Strait of Hormuz Guidance: What Survey Managers Need to Know Now

What the Guidance Actually Says

On 20 May 2026 six industry bodies – the International Chamber of Shipping (ICS), BIMCO, INTERCARGO, INTERTANKO, IMCA and OCIMF – jointly issued “Guidance for Vessel Transit through the Strait of Hormuz.” It is industry guidance, not an IMO instrument, and it is written to support voyage-specific threat and risk assessment rather than to prescribe a fixed procedure. It complements the existing Best Management Practices for maritime security and keeps safety of life, safe navigation and protection of the environment as the primary considerations.

The headline navigational concern in the current environment is not congestion. It is electronic interference. GNSS jamming and spoofing across the Gulf and the approaches to the strait have become persistent, with independent monitoring recording large numbers of interference events in the area through early 2026. Vessels have reported satellite positions jumping ashore, freezing, or placing the ship inside another jurisdiction entirely, with associated AIS manipulation. The practical advice that follows from that is consistent across the guidance and supporting advisories: treat satellite positioning as advisory rather than authoritative inside the affected zone, cross-check continuously against radar, visual fixes and dead reckoning, and prepare the bridge to operate without a trustworthy GNSS fix.

For merchant shipping that is a watchkeeping discipline. For survey vessels carrying high-value positioning payloads and working to tight horizontal-uncertainty tolerances, the same interference touches the core of the survey itself.

Why This Matters for Survey Positioning

A survey positioning chain is built for the open sea. The primary GNSS feeds the survey solution, a backup receiver typically feeds navigation and AIS, and antennas are sited high and clear to suppress multipath. None of that is designed for a contested-RF corridor where the satellite signal may be denied or deliberately falsified.

Three positioning questions follow directly from the guidance.

First, AIS integrity. AIS must transmit continuously during transit; it cannot be silenced under way. The risk in the strait is not that AIS is off – it is that AIS is wrong. If the receiver feeding AIS is spoofed, the vessel broadcasts a confident but false position, and that error propagates into the traffic picture and into any logging that ties survey data to AIS time and position. Treat the AIS position as a sensor that can be compromised, not as ground truth.

Second, antenna exposure. The standard survey arrangement – antennas high and aft for a clear sky view – is also the most exposed to a jammer or spoofer. There is no antenna placement that defeats a strong local interference source, but resilient geometry, antenna isolation between primary and backup, and, where available, controlled reception pattern antennas (CRPA) materially improve resistance to jamming and spoofing. CRPA is a recognised anti-jam and anti-spoof measure recommended in industry guidance and supporting advisories for that reason.

Third, the fallback chain gets a real test. If the primary precise solution is lost or rejected as untrustworthy, the question is what the vessel falls back to and how good it is. A standalone GNSS fix is itself suspect in a spoofing environment, so the genuine fallback is non-satellite: inertial dead reckoning, radar ranging and visual fixes. For keeping the vessel in a traffic separation scheme whose lanes are roughly two miles wide, that fallback is adequate. For the survey solution it is a different order of problem: a creeping inertial drift or a spoofed jump of several metres is well inside the lane but far outside the horizontal-uncertainty budget the survey works to. Know how fast your inertial solution drifts without GNSS aiding, and know how you will detect that the satellite fix has gone bad in the first place.

The Reality on Deck

Most survey companies treat a strait passage as the master’s problem – something handled on the bridge while the survey team prepares equipment. In a jamming and spoofing environment that division does not hold. The interference that scrambles the bridge picture is the same interference that will corrupt the survey solution the moment work begins on the far side.

Spoofing is harder to manage than simple jamming because it is plausible. A jammer removes the fix; an alarm fires; the crew reverts to other methods. A spoofer leaves a clean-looking position that is wrong. The detection signs are indirect: the radar overlay drifts off the coastline, satellite counts move oddly, the electronic picture disagrees with what the watch can see. The discipline the guidance points to is continuous cross-checking – radar, visual and inertial held against the satellite fix at all times – so that a divergence is caught rather than trusted.

There is also a coordinate-frame trap that is easy to hit under VHF pressure. If the survey instrument and the AIS or ECDIS solution sit on different datums, realisations of WGS84, or antenna reference points, the two positions can differ by several metres even with no interference at all. That offset is immaterial to staying in a two-mile lane but corrupts the survey solution outright, and it muddies any reconciliation of the survey track against the reported AIS or ECDIS position. Resolve datum and antenna-offset consistency before entering the strait, not while explaining a coordinate shift over the radio.

Where Project Plans Fall Short

Reviewing transit plans for work in and beyond the Gulf, four gaps recur.

1. Treating Transit Time as Positioning-Neutral

A 12-to-24-hour transit is not idle time for the positioning chain. Receivers run throughout, and any configuration change forced by the passage – switching reference services, restarting equipment, changing antenna routing – can invalidate the baseline the survey assumed. Begin survey work without re-verifying after transit and you may start on a distorted baseline that only shows up against earlier campaign data.

2. Treating AIS as Navigation-Only

AIS is a position broadcast, and in a spoofing environment it is a position broadcast that can be falsified. If AIS and the survey solution are driven by different receivers, they can diverge – and under interference one of them may be actively wrong. Confirm which receiver feeds AIS and how a corrupted AIS position would be detected.

3. Under-Verifying the Fallback

Backup positioning is often assumed to be proven simply because it exists. The strait demands more: a fallback that holds up when the primary is denied or spoofed. That means a non-satellite layer – inertial, radar, visual – exercised in advance, with a known drift rate and a known detection method, not a standalone GNSS receiver that shares the primary’s vulnerability.

4. Ignoring Antenna and Interference Geometry

The ideal survey antenna position is the most exposed to interference. Course constraints in the traffic separation scheme can further limit satellite geometry and add radar multipath. None of this is fatal, but it has to be planned for – including the option of CRPA where the platform supports it – rather than discovered on entry.

Standards and Compliance Context

The guidance sits alongside the survey standards that govern accuracy. IHO S-44 defines hydrographic positioning accuracy by survey order: Order 1a, for example, sets a total horizontal uncertainty of 5 m plus 5 percent of depth at the 95 percent confidence level. A degraded or spoofed solution during transit does not affect the survey product as long as it is not used for the survey – but it makes a post-transit position check on a known control point mandatory before work resumes.

Inertial navigation is directly relevant here: IMCA’s guidance on inertial navigation systems (IMCA S 022) describes INS as a practical aiding and bridging solution for offshore survey, which is exactly the role it plays when GNSS is denied. Finally, ISPS security measures can restrict crew access to deck antenna positions during a transit, so any troubleshooting plan that assumes engineers can reach the antennas under way needs reviewing against the security regime in force.

What to Verify Before Mobilisation

The guidance does not change GNSS physics; it changes the operating environment the positioning chain has to survive. Before sailing into the affected zone:

Separate the primary and backup positioning chains so a single antenna or single point of failure cannot take down the survey solution and AIS together.

Confirm datum and antenna-reference consistency between the survey solution, ECDIS and AIS. A several-metre offset that is invisible against a two-mile lane still breaks a survey solution working to metre-to-decimetre tolerances.

Exercise the genuine fallback – inertial plus radar and visual – and record how quickly the inertial solution drifts without GNSS aiding, so the bridge knows how long it can hold position when the satellite fix is denied.

Establish how spoofing will be detected: continuous cross-checks of radar overlay, satellite count and visual fixes against the GNSS position, with a clear threshold for declaring the fix untrustworthy.

Where the platform supports it, assess CRPA or other anti-jam/anti-spoof antenna options, as recommended in industry guidance and supporting advisories.

Plan a post-transit verification on a known checkpoint before commencing survey work, and budget the time for it. Starting an acquisition campaign on an unverified baseline after a contested passage is the more expensive risk.

The guidance reflects that the Strait of Hormuz is now a contested electromagnetic environment in which satellite positioning cannot be trusted at face value. Survey vessels carry the consequences twice over: the same interference that degrades the bridge picture is a direct threat to positioning integrity. Resolve datum consistency, antenna geometry, fallback behaviour and spoofing detection in advance – not when the traffic picture and the survey solution have already started to disagree.

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Based on: Shipping industry provides guidance on traveling through Strait of Hormuz