This calculator uses the same formulas as the Heliciel propeller design software.

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Propeller pitch calculator

This free marine propeller calculator starts from your requirement — diameter, thrust, speed of advance — and names the Wageningen B-series propeller that meets it at the best efficiency, with its pitch and its shaft speed.

Which B-series propeller for your boat?

The calculator sweeps the whole B-series — 3 to 7 blades, 81 pitch ratios from 0.60 to 1.40 — checks the blade area needed to avoid cavitation (Keller approximation), and keeps the most efficient propeller among those that qualify.

Propeller diameter mm — the largest the hull allows Required thrust N Speed of advance m/s Fluid Density kg/m³ — editable Shaft immersion m below the surface — for the cavitation check Vapour pressure of the fluid Pa — editable Where does the propeller work?

Enter your requirement and press the button.

Open-water diagram of the selected propeller: K_T, 10 K_Q and efficiency against advance ratio J. The dot marks how it works on your duty.

Outside the range of the series this calculator refuses to answer and says why: a regression extrapolated beyond its tests would return a number, not a measurement. Efficiency is open-water, bare propeller, with no hull and no shafting.

B screw Series propeller models

Turn a model with the mouse, read its characteristics, download its STL file for 3D printing, CAD or a CFD mesh.

STL files are exported in metres: if your CAD software opens the propeller at one thousandth of its size, set the import unit to metres.

These models are examples. The complete series — every blade number, every blade area ratio, every pitch ratio, at your diameter — is built from the B screw Series tool of the Heliciel software, which generates the geometry and exports it. And above all, the same window then lets you optimise that propeller to measure for your duty, instead of settling for the nearest one. Here is how.

The B-screw series tool in Heliciel, step by step

Step 1 — the three numbers that define a B-series propeller

Heliciel B-screw series window: diameter, blade number and blade area ratio — The entries name the propeller: **B3_35_** is three blades and A_E/A₀ = 0.35.

Diameter, blade number from 3 to 7, then a blade area ratio taken from the list belonging to that blade number — these lists hold only the geometries actually built and towed. An area ratio typed freely would leave the tabulated series, and the measured figures with it.

Step 2 — read the operating point

Open-water diagram of the B3-35: thrust and torque coefficients and efficiency against advance ratio J — Open-water diagram of the B3-35 at P/D 1.00, and the figures of its efficiency peak.

The Series performance tab carries the third number, the pitch ratio P/D between 0.60 and 1.40, and draws what the towing tank measured for the series so defined: K_T, 10 K_Q and the open-water efficiency against the advance ratio J. The marker sits on the efficiency peak — 74.4 % at J = 0.882 for this one. Below the diagram, the same point in figures, the bollard-pull landmark K_T at J = 0, and the pitch in millimetres for the diameter you entered.

Step 3 — let the software find the propeller

Best propeller tab: the B-series propeller selected for 9000 N at 3 m/s on a 1140 mm diameter — 1140 mm, 9 000 N at 3 m/s in sea water: the series answers B3-35 at P/D 0.79, 336 rpm, 58.1 % open-water efficiency.

The Best propeller tab reverses the question: diameter, thrust, speed and the fluid of your project, and it returns the propeller of the series that delivers that thrust at the best efficiency, with the shaft speed it requires. It is the calculation of this page, run on your project's fluid. Underneath, Keller's criterion gives the smallest blade area ratio that keeps that thrust clear of cavitation, and says whether the one selected is enough.

Step 4 — turn the selection into a blade

The B3-35 B-series marine propeller in Heliciel's 3D prototype view — The B3-35 chosen at step 3, carried into the project: 1140 mm, 3 blades, P/D 0.79, ready for STL export.

Three buttons carry the result into the project: the chord distribution alone, chords and profiles, or the complete geometry with the pitch settings — reverse engineering. From there the propeller is an ordinary Heliciel project: profiles, twist and chords become editable again, and the blade element momentum calculation works on your fluid, your speed and your rpm.

A catalogue propeller, or one made for your job?

A series propeller carries one pitch law for the whole family. Yet a blade does not meet the same flow at every radius: a single law cannot put all its sections at their best angle of attack. Blade element momentum sets the twist of each element for your operating point, and lets you choose a profile per element.

What is fixed, and what you can still decide
	B-series model catalogue propeller	Heliciel design made to measure
Blade outline	fixed by the family	free, and optimizable
Blade sections	those of the series	chosen element by element, with their polars
Twist	the pitch law of the family	computed element by element for your operating point
Operating point	one advance ratio	your speed, rpm, fluid and immersion
Reynolds number	2×10⁶, the towing tank's	the one your propeller actually works at
Off-design behaviour	not described	performance maps over speed and rpm
Cavitation, structure	not covered	checked on your blade
Result	a geometry to copy	STL, IGES, STEP, OBJ — and CFD in the PRO version

Design your own propeller with Heliciel

The vocabulary, in brief

Pitch is the distance a propeller would advance in one turn in a solid nut. Divided by the diameter it gives the pitch ratio P/D, dimensionless, by which every series is catalogued. The pitch angle of a section at radius r satisfies tan φ = P / (2πr) — steep at the root, shallow at the tip. Water not being a nut, the propeller never advances by its full pitch: the shortfall is the slip, the sign that it is working. Its dimensionless form is the advance ratio J = V / (n D), the abscissa of every open-water diagram. The shaft speed comes out of the calculation without being supplied thanks to the load coefficient K_T / J² = T / (ρ V² D²), which does not contain it.

Further reading: geometric and effective pitch, the variable pitch propeller, apparent speed and angle.

Frequently asked questions

How do I calculate propeller pitch from rpm and speed?

Divide the engine speed by the gearbox ratio to get the propeller speed, then divide your speed of advance by that: the result is the distance travelled per revolution. Divide it by one minus the slip and you have the pitch.

What is a normal slip figure?

Between 10 and 20 % for a correctly propped motorboat, less on a fast, light hull, considerably more on a displacement hull or a heavily loaded working boat. These are rules of thumb, not measurements: slip changes with load, trim and rpm on the same boat.

Should I change diameter or pitch?

Diameter first: it has far more influence on thrust and efficiency than pitch, and it is usually limited by the tip clearance the hull allows. Once the diameter is fixed at the largest value that fits, pitch is what sets the rpm the engine will reach.

Is the Wageningen B-series suitable for my propeller?

It was developed for marine propellers of conventional shape, with segmental and aerofoil sections, operating without cavitation at a Reynolds number of 2×10⁶. It is an excellent starting point for a boat propeller and a poor one for an air propeller, a wind turbine or a ducted fan — those need blade element momentum calculation with aerofoil polars of their own, which is what the Heliciel software is for.

Does this calculator replace a design?

No. It gives you the pitch and the efficiency of a known family of propellers — a catalogue geometry, frozen in a towing tank decades ago. It does not choose the profile of your blade sections, it does not compute the twist that would put each of them at its best angle of attack on your duty, it does not check cavitation at your immersion depth, and it does not tell you what happens away from the best efficiency point. Those are design questions, and they are what the Heliciel software answers.