It is the first question, and it is genuinely harder to answer than it should be: does my yacht actually need an Inventory of Hazardous Materials? The broad regulatory pages tend to answer for commercial ships and leave yacht owners to work out the rest. Here is the yacht-side version.

The headline thresholds

Two instruments set the scope, and they are scoped differently:

So the first filter is simple: 500 gross tonnage. Below it, neither regime brings the IHM obligation in the same way (though your flag State may have its own requirements — always worth checking).

Why gross tonnage is not length

Here is the trap. Gross tonnage is a measure of enclosed volume, not length, and the relationship between the two is not linear. A wide-beam, high-volume 44 m yacht can sit above 500 GT, while a sleek, low-volume 55 m yacht can sit below it. You cannot read your scope off the LOA on the brochure.

The number that matters is on your International Tonnage Certificate. If you are near the threshold, that certificate is the authority — not a rule of thumb about metres.

The EU port-call trigger

Even if your yacht is not EU-flagged, the EU SRR can still reach you. A non-EU-flagged yacht of 500 GT and above that calls at an EU port is expected to carry an Inventory of Hazardous Materials and a Statement of Compliance. For yachts that spend any part of the season in the western Mediterranean — Antibes, Palma, Genoa, Athens — this trigger is very easy to meet.

This is why a Cayman- or Marshall Islands-flagged yacht based in the Med is, in practice, usually planning for IHM regardless of the Convention: the EU port-call route already applied to it before the HKC arrived. (The two certificates relate to one shared inventory — we explain how in HKC ICIHM vs EU SRR Statement of Compliance.)

Private versus commercial

A common question: “We’re a private yacht — does this still apply?” The IHM obligation flows primarily from gross tonnage, flag, and where the vessel trades, rather than from private-versus-commercial status alone. But registration category can affect how the requirement is applied and which survey regime your flag administers. This is exactly the kind of detail to confirm with your flag State or class society rather than assume either way.

We deliberately do not give a blanket yes/no on private yachts here, because the honest answer is it depends on your specific registration — and getting that wrong in either direction is costly.

Build year does not get you out of it

One more myth worth killing: the Convention applies regardless of build year. An older yacht is not exempt because it predates the rules. What changes for older vessels is how the initial inventory is built when the original builder’s records are incomplete — through document review plus a visual and sampling check by a competent person. We cover that pathway in IHM on older superyachts.

A quick way to check

If you want a structured walk-through rather than a wall of conditions, our IHM applicability & deadline checker steps through flag, tonnage, build year, and EU port calls and tells you whether you are likely in scope and what the key date is. Treat it as a starting point — your flag State administration or class society confirms the exact obligation for your vessel.

And if the answer is “yes, in scope,” the next question is what an IHM actually involves day to day. That is what our complete guide to IHM for superyachts is for.

MANTIS is IHM compliance management software for superyachts. It manages Part I/II/III records, tracks certificate expiry and survey intervals, and generates survey-pack PDFs for class society review. Start free beta →