1. Overview
The TheCharterBox Cargo Intake Calculator works out the maximum cargo a vessel can lift on a voyage. It evaluates the three limits that govern every dry cargo stem — deadweight, draft restrictions at each port, and cubic capacity — and tells you which one governs and by how much. Designed for charterers, operators, and brokers quoting intake before fixing.
The calculator runs entirely in your browser — results update instantly as you type. No software installation required.
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Three Constraints
Deadweight, per-port draft, and cubic capacity evaluated together — the governing limit is highlighted automatically.
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Draft & Density
Fresh Water Allowance and Dock Water Allowance computed per port from water density, with density-corrected TPC.
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Load Line Zones
Summer, Winter, and Tropical zones per port using the standard 1/48 rule.
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Bunker Burn-Off
Consumption between ports is deducted, so a draft limit at the discharge port is checked against the arrival condition.
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Stowage Factor & Units
Grain or bale capacity in m³ or ft³, stowage factor in m³/MT or ft³/LT, with broken stowage.
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Save, Share & PDF
Save calculations to your account, share a link that carries the full calculation, export a branded PDF.
2. Getting Started
Access the Calculator
Visit www.thecharterbox.com/cargo-intake-calculator/. No login required to use the calculator and see results.
Account Benefits
| Feature | Without Account | With Free Account |
|---|
| Use calculator & see results | ✅ | ✅ |
| Share link | ✅ | ✅ |
| Print calculation | ✅ | ✅ |
| Save to account | — | ✅ |
| Export PDF | — | ✅ |
Register free at www.thecharterbox.com/register/
The Card Flow
Vessel ParticularsDeductiblesPort RotationCargo & CubicResults
Work top to bottom: enter the vessel, deduct what is on board, define the port rotation, optionally add cubic limits — the Results card updates live as you type.
3. Vessel Particulars
- Enter Summer DWT (MT), Summer Draft (m), and TPC (MT/cm) — the three required vessel figures, all from the vessel’s particulars or Q88.
- Enter Summer Displacement (MT) so the calculator can derive the Fresh Water Allowance.
- If you don’t know the displacement, click “Don’t know displacement?” to enter Lightship instead (displacement = DWT + lightship), or enter the FWA directly from the load line certificate.
NOTE: If no FWA basis is provided at all, the calculator treats the Fresh Water Allowance as zero. That is the conservative assumption — in brackish or fresh water your real intake will be slightly higher than shown.
4. Deductibles
Everything on board that is not cargo. These are deducted from deadweight to find what is left for cargo.
| Field | Description | Typical |
|---|
| Bunkers ROB on Sailing | Fuel oil plus diesel/gas oil remaining on board when sailing from the load port | Voyage dependent |
| Fresh Water | Domestic plus technical fresh water | 100–250 MT |
| Constants | Stores, spares, crew effects, lub oils | 200–400 MT |
| Unpumpable Ballast | Ballast water that cannot be pumped out | Usually 0 |
5. Port Rotation
Enter the ports in voyage order — load ports then discharge ports (up to 6). Click “+ Add Port” to add a row, the red × to remove one.
KEY CONCEPT: Every port is checked independently. The governing draft limit is whichever port allows the least cargo — and for ports after the first, bunkers and fresh water consumed on passage are credited back, so the vessel is checked in its arrival condition, not its sailing condition.
| Field | Description |
|---|
| Type | Load or Discharge |
| Permissible Draft | The berth/channel limit in metres, allowing for the under-keel clearance you require |
| Water Density | Salt 1.025 / Brackish 1.015 / Fresh 1.000, or Custom (e.g. 1.020 for a river port) |
| Load Line Zone | Summer, Winter (−1/48 of summer draft), or Tropical (+1/48) — the zone in force where the vessel loads to that draft |
| Bunkers / FW Consumed | MT consumed since the previous port (hidden on the first port) |
In water less dense than salt, the vessel may load beyond her summer marks by the Dock Water Allowance, because she rises to her marks on reaching the sea. The calculator handles this automatically from the density you enter.
IMPORTANT: The calculation assumes full cargo is on board at every port in the rotation — it answers “what can I load such that no port is breached”. Rotations where cargo reduces between discharge ports are not yet supported.
6. Cargo & Cubic (Optional)
Expand the Cargo & Cubic card for voluminous cargoes where space, not weight, may govern.
- Choose Grain (free-flowing bulk) or Bale (bagged, baled, or breakbulk) capacity and enter it in m³ or ft³.
- Enter the cargo’s Stowage Factor in m³/MT or ft³/LT — unit conversions are handled automatically.
- Add Broken Stowage % for space lost to packaging and gaps (bagged cargo 8–15%, steel products 10–25%).
NOTE: Leave capacity or stowage factor blank and the cubic constraint is simply excluded — normal for dense cargoes like ore where cubic never governs.
7. Results
The Results card shows the maximum intake in large figures with a badge naming the limiting factor, a table comparing every constraint, and a sensitivity line quantifying what would buy you more cargo.
EXAMPLE: Vessel 55,000 DWT, summer draft 12.50 m, TPC 55, displacement 68,000 MT. Bunkers 900, fresh water 150, constants 300. Loading Rotterdam (13.50 m, density 1.020) for Iskenderun (11.60 m, salt water), burning 320 MT bunkers and 40 MT fresh water on passage. Result: 49,060 MT, draft-limited at Iskenderun — deadweight would allow 53,650 and Rotterdam 53,988, but the arrival draft at Iskenderun governs. Each extra centimetre of permissible draft there is worth about 55 MT of cargo.
The assumptions footnote states the method: linear TPC near the summer draft, no trim or hydrostatic-table interpolation, full cargo at every rotation port, and which FWA basis was used.
TIP: The sensitivity line is the negotiation lever. If the result is draft-limited, it tells you exactly what a deeper berth or a tide is worth; if deadweight-limited, every tonne of bunkers saved is a tonne of cargo.
8. Save, Load & Share
Saving (Logged-In Only)
- Click “Save” — the title pre-fills from the vessel name.
- Click “Load” to list saved calculations; click one to fully restore every field, or the bin icon to delete it.
Share Link (Everyone)
Click “Share” to copy a link that carries the complete calculation inside the link itself. Anyone opening it sees your exact inputs and results — nothing is stored on the server, and the calculation is not visible to anyone you don’t send it to.
9. PDF & Print
NOTE: PDF export requires a free account. Print works for everyone.
PDF — a branded document with vessel particulars, deductibles, the port rotation, the full constraint comparison, the governing result and sensitivity, and the assumptions footnote. File: cargo-intake-[vessel]-[date].pdf
Print — click “Print” or Ctrl+P. Enable “Background graphics” for colours.
10. Glossary of Terms
Broken StowageCargo space lost to packaging, dunnage, and gaps — entered as a percentage of capacity.
ConstantsStores, spares, crew effects, and lub oils — weight carried that is neither cargo nor bunkers.
Deadweight (DWT)The total weight a vessel can carry at her summer marks — cargo plus bunkers, water, constants.
DisplacementThe total weight of the vessel and everything on board; lightship plus deadweight.
DWADock Water Allowance — how much deeper than her marks a vessel may load in water between fresh and salt, scaled from the FWA by density.
FWAFresh Water Allowance — the amount a vessel may submerge her summer mark in fresh water; displacement ÷ (4 × TPC), in millimetres.
Grain / Bale CapacityCargo space measured for free-flowing bulk (grain) or for packaged cargo (bale); bale is always the smaller figure.
LightshipThe weight of the empty vessel — hull, machinery, and equipment, without cargo, bunkers, or stores.
Load Line ZonesSeasonal zones (Summer, Winter, Tropical) that adjust the permitted draft by 1/48 of summer draft.
Permissible DraftThe maximum draft a port, berth, or channel allows, including any under-keel clearance requirement.
ROBRemaining On Board — bunkers or fresh water still on board at a given point in the voyage.
Stowage Factor (SF)The volume one tonne of a cargo occupies — m³/MT or ft³/LT. High SF means light, bulky cargo.
TPCTonnes Per Centimetre immersion — the weight needed to sink the vessel one centimetre, near her summer draft.
11. Frequently Asked Questions
Do I need an account to use the calculator?
No. Use the calculator, see results, share links, and print without logging in. To save calculations and export PDF — register for a free account.
My results disappeared when I clicked “+ Add Port”. Why?
Results are held back while any port row is incomplete. Fill in the new port’s permissible draft — or remove the row — and the results return instantly.
Which water density should I use?
Salt 1.025 for sea berths, Fresh 1.000 for river berths well upstream, Brackish 1.015 for estuaries — or Custom with the figure from the port agent or pilot. Density matters twice: it sets the Dock Water Allowance and corrects the TPC.
When do I select Winter or Tropical zone?
Select the zone in force at the position and date the vessel is loaded to that draft, per the load line zone chart. Winter reduces the permitted draft by 1/48 of summer draft; Tropical increases it by the same.
Why does it say FWA is treated as zero?
You haven’t given the calculator a basis to derive the Fresh Water Allowance. Enter displacement, or lightship, or the FWA itself from the load line certificate. With no basis, FWA is zero — conservative, never optimistic.
What do “Bunkers Consumed” on later ports do?
They credit back weight burned on passage, so the vessel is checked at each port in her arrival condition. A draft restriction at the discharge port is therefore less costly than the same restriction at the load port.
Does it account for trim, hog/sag, or hydrostatic tables?
No. It uses the standard chartering method — linear TPC near the summer draft — which is the accepted estimation approach. For loading computer accuracy, use the vessel’s stability software. The assumptions are stated under every result.
Can cargo reduce between discharge ports?
Not yet. The calculation assumes full cargo on board at every rotation port. Partial-discharge rotations are planned for a future version.
Are the results binding figures?
No — they are professional estimates for quoting and planning. Final intake is always subject to the master’s stability calculation and actual conditions.
Does it work on mobile?
Yes. Fully responsive for desktop, tablet, and mobile.
How do I report a bug?
Email
[email protected] with what you entered and what you expected.
