Tonnage Certificates Explained: The Numbers Behind a Listing
Updated: August 2026
The surat ukur is Indonesia’s tonnage certificate: the official measurement document stating a vessel’s registered length, breadth, depth and gross tonnage. Gross tonnage is a measure of enclosed volume, not weight. It drives crewing requirements, certification class and fees, which is why a listing that quotes an estimated GT rather than a certified one is quoting nothing.
Volume, not weight — and why the confusion is expensive
Gross tonnage sounds like a mass and is not. It is a dimensionless figure derived from the total enclosed volume of the vessel. A phinisi with a large enclosed sky lounge can carry a higher gross tonnage than a longer hull with open decks. This matters commercially because thresholds in Indonesian regulation are expressed in GT, not in metres. A vessel that crosses a GT threshold moves into a different crewing and certification regime, and the cost difference is permanent.
Buyers routinely assume that a shorter hull is automatically the lighter regulatory burden. It is not. Always ask for the GT figure before assuming anything about the operating cost profile.
What is actually printed on the certificate
- Vessel name and call sign — these must match the registry entry and the grosse akta exactly.
- Registered length, breadth and depth — measured to defined points, and usually shorter than the length overall quoted in marketing.
- Gross tonnage and net tonnage — net tonnage represents the earning volume and is used for certain port dues.
- Place and date of measurement — the date tells you whether the certificate predates any visible modification.
- Measuring authority — issued through the harbourmaster office under the Directorate General of Sea Transportation.
Why marketing length and registered length disagree
A listing that says “35 metres” and a certificate that says 28.4 metres are not necessarily in conflict. Marketing length is normally length overall, measured from the tip of the bowsprit to the aft-most point of the stern platform. Registered length is measured between defined points on the hull and excludes those extremities. On a phinisi, where the bowsprit alone can run four or five metres, the gap is routinely six to eight metres.
Neither figure is dishonest, but only one of them is legally operative. When you compare hulls across listings, compare registered length against registered length, or you will conclude that a smaller vessel is larger. The size-class guides for the 20-metre, 30-metre and 40-metre classes all use the same basis so the comparisons hold.
The certificate as a fraud check
Because the surat ukur ties a specific measured hull to a specific registered name, it is one of the strongest identity checks available. Three cross-references are worth making before you commit:
- Certificate name and call sign against the grosse akta ownership deed. Any mismatch stops the transaction until it is explained.
- Certificate dimensions against the general arrangement plan. See reading a GA plan.
- Measurement date against the refit history. A 2016 certificate on a hull that gained an enclosed deck in 2022 means re-measurement is outstanding.
What happens if re-measurement is outstanding
The vessel must be re-measured and a fresh certificate issued before the registry entry can be corrected, and in practice before a clean transfer can complete. This takes weeks rather than days, and it can change the GT figure, which in turn can change the crewing and certification regime the new owner inherits. Discover this before you sign, not during flag transfer, when it becomes your delay rather than the seller’s.
Practical sequence for a buyer
Request the certificate at first contact, alongside the GA plan. Read the four numbers. Compare them with the marketing copy and note every gap. Then ask the seller to explain each gap in writing. Sellers with organised vessels answer within a day; the rest reveal themselves. Only then is it worth commissioning a surveyor, which is the point at which real money starts to move — see choosing a surveyor.
Request the vessel dossier
We supply the surat ukur alongside every listing dossier so the numbers can be checked before travel. WhatsApp +62 811-3941-4563 or write to [email protected]. All figures on this site are quoted in USD.
Frequently asked questions
What is a surat ukur?
It is the Indonesian tonnage measurement certificate for a vessel, stating registered length, breadth, depth, gross tonnage and net tonnage, issued through the harbourmaster office under the Directorate General of Sea Transportation.
Is gross tonnage the weight of the boat?
No. Gross tonnage is a dimensionless figure derived from enclosed volume. A vessel with more enclosed superstructure can carry a higher gross tonnage than a longer vessel with open decks, despite weighing less.
Why does the listing say 35m when the certificate says 28m?
Marketing normally quotes length overall including bowsprit and stern platform, while the certificate states registered length measured between defined hull points. On a phinisi the bowsprit alone often accounts for four to five metres of the difference.
Does gross tonnage affect how many crew I need?
Yes. Indonesian crewing and certification requirements are tiered by gross tonnage, so a vessel that crosses a GT threshold carries a different minimum manning and certification obligation for as long as it stays in that band.
Phinisi Boat For Sale is a specialist maritime brand and digital platform under Juara Holding Group. Vessel-sale, construction, refit and repair contracts are issued by PT Komodo Galangan Nusantara. Brokerage, central agency and charter-marketing contracts are issued by PT Komodo Bahari Nusantara. Separate contracts, separate fees, separate ledgers.
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Written and checked by the desk. Figures are dated at the point of writing — our editorial standards explains how, and what happens when something here turns out to be wrong.
