Position accuracy underpins almost everything else on a modern bridge — ECDIS, AIS, autopilot and voyage recording all draw from the same GPS feed. Standard GPS is good enough for most open-ocean navigation, but there are operations where a few metres of error simply isn't acceptable. That's where DGPS comes in, and knowing when you actually need it can save a fleet operator from overspending on precision that isn't required.
Standard GPS: Accuracy and Limitations
A standard marine GPS receiver typically holds accuracy within a few metres under normal conditions. For open-water passage-making, this is more than sufficient — the vessel's position on the chart is accurate enough for safe navigation without any additional correction. Signal quality can still degrade near tall port structures or in areas with heavy satellite signal interference, which is worth factoring in for vessels operating mostly in congested harbours.
What DGPS Adds
Differential GPS uses a network of fixed reference stations that broadcast correction signals, improving accuracy down to sub-metre levels in many cases. This level of precision matters most for:
- Offshore platforms and drillships conducting dynamic positioning operations
- Dredging and survey work requiring precise, repeatable positioning
- Vessels operating in narrow channels or congested port approaches
- Anchor handling and mooring operations near fixed infrastructure
For a general cargo vessel running standard open-ocean routes, this level of precision is rarely necessary — the added cost of a DGPS receiver and correction service subscription is better spent elsewhere.
Redundancy and Backup Positioning
Because so many bridge systems depend on a single position feed, most vessels carry a secondary GPS receiver as a backup — either a second standalone unit or a dual-antenna configuration. This isn't excessive caution; a single point of failure on positioning affects ECDIS, AIS and autopilot simultaneously, so the backup unit is worth budgeting for from the outset rather than added later.
Antenna Placement
GPS antenna position affects signal quality more than most crews expect. Placement with a clear, unobstructed view of the sky — away from funnels, masts and other tall structures that can block or reflect signals — makes a measurable difference to fix reliability, particularly in poor weather.
GPS & DGPS Brands & Model Numbers We Work With
Most vessels we support are already running one of a handful of established GPS/DGPS brands. Here's a quick reference on the model numbers you're likely to come across, and what each is generally used for. Nautical Marine Services supplies units across all of these brands on an order basis — see our full GPS & DGPS range.
Furuno GPS
| Model | Notes |
|---|---|
| Furuno GP-33 | Compact standalone GPS navigator for smaller vessels |
| Furuno GP-39 | Standard GPS navigator with colour display |
| Furuno GP-150 | High-end GPS navigator, larger vessel fit |
| Furuno GP-170 | High-end GPS navigator, larger vessel fit |
Furuno GP-33 & GP-39
Looking for the Furuno GP-33 specification? This is a compact standalone GPS navigator for smaller vessels. We can confirm current GP-39 price and colour display configuration on request.
Furuno GP-150 & GP-170
The Furuno GP-150 GPS navigator and GP-170 GPS are the high-end units for larger vessel fit. Contact us for current price and availability on either model.
Looking to buy or replace a Furuno GPS unit? Send us your model number — we confirm current specification, price and lead time before you order.
Furuno GPS Compass (Satellite Compass)
| Model | Notes |
|---|---|
| Furuno SC-30 / SC-33 | Compact satellite compass for small to medium vessels, GPS/GNSS heading output |
| Furuno SC-50 | Second-generation satellite compass using GPS Kinematic technology with a 3-axis rate sensor |
| Furuno SC-70 | Commercial-grade satellite compass, 0.4° heading accuracy, maintenance-free with no moving parts |
| Furuno SC-130 | Higher-capacity satellite compass built on the same platform as the SC-70 |
| Furuno SCX-20 / SCX-21 | Satellite compass using GNSS antennas rather than a spinning mass to derive heading, increasingly fitted on newer vessels |
Furuno SC-30, SC-33 & SC-50
Looking for the Furuno SC-30 specification? These are compact satellite compasses for small to medium vessels. We can confirm current SC-50 price and 3-axis rate sensor configuration on request.
Furuno SC-70 & SC-130
The Furuno SC-70 satellite compass delivers 0.4° heading accuracy with no moving parts. Ask us for current SC-130 price and availability for larger vessel fit.
Looking to buy or replace a Furuno GPS compass? Send us your model number — we confirm current specification, price and availability before you order.
JRC GPS Compass
| Model | Notes |
|---|---|
| JRC JLR-21 | GPS compass unit combining heading and position output |
| JRC JLR-31 | GPS compass unit combining heading and position output, larger vessel fit |
| JRC JLR-7600 / 7900 Series | Standard GPS receiver series |
| JRC JLR-7500 / 7800 Series | Standard GPS series with added DGPS correction capability |
JRC JLR-21 & JLR-31
Looking for the JRC JLR-21 specification? This GPS compass unit combines heading and position output. We can confirm current JLR-31 price for larger vessel fit on request.
JRC JLR-7600/7900 & JLR-7500/7800 Series
The JRC JLR-7600 series is a standard GPS receiver line, while the JLR-7500 series adds DGPS correction capability. Contact us to confirm which fits your vessel and current pricing.
Looking to buy or replace a JRC GPS compass unit? Send us your model number — we confirm current specification, price and availability before you order.
Hemisphere GNSS Compass
| Model | Notes |
|---|---|
| Hemisphere V123 / V133 | All-in-one smart antenna offering decimeter-level position with heading |
| Hemisphere VS330 | Dual-antenna setup for higher-accuracy heading and RTK positioning |
| Hemisphere V200 / V500 | Dual-antenna setup for higher-accuracy heading and RTK positioning |
Hemisphere V123, V133 & VS330
Looking for the Hemisphere V123 specification? This all-in-one smart antenna offers decimeter-level position with heading. We can confirm current VS330 price and RTK positioning configuration on request.
Looking to buy or replace a Hemisphere GNSS compass? Send us your model number — we confirm current specification, price and availability before you order.
SeaStar DGPS System (Fugro)
| Model | Notes |
|---|---|
| SeaStar 3510LR | Widely fitted on offshore and survey vessels |
| SeaStar 3610 | Widely fitted on offshore and survey vessels |
| SeaStar 9205-GNSS | Common on dynamic positioning platforms needing multi-constellation coverage (now succeeded by the 9410-AUT) |
| SeaStar 9410-AUT | Current-generation successor to the 9205-GNSS for dynamic positioning platforms |
SeaStar 3510LR & 3610
Looking for the SeaStar 3510LR specification? These are widely fitted DGPS units on offshore and survey vessels. We can confirm current SeaStar 3610 price and availability on request.
SeaStar 9410-AUT
The SeaStar 9410-AUT is the current-generation successor to the 9205-GNSS for dynamic positioning platforms needing multi-constellation coverage. Ask us for current price and lead time.
Looking to buy or replace a SeaStar DGPS system? Send us your model number — we confirm current specification, price and availability before you order.
Trimble GPS and DGPS
| Model | Notes |
|---|---|
| Trimble SPS351 | Modular DGPS/beacon receiver built for marine construction and survey work |
| Trimble SPS356 | Modular DGPS/beacon receiver built for marine construction and survey work |
| Trimble SPS361 | Adds dual-antenna heading output alongside position data |
| Trimble SPS461 | Adds dual-antenna heading output alongside position data |
Trimble SPS351 & SPS356
Looking for the Trimble SPS351 specification? These are modular DGPS/beacon receivers built for marine construction and survey work. We can confirm current SPS356 price and availability on request.
Trimble SPS361 & SPS461
The Trimble SPS361 and SPS461 add dual-antenna heading output alongside position data. Contact us to confirm which fits your vessel and current pricing.
Looking to buy or replace a Trimble GPS or DGPS unit? Send us your model number — we confirm current specification, price and availability before you order.
Frequently Asked Questions – GPS & DGPS Models
What is the Furuno GP-150 specification?
The GP-150 is Furuno's high-end standalone GPS navigator built for larger vessel fit. Contact us for the full specification sheet, current price and lead time.
Where can I buy a Furuno SC-70 satellite compass or spare parts?
We supply the SC-70 and its spare parts to order. Send us your vessel type to confirm current availability and price.
What is the difference between JRC JLR-7600 and JLR-7500 series?
The JLR-7600 series is a standard GPS receiver line, while the JLR-7500 series adds DGPS correction capability. We can confirm which fits your vessel's operating requirements.
Is the SeaStar 9205-GNSS still available as a replacement unit?
The 9205-GNSS has been succeeded by the 9410-AUT, but we can still source replacement units and spares for vessels running the earlier model — contact us to confirm current availability.
What is the current Trimble SPS361 price?
Pricing depends on configuration and antenna setup. Send us your vessel details for an accurate quote on the SPS361 or SPS461.
Does the Hemisphere V123 support RTK positioning?
The V123/V133 offers decimeter-level position with heading as an all-in-one smart antenna. For higher-accuracy RTK positioning, the dual-antenna VS330 or V200/V500 series is the better fit — we can confirm which suits your operations.
How do I identify which GPS or DGPS model my vessel is running?
A photo of the display unit and antenna nameplate is usually enough for us to confirm the exact model and current availability.
Quick Checklist Before You Order
- Confirm whether your operations actually require DGPS-level accuracy
- Check DGPS correction signal coverage for your operating region
- Plan for a backup receiver or dual-antenna setup
- Position antennas with a clear, unobstructed sky view
Once you've confirmed your specification, Nautical Marine Services can check availability from our GPS and DGPS range and arrange delivery to your vessel's next port of call.
Need a GPS or DGPS Receiver Fitted to Your Vessel?
Nautical Marine Services works on an order basis — share your vessel type and operating area, and we'll help you decide between standard GPS and DGPS from our GPS & DGPS range.
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