engine that looks like a bowl of metal granola inside.
Props also typically come with either 3 or 4 blades. Without getting into the hydrodynamics (yawn) – a three bladed prop gives you a little bit higher end speed, it’s slower to plane, there are usually more pitch and style options and they are typically cheaper than 4 bladed props. Conversely the four blades will give you a faster hole shot and reportedly better performance and fuel economy at mid-range rpms, better holding power in rough water and bet- ter low speed handling.
Choosing between aluminum or a stainless prop isn’t too difficult as long as you understand yourself and your budget. Aluminum is cheaper – cheaper to buy and cheaper to repair (providing you don’t damage it too often) and in a classic case of ‘you get what you pay for’ – worse performance.
My suggestion is you buy both. Use the stainless prop as your main prop - pick the pitch, diameter and number of blades for the way you boat most of the time. Invest in an aluminum prop for your other style of boating and keep it as a back-up on the boat. Think about it. If you damage your prop and it ends your day – sunshine, boat full friends and family on vacation – add in the cost of the repair and you will be truly miser- able. If you can salvage the day with a back-up prop it will be a lot less painful.
Modular Composite Props The concept is simple. Have removable blades attached to the hub so that in the event of a prop strike you simply replace the damaged blade from your spare set. You can also purchase blades
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with a different pitch – swap out the blades instead of the whole prop. The blades are typically composite which means that they can’t be repaired only replaced. Performance is slightly below the best stainless steel props but the cost to purchase and repair are lower.
Essentially they make a good perfor- mance upgrade from aluminum props without the expensive of going to stain- less.
Replacing Your Prop If you’re happy with your boat’s perfor- mance, get a prop with a similar pitch and diameter. Maybe upgrade to stain- less or go with 4 blades. If the old blade is salvageable – get it repaired and keep it as a spare.
If you’re not happy with the perfor- mance, change it. Rpm and pitch have an inverse relationship (sounds like a marriage). If you increase pitch, you decrease rpm and conversely if you decrease pitch you increase the rpm. Let’s try this out in an example. Imagine you have an outboard and your redline is 5300 rpm. At WOT, your engine revs at 4900 rpm. Since a change of 1” pitch usually changes your engine speed by 200 rpm, you buy a prop with 2” less pitch to bring your rpm at WOT to just 100 rpm shy of redline. In this case, you should get more acceleration and odds are your top end speed will stay the same (maybe get better) since your en- gine kicks out more horsepower closer to redline.
If you have specific questions about your particular boat or prop, visit your local qualified boat dealer or marine repair centre and get the best props for you and your boat.
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