Verifying Tank Capacities: Water and Fuel Claims vs Reality
Updated: August 2026
Tank capacity is the most over-claimed figure in phinisi listings, because nobody checks it. Verify by three methods: read the general arrangement plan, sound the tanks physically, and run a metered fill. Fresh-water capacity governs how many days you can stay out; fuel capacity governs whether you reach Raja Ampat without a detour.
Why the number is routinely wrong
Capacity figures propagate. A yard quotes a design capacity, the first owner repeats it, a broker rounds it up, and eight years later the listing states a number that has never been measured against the tanks as built. Add the common practice of subdividing or partly decommissioning a tank during a refit, and the gap between the stated and the usable figure widens further.
There is also a definitional problem. Design capacity is the geometric volume of the tank. Usable capacity is what you can actually draw before the pickup starts sucking air, which on a poorly positioned pickup can be ten to fifteen per cent less. A listing quoting design capacity is not lying, but it is describing a number you cannot use.
Method one: the drawing
Start with the general arrangement plan, which shows tank positions and usually their individual capacities. Add them up. If the total disagrees with the listing, you have your first question. If the drawing shows four tanks and the engine room has three, the vessel has been modified. See reading a GA plan for the wider method.
Method two: sounding
Sounding means physically measuring the depth of liquid in each tank through a sounding tube, using a weighted tape, and converting depth to volume with the tank’s calibration table. Two things to insist on. First, that a calibration table exists at all — many phinisi have none, which means the gauge on the panel is an approximation someone estimated. Second, that the surveyor sounds every tank rather than sampling one.
Panel gauges on wooden vessels in the tropics are notoriously unreliable. Float senders corrode, and crews learn to read them as rough indicators. Treat a gauge reading as a suggestion and the sounding as the fact.
Method three: the metered fill
The definitive test, and the one that ends arguments. Draw the tank down, then fill through a metered pump and record the delivered volume. This is more practical for fresh water than for fuel, and it is worth doing on at least the primary water tank because water capacity determines cruising autonomy more directly than anything else on a liveaboard.
What the numbers mean operationally
| Figure | What it governs | Common failure |
|---|---|---|
| Fuel capacity | Passage range; whether long transits need a bunkering stop | Design volume quoted; usable volume 10–15% lower |
| Fresh water capacity | Days at anchor with a full guest complement | Assumes a working watermaker that is out of service |
| Watermaker output | Whether tank size is a constraint at all | Rated output quoted; membranes long past replacement |
| Black and grey water | Compliance in protected marine areas | Holding tanks absent or bypassed entirely |
That last row deserves emphasis. Cruising grounds within Komodo National Park and Raja Ampat are protected areas, and holding-tank capacity is an operational and reputational matter as well as a regulatory one. Check that holding tanks exist, are plumbed, and are not bypassed.
Turning the finding into a price position
If verified capacity comes in materially below the advertised figure, you have two options: adjust the offer by the cost of adding capacity, or accept the vessel as measured and plan itineraries around it. Either is reasonable. What is not reasonable is completing the purchase on the advertised number and discovering the truth on your first seven-day charter, with guests aboard and a water shortage on day five. The same discipline applies across the whole file — see listing red flags.
Request the vessel dossier
Ask whether tanks were sounded, and on what date, before accepting any capacity figure. WhatsApp +62 811-3941-4563 or write to [email protected]. All figures on this site are quoted in USD.
Frequently asked questions
How much fresh water does a phinisi need per guest per day?
Plan on a generous allowance once showers, galley and laundry are included; liveaboard operations commonly work to well over a hundred litres per person per day in practice. Tank capacity divided by that figure gives your true autonomy without a watermaker.
What is tank sounding?
Measuring the depth of liquid in a tank through a sounding tube with a weighted tape, then converting depth to volume using the tank’s calibration table. It is the standard verification method because panel gauges on older vessels drift badly.
Does a watermaker make tank capacity irrelevant?
No. A watermaker reduces dependence on tank size but introduces its own failure mode, and membranes degrade. Size the vessel’s autonomy on tank capacity alone, then treat watermaker output as margin rather than as the plan.
Are holding tanks required in Komodo National Park?
Protected marine areas impose discharge restrictions and expectations, and responsible operators maintain functional holding tanks regardless. Verify at survey that holding tanks are fitted, plumbed and not bypassed, because retro-fitting them is disruptive.
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.
