A propeller is to a boat as a wheel is to car, and replacing the propeller is a challenging task, not so much in terms of actually fitting in the new piece but hunting for the proper type, specifically if you want to buy a used one.
In our previous article we learnt about various tips to buy a used marine diesel engine but an engine without propeller is as useless on a boat, as the engine in your car without wheels. So let us take a look at some of the tips to buy a propeller.
Like before let me remind you that buying a propeller (prop for short) is only a problem if you want to buy a used propeller because if you are interested in getting a new one, you can simply look up at the make or model number of the old prop and order the new one.
Here is some common terminology associated with props as you can correlate with image above
- Pitch – this refers to the distance moved by the boat corresponding to one full revolution of the prop
- Rake – this refers to the angle between the blade and the propeller hub
- Cupping – this refers to the curled edge of the blade which helps to improve grip of the propeller in water
It must be remembered that blade size is given as Diameter of the Blade * Pitch
Buying a used prop
Buying a used propeller is a challenging task because if you take a look at the websites which sell used props or go to a shop for this purpose, you will be simply overwhelmed with the choice available to you in terms of their makes, shapes, materials, size etc.
Since there is a high probability that you might end up buying a wrong prop at the first instance, the very first thing you should ask the seller is whether they offer a replacement assurance in case the prop doesn’t work with your engine.
When I say working with your engine, I do not only mean physical fitting. Any propeller with the right diameter compared to the shaft of the engine would fit in it, but that does not mean that it will perform its function in a proper manner.
Many props are made specifically for some specific boats and they only fit and perform in those vehicles. You might find a lot of useful information regarding what sorts of propellers might fit into your boat, otherwise you might want to experiment a bit by trying couple of changes.
The material of the prop is also important in deciding which one would be the best fit for your boat. Commonly used materials include aluminium, composite materials etc. another possibility is to use a prop which can blades that can be replaced individually instead of replacing the whole propeller, though you must realize that in such a case you would need exactly the same blade as the other ones, hence it might not be worth buying except when you have no other option.
Websites for Prop
Image Credit for Boat Propeller: Marine Prop Company, Utah, USA