Seastead Tensegrity Cable System Design Analysis

1. System Overview and Loading Analysis

1.1 Structural Configuration

Living area: 40 ft × 16 ft
Leg/float columns: 4 units, 4 ft diameter, 24 ft long, at 45° angle
Submerged length per float: 12 ft (half submerged)
Footprint at water level: Approximately 50 ft × 74 ft
Total displacement weight: ~36,000 lbs (16,330 kg)
Float material: Duplex stainless steel (1/4" sides, 1/2" dished ends)
Internal pressure: 10 psi

1.2 Buoyancy Force Calculation

Per Float Buoyancy:
Float diameter: 4 ft (1.22 m)
Submerged length: 12 ft (3.66 m)
Submerged volume: π × (2 ft)² × 12 ft = 150.8 ft³ (4.27 m³)
Buoyancy force per float: 150.8 ft³ × 64 lb/ft³ (seawater) = 9,651 lbs

Total buoyancy (4 floats): 38,604 lbs
Net buoyancy (after 36,000 lb weight): 2,604 lbs reserve

Per Float Net Lift: ~9,000 lbs (accounting for float self-weight)

1.3 Static Cable Loading

Force Resolution at 45° Angle:
Vertical buoyancy force per float: ~9,000 lbs

At 45° leg angle:
- Axial compression in leg: 9,000 / sin(45°) = 12,728 lbs
- Horizontal outward force: 9,000 / tan(45°) = 9,000 lbs

Each float has 2 cables to adjacent corners (plus 1 perimeter cable)
Cable angle to horizontal: approximately 30-35° (depending on geometry)

Per cable static tension: ~5,500 - 6,500 lbs

PLAN VIEW - Cable Configuration Float 1 ●━━━━━━━━━━━━━━━━━━━━━━━━━━━● Float 2 ┃╲ ╱┃ ┃ ╲ Living Area ╱ ┃ ┃ ╲ 40' × 16' ╱ ┃ ┃ ╲ ╱ ┃ ┃ ╲ ╱ ┃ ┃ ╲ ╱ ┃ ┃ ╲╱ ┃ ┃ ╱╲ ┃ ┃ ╱ ╲ ┃ ┃ ╱ ╲ ┃ ┃ ╱ ╲ ┃ ┃ ╱ ╲ ┃ ┃ ╱ ╲ ┃ ┃╱ ╲┃ Float 4 ●━━━━━━━━━━━━━━━━━━━━━━━━━━━● Float 3 ━━━ Perimeter cables (redundancy) ╲╱ Diagonal cross cables to platform

2. Caribbean Wave Analysis and Slack Cable Risk

2.1 Typical Caribbean Sea Conditions (Non-Hurricane)

Condition	Significant Wave Height (Hs)	Peak Period (Tp)	Wavelength
Calm	0.5 - 1.0 m (1.6 - 3.3 ft)	5 - 7 sec	40 - 75 m
Moderate Trade Wind Seas	1.0 - 2.0 m (3.3 - 6.6 ft)	6 - 9 sec	55 - 125 m
Strong Trade Winds	2.0 - 3.0 m (6.6 - 10 ft)	8 - 11 sec	100 - 190 m
Tropical Wave/Cold Front	3.0 - 4.0 m (10 - 13 ft)	10 - 13 sec	155 - 265 m
Severe (Pre-Hurricane)	4.0 - 6.0 m (13 - 20 ft)	12 - 15 sec	225 - 350 m

2.2 Critical Wavelength Analysis

Diagonal footprint of seastead:
√(50² + 74²) = 89.3 ft = 27.2 m

Most dangerous wavelength: When wavelength ≈ diagonal footprint
This occurs at approximately λ = 27 m, corresponding to period T ≈ 4.2 seconds

Analysis:
- Waves with λ ≈ 27 m are short-period wind waves
- These typically have heights of 1-2 m maximum in Caribbean
- Larger waves (3-4 m) have wavelengths of 100-200 m
- At λ = 150 m, the diagonal span is only 18% of wavelength
- All floats experience nearly simultaneous lift/drop

2.3 Slack Cable Risk Assessment

Critical Finding: Diagonal Wave Attack
The worst case is indeed diagonal wave approach where wavelength approximately equals the diagonal span (27 m). However, Caribbean waves at this wavelength rarely exceed 2 m height.

Dynamic Load Estimation (Diagonal Attack, 2m wave, 4.2s period):

Wave orbital velocity: Uo = πH/T = π × 2 / 4.2 = 1.5 m/s
Wave acceleration: ao = 2π²H/T² = 2.24 m/s²

When diagonal floats are at wave crest, opposite floats at trough:
- Maximum differential vertical force: ~3,500 lbs per float
- This is less than static tension (5,500-6,500 lbs)

Conclusion: Cables remain in tension for 2m diagonal waves

Slack Cable Threshold Calculation:

For cable to go slack, dynamic unloading must exceed static pretension
Static pretension per cable: ~6,000 lbs

Required wave parameters to cause slack (diagonal attack):
- Wave height: >4.5 m (14.8 ft) at period 5-6 seconds
- Or wave height: >6 m (19.7 ft) at period 8-10 seconds

These conditions are tropical storm/hurricane conditions, NOT normal Caribbean weather

Good News: Normal Caribbean waves (up to 3-4 m) will NOT cause cable slack in your design due to:

Substantial static pretension from buoyancy
Wavelengths longer than platform diagonal for larger waves
Synchronized float motion in long-period swells

3. Spring/Compensator Analysis

3.1 Option Comparison

Criteria	Elastomeric Compensator	Nylon Rope Section	Metal Marine Spring
Elongation Range	100-300%	15-25%	10-30% (design dependent)
Fatigue Life	Good (1-5 years typical)	Fair (UV/chafe issues)	Excellent (10+ years)
UV Resistance	Fair (needs protection)	Fair (degradation over time)	Excellent
Inspection Ease	Good (visual cracks)	Fair (internal damage hidden)	Excellent (measurable)
Load Monitoring	Good (measure extension)	Fair	Excellent (precise)
Temperature Sensitivity	Moderate	Low	Very Low
Maintenance	Replace every 3-5 years	Replace every 2-3 years	Inspect annually, replace 10+ years
Cost (Initial)	Moderate ($500-1,500)	Low ($200-500)	High ($2,000-5,000)
Cost (10-year)	Moderate	Moderate-High	Moderate
Damping	High (hysteresis)	Moderate	Low (may need added)

3.2 Detailed Analysis of Each Option

Option 1: Elastomeric Mooring Compensator

Recommended Product Type: Rubber Snubber / Mooring Compensator

Specifications for 6,000 lb working load:

Working Load Limit (WLL): 8,000 lbs
Breaking strength: 24,000 lbs minimum
Elongation at WLL: 50-100%
Working length: 12-18 inches compressed
Material: Natural rubber or EPDM core with polyester jacket
End fittings: 316 stainless steel or duplex thimbles

Example Products: Unimer Mooring Compensator, Dock Edge Snubber
Estimated Cost: $800-1,200 each, 8 required = $6,400-9,600

Option 2: Nylon Rope Section

Recommended Configuration:

Type: Double-braid nylon (3-strand also acceptable)
Diameter: 1-1/4" (32mm)
Working load: 8,000 lbs
Breaking strength: 40,000 lbs
Length: 6-10 ft (provides 1-2 ft elongation at design load)
Stretch at 20% of breaking: ~15%

Advantages: Low cost, readily available, field-replaceable
Disadvantages: UV degradation, chafe risk, water absorption affects properties
Estimated Cost: $15-25/ft, ~$150-250 per cable, 8 required = $1,200-2,000

Option 3: Metal Marine Spring

Recommended Configuration: Custom helical tension spring or disc spring stack

Helical Spring Specifications:

Material: 17-7 PH stainless steel or Inconel 718
Design load: 6,000 lbs
Maximum load: 12,000 lbs
Free length: 18 inches
Loaded length at design load: 14 inches
Spring rate: ~1,500 lbs/inch
Wire diameter: 0.625" (5/8")
Outer diameter: 4-5 inches
Active coils: 8-10

Alternative: Disc Spring (Belleville Washer) Stack

Material: 17-7 PH stainless steel
Individual disc: 4" OD × 2" ID × 0.25" thick
Stack configuration: Series arrangement of 6-8 discs
Provides ~1" deflection at design load

Estimated Cost: $2,500-4,000 each custom, 8 required = $20,000-32,000

3.3 Recommendation

Primary Recommendation: Hybrid System

Given your requirements for monitoring, inspection access, and above-water mounting, I recommend:

Metal Marine Spring (Helical) + Position Sensor

Rationale:

Consistent spring rate enables accurate load calculation from position measurement
Longest service life reduces maintenance burden
Most predictable behavior for engineering analysis
Above-water location per your preference extends life further
Simple linear position sensor can continuously monitor tension

Budget Alternative: Elastomeric compensator with position marking for visual load monitoring. Replace every 3-5 years as preventive maintenance.

4. Cable Sizing

4.1 Load Analysis Summary

Design Loads:
Static load per cable: 6,000 lbs
Dynamic factor (3-4m waves): 1.5
Maximum operating load: 9,000 lbs

Design Safety Factors:
- Minimum breaking load / Working load: 5:1 (offshore standard)
- Required breaking strength: 45,000 lbs minimum

Fatigue Considerations:
- Add 20% for fatigue derating
- Design breaking strength: 54,000 lbs

4.2 Duplex Stainless Steel Wire Rope Specifications

Parameter	Specification
Material	Duplex 2205 or Super Duplex 2507
Construction	6×19 or 6×36 Warrington Seale (flexibility for bending)
Core	Independent Wire Rope Core (IWRC) - same material
Diameter	5/8" (16mm)
Minimum Breaking Load	~55,000 lbs (Duplex 2205, 6×19 IWRC)
Working Load Limit (5:1)	11,000 lbs
Weight	~0.84 lbs/ft
Minimum sheave diameter	18× rope diameter = 11.25" (not typically applicable here)

Cable Specification:

Diameter: 5/8" (16mm) duplex stainless steel wire rope
Construction: 6×36 Warrington Seale, IWRC
Material: Duplex 2205 minimum, Super Duplex 2507 preferred
Breaking Strength: 55,000+ lbs
End Fittings: Swaged terminals or spelter sockets (both ends)
Length (perimeter cables): ~50 ft and ~74 ft with adjustment
Length (diagonal cables): ~30-35 ft each

4.3 End Fitting Recommendations

Primary Termination: Swaged Fork or Eye Terminals

Material: Duplex 2205 or 316L stainless (galvanic compatible)
Efficiency: 95% of rope breaking strength
Style: Open spelter socket for adjustability, or closed swage for permanence

At Platform End (with spring):

Swaged eye terminal → Shackle → Spring → Adjustable turnbuckle → Platform pad eye

At Float End:

Swaged fork or eye terminal → Shackle → Float pad eye

5. Spring Specifications (Final Recommendation)

Recommended Spring System: Custom Helical Tension Spring

Mechanical Specifications:

Parameter	Value
Material	17-7 PH Stainless Steel (Condition CH900) or Elgiloy
Wire Diameter	0.625" (15.9mm)
Outer Coil Diameter	4.5" (114mm)
Free Length (no load)	18" (457mm)
Active Coils	10
Spring Rate	1,200 lbs/inch (210 N/mm)
Preload Position	13" (5" extension from free length)
Preload Force	6,000 lbs
Maximum Extension	10" (spring length = 28")
Maximum Load	12,000 lbs
Available Travel (tension reduction)	5" before slack
End Configuration	Machine hooks or threaded end plugs

Monitoring System:

Linear position sensor (draw wire encoder)
Range: 12" travel
Output: 4-20mA or 0-10V to monitoring system
Visual indicator: Reference marks at 4", 5", 6" extension
Alarm thresholds: <3" (overload) or >7" (low tension)

5.1 Spring Travel and Load Relationship

Operating Points:
Extension 0" (free): 0 lbs (cable slack - ALARM)
Extension 3": 3,600 lbs (low tension warning)
Extension 5": 6,000 lbs (NORMAL OPERATING POINT)
Extension 7": 8,400 lbs (elevated tension)
Extension 10": 12,000 lbs (maximum design load)

For wave-induced motion:
±2,000 lb dynamic load = ±1.67" spring movement
Normal operating range: 3.3" to 6.7" extension

6. Maximum Wave Capability

6.1 Design Capacity Analysis

With Recommended System (5/8" cable + spring compensators):

Cable breaking strength: 55,000 lbs
Maximum spring load: 12,000 lbs
Safety factor at max spring: 55,000/12,000 = 4.6:1

Dynamic capacity above static:
Static pretension: 6,000 lbs
Available capacity for dynamics: 6,000 lbs (100% increase)
Spring travel available: 5" for load increase, 5" for load decrease

Equivalent wave height capability:

Wave Direction	Maximum Wave Height	Condition
Head-on or beam (aligned with platform axis)	6-7 m (20-23 ft)	Synchronized float motion
Diagonal (45° to platform)	4-5 m (13-16 ft)	Maximum differential loading
Confused seas (multiple directions)	4 m (13 ft) significant	Random phase relationships

Design Capability Summary:

Normal Caribbean (non-hurricane): Fully capable with margin
Tropical storm approach: Capable with monitoring
Category 1 hurricane: Marginal - evacuation recommended
Category 2+ hurricane: Not designed for survival

6.2 Sea Anchor Benefits

Orientation to Waves - Significant Improvement

If a sea anchor keeps the seastead oriented into the dominant wave direction:

Eliminates diagonal wave attack (worst case)
All floats experience synchronized vertical motion
Cable load variation reduced by 40-50%
Effective wave capacity increases from 4-5 m diagonal to 6-7 m head-on

Recommendation: Deploy sea anchor or drogue when waves exceed 2 m to maintain heading into waves.

Sea Anchor Considerations:

Size: Parachute-style, 12-15 ft diameter for your displacement
Rode length: 300-500 ft of nylon line
Attachment: Bridle to forward floats (not living platform)
Swivel: Heavy-duty to prevent rode twist
Trip line: For retrieval

7. Cable Tension Adjustment

7.1 Why Adjustment is Needed

Initial stretch: Wire rope has constructional stretch (0.5-0.75%) during first loading cycles
Load changes: Adding/removing supplies, water, equipment changes buoyancy balance
Seasonal effects: Water temperature affects buoyancy slightly
Spring settling: New springs may settle slightly in first weeks
Cable wear: Minor elongation as wire rope beds in

7.2 Adjustment Mechanism Design

Recommended System: Turnbuckle with Lock

Location: Between spring and platform attachment point

Specifications:

Type: Jaw & jaw or jaw & eye turnbuckle
Material: 316 stainless steel or duplex
Working load limit: 12,000 lbs minimum
Thread size: 1" - 6 UNC
Take-up length: 12" (±6" adjustment)
Locking: Lock nuts on both ends + cotter pins

Adjustment Procedure:

Read spring extension (current tension)
Calculate turns needed (thread pitch × desired change)
Remove lock nuts/cotter pins
Apply penetrating oil if needed
Turn body with spanner wrench (both ends move equally)
Verify new spring extension
Replace lock nuts and cotter pins
Log adjustment in maintenance record

7.3 Adjustment Schedule

Period	Action
First week after installation	Check daily, adjust as needed for constructional stretch
First month	Check every 3 days
Months 2-6	Weekly inspection
After 6 months	Monthly inspection
After any storm (>2 m waves)	Immediate inspection
After load change (>1,000 lbs)	Check within 24 hours

8. Fatigue, Inspection, Cleaning, and Replacement

8.1 Fatigue Analysis

Loading Cycles Estimate:
Wave period: ~7 seconds average
Cycles per day: 86,400 / 7 = 12,343 cycles
Cycles per year: 4.5 million cycles
Design life: 10 years = 45 million cycles

Stress Range:
With spring compensators, cable load varies ±1,500 lbs typically
Stress range: ±4,500 psi (in 5/8" cable)
Mean stress: ~18,000 psi

Fatigue Assessment:
For duplex stainless wire rope, endurance limit ≈ 40,000 psi alternating
Stress range of 9,000 psi peak-to-peak is well below endurance limit
Expected fatigue life: >50 million cycles (ACCEPTABLE)

Spring Compensator Benefit:
Without springs, cable stress range would be 3-4× higher, potentially causing fatigue failure in 3-5 years. The spring compensators extend cable fatigue life to 15-20+ years.

8.2 Inspection Schedule and Procedures

Component	Frequency	Method	Criteria
Spring extension	Continuous (sensor) or Daily (visual)	Position measurement	Within 3"-7" range
Cable visible section	Weekly	Visual for broken wires, corrosion	No broken wires visible
End fittings	Monthly	Visual for cracks, corrosion, movement	No visible defects
Shackles and pins	Monthly	Check pin security, wear marks	Pins secure, <10% wear
Turnbuckles	Monthly	Check lock nuts, cotter pins, thread engagement	Minimum 6 threads engaged
Springs	Quarterly	Visual for cracks, corrosion, set	No visible damage, free length unchanged
Full cable length	Annually	Dive inspection or camera	Per API RP 2SM criteria
Cable diameter	Annually	Caliper measurement at 3 locations	<5% reduction from nominal

8.3 Cleaning Procedures

Above-Water Components (Springs, Turnbuckles, Upper Cable):

Frequency: Monthly or after salt spray exposure
Method: Fresh water rinse, soft brush for deposits
Avoid: Harsh chemicals, wire brushes on springs
After cleaning: Light spray of corrosion inhibitor (Boeshield T-9 or similar)

Underwater Cable Sections:

Frequency: Annually during dive inspection
Method: Soft brush to remove marine growth
Focus areas: Near end fittings where growth restricts inspection
Note: Some marine growth is acceptable and may provide cathodic protection

8.4 Replacement Criteria

IMMEDIATE REPLACEMENT Required If:

Any visible broken wires in cable
Cable diameter reduction >10%
Visible corrosion pitting >1mm deep
End fitting cracks or deformation
Spring crack or permanent set >5%
Shackle wear >15% of pin diameter

PLANNED REPLACEMENT (Schedule in next maintenance window):

Cable diameter reduction 5-10%
Surface corrosion >25% of visible area
Turnbuckle thread wear visible
Spring permanent set 2-5%
10 years service regardless of condition

8.5 Service Life Expectations

Component	Expected Life	Replacement Cost (Est.)
Duplex SS cable	15-20 years	$50-80/ft × ~400 ft total = $20,000-32,000
Swaged end fittings	Life of cable (replace together)	Included with cable
Metal springs	15-25 years	$3,000-4,000 each × 8 = $24,000-32,000
Turnbuckles	10-15 years	$300-500 each × 8 = $2,400-4,000
Shackles	10-15 years	$100-200 each × 24 = $2,400-4,800
Position sensors	5-10 years	$200-400 each × 8 = $1,600-3,200

9. Cable Replacement Procedure - Dual Attachment Points

9.1 Attachment Point Design

DUAL ATTACHMENT POINT DETAIL (Platform End) ┌─────────────────────────────────┐ │ Platform Structure │ │ │ │ ◎ Pad Eye A ◎ Pad Eye B │ │ │ │ │ └──────│──────────────│───────────┘ │ │ Turnbuckle A Turnbuckle B │ (spare/new) │ Spring A Spring B (spare) │ Shackle A Shackle B (for new cable) │ ═══════════════════════════════════ Active Cable New Cable (alongside)

Dual Pad Eye Specifications:

Spacing: 6-8 inches between pad eyes
Each pad eye rated for full cable load (12,000 lbs WLL)
Material: Duplex stainless steel, welded to structure
Hole diameter: 1-1/4" for 1" shackles
Backup plate on opposite side of structure

9.2 Load Transfer Procedure

Step-by-Step Cable Replacement:

Phase 1: Preparation (Calm conditions required, <1m waves)

Verify spare attachment point (Pad Eye B) is clear and undamaged
Install new spring assembly on Pad Eye B (unloaded)
Install new turnbuckle, fully extended (minimum take-up)
Rig new cable alongside old cable (may require diver for lower end)
Connect new cable to new spring assembly via shackle
Connect lower end of new cable to spare pad eye on float

Phase 2: Initial Tensioning

Use turnbuckle on new cable to take up slack
Monitor new spring extension - stop when spring begins to extend
Current state: Both cables sharing load (old cable ~80-90%, new cable ~10-20%)

Phase 3: Load Transfer

Gradually take up on new cable turnbuckle (1/4 turn at a time)
Simultaneously ease off old cable turnbuckle (same rate)
Monitor BOTH spring extensions continuously
Target: Equal extension on both springs (50/50 load sharing)
Continue transfer until new cable has ~90% load, old cable ~10%
Wait 15 minutes, verify stability

Phase 4: Old Cable Removal

Fully release old cable turnbuckle until old spring returns to free length
Verify new cable is carrying full load (spring at design extension)
Disconnect old cable lower shackle (may require diver)
Remove old cable, spring, turnbuckle assembly
Inspect old cable and components for failure analysis
Secure spare attachment point with dummy shackle/cover

Phase 5: Final Adjustment

Fine-tune new cable tension to design value (spring at 5" extension)
Install all lock nuts and cotter pins
Photograph new installation
Update maintenance log with new cable details
Plan to recheck tension after 24 hours, 1 week, 1 month

9.3 Critical Safety Points

SAFETY WARNINGS During Cable Replacement:

NEVER fully remove old cable before new cable is verified under tension
NEVER stand in line with cable under tension (snap-back zone)
ALWAYS have at least 2 persons for cable work
ABORT procedure if waves increase above 1.5m
Keep hands clear of turnbuckle and shackles when under load
Use proper rigging tools, not adjustable wrenches
Diver operations require surface support and communication

9.4 Tools Required for Cable Replacement

Turnbuckle wrenches (matched to turnbuckle size)
Shackle key or pin wrench
Torque wrench for lock nuts
Wire cutters (for safety wire/cotter pins)
Cotter pins and safety wire (replacement)
Penetrating lubricant
Corrosion inhibitor spray
Spring extension measuring tool or tape
Load cell (optional, for verification)
Camera for documentation
Dive equipment (if replacing underwater sections)

10. Complete System Summary

Final Design Specifications

Cables (8 required: 4 perimeter + 4 diagonal to platform)

Type	Duplex 2205 stainless steel wire rope
Construction	6×36 Warrington Seale, IWRC
Diameter	5/8" (16mm)
Breaking Strength	55,000 lbs minimum
Working Load	11,000 lbs (5:1 safety factor)
End Fittings	Swaged eye terminals, duplex SS

Spring Compensators (8 required)

Type	Helical tension spring
Material	17-7 PH stainless steel
Wire Diameter	0.625"
Outer Diameter	4.5"
Free Length	18"
Spring Rate	1,200 lbs/inch
Working Range	5" extension (6,000 lbs) ±3"
Maximum Load	12,000 lbs at 10" extension

Maximum Wave Capability

Head-on seas	6-7 m (20-23 ft)
Diagonal seas	4-5 m (13-16 ft)
Normal Caribbean	Full capability with large margin

Estimated System Cost

Cables (8 × ~50 ft avg)	$20,000 - 30,000
Springs (8 custom)	$24,000 - 32,000
Turnbuckles (8)	$2,500 - 4,000
Shackles (24)	$2,400 - 4,800
Position sensors (8)	$1,600 - 3,200
Pad eyes and hardware	$3,000 - 5,000
TOTAL	$53,500 - 79,000

11. Conclusions and Recommendations

Key Findings:

Slack cable risk is LOW for normal Caribbean conditions. Your design has sufficient static pretension that waves under 4m will not cause cable slack.
Spring compensators are highly recommended despite low slack risk, because they:
- Extend cable fatigue life by 3-5×
- Enable load monitoring
- Provide margin for unexpected events
- Allow easier tension adjustment
Metal springs are preferred over elastomeric or nylon for your above-water, monitored installation due to longevity and consistent properties.
5/8" duplex stainless cable provides adequate strength with appropriate safety factors.
Sea anchor deployment in waves >2m significantly increases safety margin by eliminating diagonal wave attack.
Dual attachment points enable safe cable replacement without removing the structure from service.

Important Limitations:

This analysis is preliminary and should be verified by a licensed marine structural engineer
Actual cable and spring specifications should be confirmed with manufacturers
Wave load estimates are approximate; site-specific wave data should be obtained
Hurricane evacuation is recommended for Category 1 or higher storms
Regular inspection and maintenance is critical for long-term reliability

Appendix: Supplier Resources

Duplex Stainless Wire Rope:

Bridon-Bekaert (bridon-bekaert.com)
WireCo WorldGroup (wirecoworldgroup.com)
Lankhorst Ropes (lankhorstropes.com)

Custom Springs:

Lee Spring (leespring.com)
Century Spring (centuryspring.com)
Diamond Wire Spring (diamondwire.com)

Marine Hardware (Turnbuckles, Shackles):

Suncor Stainless (suncorstainless.com)
Wichard (wichard.com)
Hayn Marine (haynmarine.com)

Position Sensors:

Celesco (celesco.com) - Draw wire sensors
Micro-Epsilon (micro-epsilon.com)