Boat Mechanics
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Boat Propellers - All you ever wanted to know

4 Lessons Intermediate

About this course

Propellers are the link between engine and water. Their job is to use the power generated by the engine to move water, causing a yacht that floats in that water and that is attached to the propeller to be pushed in the opposite direction.

This principle is quite clear and easy to understand. Only the implementation does not seem quite so simple: a clear indication that the propeller was patented in its present form for the first time 189 years ago and then remained virtually unchanged for 150 years; at that time, the design was largely based on empirical considerations in commercial shipping.

This situation did not change until the emergence of powerful computers capable of handling equations of computational fluid dynamics (CFD) emerging in the 1970's.

The recreational shipping is largely spared by this development until today. For about eighty years, the so-called Wageninger propellers have been used, which were empirically developed in tank tests at the Maritime Research Institute Netherlands (MARIN) in the tranquil town of Wageningen.

For the explanation of the operation of propellers, there are two views: The impulse observation, which explains how the acceleration of the water aft a thrust on the fuselage, and secondly the wing consideration, in which the propeller is considered as a wing, whose lift the thrust equivalent.

If one looks at the propeller geometry on the basis of these considerations, one can - fortunately without further mathematical justifications - gain fairly basic knowledge. Let's take a closer look at the impulse-changing wings!

The most important characteristics of a propeller are diameter, number of wings, area ratio and slope. With this information, it is already possible to estimate for which hull with which engine-gearbox combination this propeller could be used. In principle, one could at least approximately determine from the parameters of the propeller the yacht for which it is intended.

Propeller parts and designations

view from starbord side

view from stern

Course Structure

Planned for the Future

Introduction

Introduction to the history of propeller design and designations of the parts.

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Diameter

You will learn how the diameter of the propellor affects the performance and where the limitations are.

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Number of Wings

What is better: two or five wings? And why?

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Area Ratio

How is the area ratio defined and how can it be measured?

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