3%.”   The 6000 pounds pull tape is only 11 cents a foot.   Unfortunately I think that is still going to be too much for the coax or Cat5 to bear.
In our test RG6 dual shield copper clad steel core stretches proportional to the load.   At 70 pounds; ( 75 is the recommended max)  it stretches only .85%.   So the plan is to coil the RG6 around the pull tape so that the RG6 can simply straight out as the tape takes the load. For 100 ft of tape we will need to wrap on about 125 ft of RG6.  A lot of wraps and a 25% increase in RG6 cost and weight and likely a 25% increase in the required poly webbing to support the extra weight.  So roughly .08 for the RG6 + .11 for the tubular webbing + .11 for the pull tape = 29 cents/ft.

3mm Dyneema at 50 cents/ft  would be much better as it only stretches 2%.  but the cost of the cable would double to 70 cents / ft.

Cat5 solid copper
Lbs Length % Stretch
0 145.500
13 145.625 0.090
35.8 146.313 0.560
56.6 147.000 1.030
77.0 149.313 2.620
Broke
RG6 dual shield, copper clad steel core
Lbs Length % Stretch
0.0 140.500
13.0 140.875 0.270
35.8 141.000 0.360
56.6 141.313 0.580
77.0 141.688 0.850
97.6 141.688 0.850
117.4 141.875 0.980
135.3 142.000 1.070
153.8 142.125 1.160
174.4 142.188 1.200
190.6 142.375 1.330
211.3 142.563 1.470
209.3 142.688 1.560
211.4 143.125 1.870
Broke
Cat5 solid copper, gel-filled, burial.
in 3/8″ hollow braid polypropylene.
Lbs % Stretch
28.9 0.3
49.2 0.7
70.3 1.4
91.0 1.9
111.4 2.5
131.4 3.0
151.9 3.4
171.4 3.9
190.9 4.6
211.5 5.1
229.8 6.0
249.4 6.6
269.3 7.4
290.1 0.0
311.3 9.7
331.1
350.5 10.3
368.7
388.0 12.2
406.9
425.6 13.1 Cat5 Broke
1400.0 Poly Broke.