Marine and subsea slip rings
Moog Model 303 downhole marine and subsea slip ring
Oil-filled slip rings for high-temperature, high-pressure downhole tools, in miniature-bore, large-bore and 20-channel high-voltage versions.
Key specifications
| Circuits (max) | 20 |
|---|---|
| Current per circuit (max) | 10 A |
| Voltage (max) | 1,000 V |
| Speed (max) | 600 rpm |
| Bore | 9.525–88.9 mm |
| Temperature (max) | 230 °C |
Summarised in our own words from Moog Inc.'s published data; series maxima, individual models vary. Last checked 2026-10-29. Source 1 · Source 2
Notes on this data
Pressure 25 kpsi (1,700 bar). 200 °C standard, up to 230 °C. Type marine used as closest energy category.
Specify Motion is not affiliated with Moog Inc.. Moog and Model 303 downhole are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Typical applications
Alternatives that meet or exceed these figures
Engineers often come to us with a Moog part number and leave with an alternative that is easier to source, quicker to deliver or a better fit for the machine. These 3 series from our supply network are the closest match on published figures.
Sealed slip rings rated IP64 to IP68 for wet, washdown and marine settings such as ships and harbour equipment.
| Published maximum | Model 303 downhole | Waterproof Slip Ring |
|---|---|---|
| Circuits | 20 | 44 meets or exceeds |
| Current per circuit | 10 A | 85 A meets or exceeds |
| Speed | 600 rpm | 600 rpm meets or exceeds |
| Voltage | 1,000 V | 1,100 V meets or exceeds |
| Bore | 88.9 mm | 127 mm meets or exceeds |
Heavy-duty carbon-brush slip rings for very high current and voltage, with copper-graphite power rings and precious-metal signal rings. Large and heavy by design, but straightforward to maintain.
| Published maximum | Model 303 downhole | BHR Series Frameless Type (Carbon Brush) |
|---|---|---|
| Circuits | 20 | 76 meets or exceeds |
| Current per circuit | 10 A | 500 A meets or exceeds |
| Speed | 600 rpm | 10 rpm |
| Voltage | 1,000 V | 20,000 V meets or exceeds |
| Bore | 88.9 mm | — |
Large through-hole slip rings for heavy outdoor plant, with through holes quoted up to 1000 mm and long service life.
| Published maximum | Model 303 downhole | Large Size Slip Ring |
|---|---|---|
| Circuits | 20 | 35 meets or exceeds |
| Current per circuit | 10 A | 50 A meets or exceeds |
| Speed | 600 rpm | — |
| Voltage | 1,000 V | 500 V |
| Bore | 88.9 mm | 1,000 mm meets or exceeds |
Figures are the highest published for each series and are not always measured the same way. A higher figure is not automatically a better choice: mounting, duty cycle, feedback, connectors and approvals matter too. An engineer will check the fit against your application before recommending anything.
What a marine and subsea slip ring is
A marine slip ring is a rotary joint built to survive salt air, spray, condensation and, for subsea versions, immersion and external pressure. The electrical design is conventional, with power, signal and data rings, but the housing uses corrosion-resistant materials such as stainless steel or marine-grade aluminium, robust shaft seals and suitable connectors. Subsea units are commonly oil-filled and pressure-compensated so internal pressure matches the surrounding water, which keeps seals working at depth.
When engineers choose a marine and subsea slip ring
Choose a marine design for deck winches, cranes, mooring and cable reels on ships and offshore platforms, and for ROVs and other subsea vehicles. A standard industrial unit in an enclosure is sometimes adequate in sheltered locations, but salt and condensation shorten life quickly. The trade-offs are size, weight, cost and lead time. For subsea work, compensated designs add complexity but avoid relying on seals to hold back full pressure. Fibre and high-voltage channels are often needed alongside power.
How to specify the Moog Model 303 downhole
Send these with your enquiry and an engineer can confirm the right Model 303 downhole variant or an equivalent:
- Location: deck, splash zone or subsea, with depth rating (m)
- Ingress protection (IP code) and pressure compensation method
- Housing and shaft materials
- Power circuits, current and voltage (A, V)
- Data or fibre channels
- Speed (rpm) and duty
- Connectors, glands and cable types
Common mistakes to avoid
- Using an industrial slip ring in a box on deck, where condensation forms inside
- Mixing metals that corrode galvanically in seawater
- Overlooking high-voltage clearance on winch slip rings feeding subsea power
- Not specifying compensation fluid and service intervals for oil-filled designs
Moog Model 303 downhole: frequently asked questions
What is the Moog Model 303 downhole?
Oil-filled slip rings for high-temperature, high-pressure downhole tools, in miniature-bore, large-bore and 20-channel high-voltage versions. Published series figures include circuits 20, current per circuit 10 A, voltage 1,000 V, speed 600 rpm. It is made by Moog Inc.; Specify Motion can help source it or propose an equivalent.
Who makes the Moog Model 303 downhole?
The Moog Model 303 downhole is made by Moog (Moog Inc.) and is listed here for engineers comparing options. Specify Motion is not affiliated with Moog Inc.; brand names are used only to identify the product.
What is the circuits of the Moog Model 303 downhole?
The published series maximum circuits is 20. Individual models and sizes in the Model 303 downhole range vary, so check the exact variant against your duty cycle, mounting and environment, or ask our engineers to confirm the right size for you.
Is there an alternative to the Moog Model 303 downhole?
Yes. On published figures, Waterproof Slip Ring and BHR Series Frameless Type (Carbon Brush) are the closest match from our supply network. An engineer confirms the fit against your application before recommending anything.
What does pressure-compensated mean for a subsea slip ring?
A pressure-compensated slip ring is filled with an insulating oil and linked to a flexible bladder or piston that lets the surrounding water pressure act on the oil. Inside and outside pressures stay nearly equal, so seals only have to keep fluid in, not resist full depth pressure. This is common for ROV and deep-water equipment because it makes depth rating far less dependent on wall thickness.
Is IP68 enough for a marine slip ring?
IP68 means protected against continuous immersion under conditions agreed by the manufacturer, so the actual depth and duration must be stated alongside it. It does not cover corrosion, UV, salt fog or pressure cycling. For deck equipment, specify materials and sealing for salt spray and condensation. For subsea, give the rated depth and test pressure, not just an IP code.
Further reading: Waterproof and subsea slip rings · How to select a slip ring · Slip rings
Other marine and subsea slip rings series
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