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Sail-World.com : Your Propeller - the unsung hero of boating
Your Propeller - the unsung hero of boating
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'Manufacturing of the unsung hero - an incredibly complicated process'
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The importance of the propeller, whether on dinghy, sailing boat or speedboat, and the vital care necessary to keep it 'tuned', is brought home in this informative article by Canadian Yachting:
Doesn't a propeller look simple? Visually, the size and shape makes it obvious that a propeller kind of 'screws' its way through the water and to a casual observer, it looks to be one of the simplest parts on the whole boat.
Well, it’s exactly the opposite. Your propeller is the unsung hero of boating. It’s probably the single most complex
piece of engineering on the boat. The size and shape of the blades and their angle to the hub are just the start of the story.
The thickness of the blades, the rake and angle of attack at various points along its length, the finishing of the blade edge, whether or not it has any 'cup'. These are all factors and there are many more. Change just one and the performance changes.
Two miles per hour; that’s what we lost when we accidentally backed out a little too far in a motor boat and at idle speed but in gear; our prop blades just kissed the edge of a rock.
After that, the GPS revealed that the boat was running 35.7, not the previous 38 mph. We still got the maximum revs too…just not the speed.
We put the boat on the trailer and looked at the propeller. At first glance, the prop looked to be OK. Expert examination showed that it was out of 'index'. Index is the space between the blades.
 | Propeller manufacture -just a small part of the process - .. . |
Our almost unnoticeable accident could also have put the prop out of 'track'. Track is the relative height of each point. Sometimes a propeller strike bends all blades equally. The GPS does not lie though. We immediately lost 2 mph off the top speed.
Even minor prop damage can set up a noticeable vibration at various speeds that can cause future damage to gears, seals and drive train parts. Of course, performance and fuel economy can suffer too!
Luckily, there’s a great solution to this and it’s cheap – some-times even free, and you can do it this winter when your boat is in not in use.
The winter time is the perfect opportunity for you or your marina to remove your prop and have it checked out. Often, there’s only a nominal charge for a prop check that could reveal damage that could be costing you lost speed, wasted fuel, or excess engine vibration.
Many props can be 'tuned' or repaired for minor damage, being out of index, or out of track. If a blade is nicked,
bent or cracked, it may be possible to repair it and if the prop is badly damaged, you should just replace it anyway.
Props are not inexpensive (although repairs are quite affordable) because they are actually quite tricky to make. They are even harder to design but that’s for another article!
by Canadian Yachting
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9:06 AM Tue 19 Jan 2010 GMT
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