Understanding Draft Survey in Shipping: An Easy-to-Follow Guide

Most people hear the phrase “draft survey” and immediately picture an old-school, overly technical process. In reality, a draft survey is just a careful way of figuring out how much cargo a ship has taken on or discharged.

Think of it as a weight check that uses the way the ship sits in the water to estimate the cargo weight.

If you are new to port logistics, you will interact with draft surveys more often than you think. You may not perform the measurements yourself, but the numbers show up in reports, settlements, and conversations with surveyors, terminals, and principals. Understanding the basics helps you talk confidently with everyone involved in the call.

This guide keeps things simple. We will walk through what a draft survey is, how draft survey calculations generally work, the typical steps surveyors follow, and how Base helps keep all the supporting documents and context organized.

What Is a Draft Survey in Shipping?

A draft survey is a method used to estimate cargo weight by reading the ship’s draft marks and comparing the vessel’s condition before and after operations. The draft marks show how deep the ship sits in the water at the bow, stern, and midship draft area. When the ship floats deeper, it means weight has increased. When it rises, weight has decreased.

But why take a draft survey at all?

Here is the easiest answer: It gives everyone involved a shared, physical measurement of cargo weight.

This matters because cargo declarations, tally counts, and documents like a Mate’s Receipt or the terminal’s figures can sometimes differ. The draft survey becomes an objective check that shows, based on how the ship floats, roughly how much cargo is on board.

Does a draft survey happen on every vessel?

Not always.

Draft surveys are most common on bulk carriers and breakbulk vessels, or anytime the cargo is measured by weight rather than container count or piece count. They are especially common when:

• Cargo is paid for by weight
• A buyer or seller requests a neutral measurement
• There are differences between tally sheets and declared cargo amounts
• A principal wants confirmation before signing off on final quantities

Container ships, tankers, and RoRos usually do not rely on draft surveys because they use other built-in systems to track onboard quantities.

What Is the Formula for a Draft Survey

Now that you know why draft surveys are taken, it helps to look at the basic formula behind them. Surveyors use a lot of supporting details to fine-tune the numbers, but the core idea is actually pretty straightforward.

A precise draft survey compares the ship’s weight before the cargo operation and after the cargo operation. The difference between those two weights gives the cargo weight.

In simple terms: Cargo Weight = Final Displacement − Initial Displacement

That is the heart of the calculation.

6 Steps in Completing Draft Surveys

Now that you have a feel for how the numbers work, let’s look at how a draft survey method plays out in real time. Below is a simple walkthrough of the steps and the parties involved.

1. Take Initial Readings: Surveyors read the draft marks at multiple points along the hull. Photos are often taken to create a clear record. Any visual conditions, such as uneven water surface movement, are noted.
2. Confirm Tanks and Consumables: The crew and surveyors review ballast tanks, ballast water levels, empty double bottom tanks, fuel oil quantities, and fresh water figures. These numbers affect the net displacement and help confirm the vessel’s weight before cargo operations begin.
3. Record Water Density: A hydrometer reading is taken to measure the dock water density. The average density may be used if multiple readings are taken across the berth.
4. Review the Hydrostatic Information: Hydrostatic tables and the ship’s hydrostatic data are used to identify the corresponding displacement at each draft level. These tables help apply trim correction, correct trim figures, and other draft corrections needed to produce accurate measurements.
5. Calculate the Net Displacement: Once all inputs are reviewed, surveyors determine the net displacement for both the initial and final draft survey. This helps accurately determine the cargo weight.
6. Finalize and Compare: The cargo quantity is calculated and compared to documents like a tally sheet or Mate’s Receipt. This also ties into related operational paperwork, including items such as a Bunker Delivery Note or the port’s handover package.

These steps look detailed on paper, but in practice the flow becomes familiar once you see a few surveys completed. The biggest challenge is keeping track of the surrounding documentation, which is where Base comes in.

How Base Helps with Draft Surveys

Draft surveys rely on solid organization. The readings and draft survey calculations may be handled by surveyors, but the background work falls on agents. You need photos of draft marks, hydrometer readings, consumable logs, port data, and all the supporting files stored somewhere reliable. This is where Base becomes a practical asset.

Base does not calculate cargo weight, but it keeps the draft survey process clear by storing everything tied to the port call in one place. Agents can attach draft readings, tank records, and port information directly to the job timeline. The platform becomes a clean record the moment someone needs to revisit a detail.

For example, if a principal asks for water density records or wants to compare the draft survey results with tally data, you can pull everything from a single job. If a port provides updated port data or draft restrictions, it appears alongside all other call-related documents. This also includes tracking files that naturally sit beside surveys, such as the tally sheet documentation for cargo counts.

Base makes collaboration during the operation more straightforward. Teams can share readings, upload files, and stay aligned without scattering details across email chains. The system becomes a reliable memory that keeps the story of each call intact. It protects the context behind the numbers so you can answer questions confidently long after the vessel has sailed.

Conclusion: Draft Survey in Shipping

Draft surveys look technical from the outside, but once you understand the basics, the process becomes much clearer. You are simply comparing how the ship floats before and after cargo operations and using that information to estimate the cargo weight.

Surveyors handle the calculations, but agents support everything around them. That includes port data and all the day-to-day details that give the survey its context.

This is where the right system makes a difference. When every file, message, and record from the port call lives in one place, the draft survey becomes easier to follow and easier to explain to principals, surveyors, or terminals later.

Base helps with exactly that work. It keeps the full story of the call organized, so nothing gets lost in an inbox or buried in a shared drive.

If you have never used Base during a port call, trying it once with a draft survey in mind is a great way to see the value. You will notice how much simpler it feels to keep everything tied together. A cleaner job record makes it easier to support the survey, answer questions quickly, and move through settlement with more confidence.

Key Takeaways

• A draft survey compares how the ship floats before and after cargo operations to estimate cargo weight.
• Readings like draft marks, water density, and trim all contribute to getting a reliable number.
• Surveyors handle the calculations, but agents support the process by keeping documents, photos, and records organized.
• Draft survey results often tie back to other port call documents, such as tally sheets or Mate’s Receipts.
• Using Base during a port call makes it easier to keep everything in one place so you can answer follow-up questions quickly and confidently.

Frequently Asked Questions