A number without a unit can make a vessel look bigger, stronger or cheaper than it really is. This guide explains which figures to ask the seller for, which to accept only with documents, and how to compare the prices of two vessels fairly.
I am Pooria Adli, and every day at Shipo Market I deal with vessel sale and purchase listings. The most common mistake buyers make is this: they put two listings side by side, see two numbers and decide which vessel is cheaper. But those two numbers often do not measure the same thing at all. Get this wrong at the start and the whole negotiation is built on a crooked foundation.
Each vessel is measured with its own yardstick
The first rule is simple. The capacity of each vessel is measured with the yardstick specific to its type. Barges and landing craft are described by DWT. Tugs by horsepower. Passenger and support vessels by length. Crane barges by lifting capacity in tonnes, floating docks by lifting capacity, and floating workshops by light displacement.
Now imagine a seller who talks about “tonnage” for a tug, or gives only the length for a crane barge. Stop right there and ask: “What is the main measure for this vessel, and what is its exact figure?” This question is not hostile to the seller. A serious seller will be glad to hear it, because it shows the other side knows the business.
The variety of listings on Shipo Market shows the same thing. Most of our sale listings are tugs (41 listings), then general cargo ships (25 listings) and then barges (21 listings). These are three types in high demand, with three different yardsticks. Compare their prices directly and you will learn nothing useful.
Tugs: horsepower is one thing, bollard pull is another
In a tug listing, the first thing that catches the eye is usually engine power. Horsepower (BHP) tells you the power of the engine, but a tug's job is to pull. Real pulling force is measured by bollard pull: the force a tug can exert on a line when stationary.
The gap between these two figures is filled by the propeller, the nozzle, the hull design and the actual condition of the machinery. For this reason, two tugs with the same horsepower may in practice have different pulling force. My advice is clear:
Ask the seller for the horsepower and check it against the engine specifications and documents. Ask for the bollard pull separately, and request a valid document or report for it. If this figure is given only verbally, treat it as a claim, not a technical specification. Whether you want a tug for harbour work, marine work or support duties, this is the figure that settles the question.
General cargo ships and barges: DWT, cargo capacity and deck
DWT is the total weight a vessel can carry: cargo, fuel, water, stores and crew. This differs from light displacement, which is the weight of the vessel itself. The classic error is to treat DWT as the same as net cargo capacity. If you plan to move cargo only, you need to know how much of that DWT is actually left for cargo.