Underwater connectors and mating cables provide system flexibility, ease of service, and other advantages to undersea system designers and field engineers.

They also bring their own suite of added complications and problems.

There is a lot to consider. System designers need to be conscious of the connector they select. A criteria-of-selection provides a programmatic approach to narrowing down and choosing the right underwater connector. Sales reps can provide guidance, but it is ultimately the responsibility of the engineers to write the specifications.

I’ve always held that connectors are a mechanical problem first. If the seals don’t work, then what’s inside doesn’t matter anymore. Not that it wasn’t important to begin with. I also pressure test connectors to be sure there is no production flaw with any critical step. Best time to learn of a problem is onshore, weeks before deployment. Yes, it’s extra work. Your team is counting on you. Play like a champion.

What’s your application? Determining the need.

Underwater Connector Selection Criteria

1. Will the connector transfer power or signal?
2. What is the expected operating service depth and design safety factor?
3. What is the expected deployment duration or system service life?
4. What are the expected environmental conditions (cold, anaerobic, saline, etc.)?
5. Must the connector mate to an existing system?
6. Must the bulkhead connector retrofit to an existing hull penetration? Is a thread extender required for thick hulls? Are locking sleeves or retaining straps an option?
7. What is the available mounting space? Does it allow room for torque wrench installation?
8. Would a low-profile right-angle connector be appropriate? Can the contact orientation be rotated to an optimum position?
9. Must the connector have seal or contact redundancy?
10. What are the cost and delivery constraints?
11. Must the connector be underwater mateable? With power on?
12. Is the connector field serviceable? What level of technician skill is necessary?
13. Avoid dissimilar materials between the bulkhead connector and the housing that will lead to galvanic corrosion or cathodic delamination.
14. Are there any Mil Spec Requirements to be met?
15. Are there any other special requirements to be met (i.e., fiber optic, neutrally buoyant, Fluid filled/pressure balanced)?
16. What is the cable type to be wired and bonded to the connectors (i.e., twisted single pair, parallel bundle, coaxial, electromechanical)? What is the jacket material, construction, and fillers? Is it suitable for overmolding?
17. Is the instrument package designed to be handled in the field without danger to the connectors? To use handles, tagline rings, and cleats to prevent accidental damage to the connector? Is the connector protected from side impact? Can the cable be strain relieved?

Designers should consider the use of connectors of different pin counts or use of sockets rather than pins to differentiate connectors meant for different tasks. It ensures you’re plugging the right cable into the right port. The cost to order isn’t bad, but stocking spares is more of a challenge.
I pay attention to the manufacturer’s engagement sequence that makes certain the pins and sockets are aligned before plugging together, such as key/keyway or an alignment pin. Many rubber molded connectors use an asymmetric pin/socket pattern to confirm proper alignment.

• Interchangeability: Rubber molded connectors provide greater tolerance of mated parts, and even some room for center-to-center pin differences, giving the best chance for mixed manufacturers’ parts working together. Pin lengths and diameters may vary, though. Hard shell connectors are not as forgiving. As a rule, stick with the same manufacturer for mating connectors. No manufacturer can reasonably guarantee another manufacturer’s tooling and production quality—nor should they be expected to. If a mated pair doesn’t work, it’ll be the engineers who have to figure it out.
• Selecting a manufacturer: Ask if they sell in small volumes. Do they have a stocking distributor? What sort of inventory do they normally carry? Who else uses them? The industry has come a long way in the past 40 years, and many of the basic problems, such as o-ring seal design to Parker Spec, have been resolved.

A 20-inch Vitrovex hollow borosilicate glass sphere is fitted with feedthroughs, making it a self-buoyant instrument housing. Credit: Steffen Pausch, Nautilus Marine Service, Buxtehude, DE

Use of this checklist during the early design phase of a new underwater system will assist the designer or program manager avoid predictable problems with these fundamental underwater system components. Work with your intended supplier; they want you to be successful, too.

Follow-on: This story is about selecting the best connector for your application. There are many details following that: installation, greasing lightly, “burping” rubber molded connectors, cable splices, cable bend radii, cable strain reliefs, and other important matters. Ask lots of questions of others in the field, look at what choices other people have made, and start to build your own preferences based on experience. It’s an exciting and evolving industry, filled with good people.

Underwater Connector Companies to Consider

Acknowledgements

I learned a lot from Ray Hayworth, General Dynamics Electric Boat Division, who shared his experience broadly, spoke at MTS cable and connector conferences, and published design guidelines for use at Electric Boat. R. Frank Busby’s Manned Submersibles text is still a classic and available as a free download (https://archive.org/details/mannedsubmersibl00busb). Bob Wernli and Bob Christ’s “The ROV Manual: Second Edition,” has a lengthy chapter on cables and connectors. Thanks to Andy Gardener, Teledyne Impulse, who suggested revisiting this topic.
“Lander Lab” is a hands-on column of Ocean Lander technologies, an often-overlooked class of unmanned undersea vehicles. It is meant to serve the ocean lander community in the manner of Make Magazine and other DIY communities.

Comments on this article, or suggestions for stories of interest to other Landereans are welcome. MTR invites you write to Kevin Hardy <[email protected]>.