Thursday, June 30, 2022

What Boat Prop Do I Need

High Strength Or Low Strength

How to choose right prop for your boat and motor

Another characteristic of high-strength stainless is the fact that it shows more corrosion than low-strength stainless. This is a natural consequence of the higher carbon steel content used in the alloy. Low-strength stainless uses more nickel in the alloying combination. This provides a significant increase in corrosion resistance, but also drops the tensile strength, typically by 50% compared to the high-strength material.

The material used in low-strength stainless props is more similar to that used for deck hardware. Since the strength of the material is more like bronze than a high strength stainless, it will pretzel pretty easily. The good news is that it can normally be straightened out again.

In either case, the issue will be to examine for enough blade thickness to allow the repair to be completed and still have sufficient meat left for durability.

Proper propeller repair takes time and the right equipment.

You Want To Go Faster

In some cases, your propeller could be in good working condition, but youre still itching for a replacement.

Why?

You dream of jet-setting across the still water, catching stares and creating waves as you pass.

The only problem? Your current gear cant get you there. Instead, youre sputtering along, lagging behind your crew and making tiny ripples.

If this is true, go ahead and upgrade to a stainless steel propeller. Youll gain about two to three knots just by taking this step alone.

This is possible because aluminums innate strength means it can be thinner, which adds to its speed. Moreover, as youre cruising along, a stainless steel model wont lose its shape or flex too much.

Though youll spend about three times as much on an aluminum propeller, serious boaters know that the performance is worth the cost.

What Material Is Best

Most outboards and IOs are originally sold with aluminum props, which are inexpensive and repairable. Inboards use three- and four-bladed props of bronze, or a nickel-bronze-aluminum alloy. Replacement props for IO or outboard boats are available in aluminum or stainless steel. These materials compare as follows:

Aluminum is the most common, least expensive material. Suitable for most outboard and sterndrive applications.

Stainless steel offers a performance advantage over aluminum due to stiffer, thinner blades and more advanced designs. Best choice at speeds over 50mph, or if your boat is running over oyster beds or sandbars regularly. Stainless costs more but is five times more durable than aluminum. Stainless props can be repaired, at a higher cost, to like-new condition, while repaired aluminum will suffer from metal fatigue and a loss of strength.

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How To Calculate Propeller Pitch

Propeller diameter is simply the diameter of a circle scribed by the blade tips of the prop.

Propeller pitch is the distance the prop would move forward in one rotation if it were moving through a soft solidthink of a screw being turned into wood. The blades on a propeller are analogous to the threads on a screw. Some propellers have a constant pitch, meaning the pitch is the same at all points from the leading edge to the trailing edge of the prop blades.

Progressive pitch starts lower at the leading edge and increases to the trailing edge. The pitch number assigned to a progressive-pitch prop is the average across the entire blade. Progressive pitch improves performance in high-speed applications.

Propeller pitch determines the final gear ratio between the engine and the water. A boat should be propped to operate within its wide-open throttle , which can be found in the motor specifications or the owners manual. Ideally a motor with a WOT range of 5000-5800 RPM will reach 5400 rpm with the boat running wide open and trimmed out for optimal performance, with a full load of fuel and water and an average passenger load. That RPM may go up with a light load of fuel or passengers, and lower with a heavier loadby propping for the middle of the range there is leeway in either direction.

The best bet is compromise between these extremes, a prop size that puts the engine in the sweet spot of its RPM range for everyday use.

Stainless Steel Or Aluminum Prop How To Choose The Ideal Metal For Your Glasstream Prop

Do I need a new prop, or another boat?

To steel or not to steel, that is the question.

A question that has plagued Glasstream owners for decades. Which prop is better: stainless steel or aluminum?

Countless factors go into choosing boat props. They come in all shapes and sizes. Pitch, number of blades and branding are just the beginning. Throw in metal types into the mix and it just spells confusion.

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Aluminum Or Stainless Steel Prop

Another choice to make is choosing between aluminum and stainless-steel materials. Common with new package boats are aluminum props, which are inexpensive and repairable. Consider these differences when thinking of upgrading to stainless steel. Thinner blades and more advanced designs give stainless steel a performance edge over aluminum. Stainless costs more but is five times more durable than aluminum. Stainless props can be repaired, at a higher cost, to like-new condition, while repaired aluminum will suffer from metal fatigue and a loss of strength.

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It Doesnt Have Enough Pitch

Along the same lines, if your pitch is too low, your boat can overextend itself trying to catch up. As a rule of thumb, remember that the lower a propellers pitch, the higher its rotations per minute, or RPM. The higher its pitch, the lower the RPM.

If yours is still slow to pick up, even after over-revving, take it in for a pitch adjustment.

Its unwise to leave it in this condition for too long. Consider the long-term effects on your vehicle if you drove on the interstate in second gear.

While the rush of the speed is thrilling at first, it doesnt take long for the engine to experience major damage.

Is Your Engine Over Or Under Revving

The Correct Prop For Your Boat! How To Know!

Selecting the correct prop should result in your engine running within the designed rpm range at Wide Open Throttle . Your owners manual should include this specusually 50005500rpm for an outboard or 4200-5000rpm for a sterndriveor your mechanic or dealer may know. Allowing your engine to under rev or over rev at WOT can result in engine damage. Over revving or under revving can be corrected by selecting a prop with a different pitch.

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Right Hand Or Left Hand Rotation

A 4 blade propeller will usually have a smaller diameter for the same pitch size of the 3 blade equivalent. This is one reason they spin up quickly and yield good acceleration. The blades are often a bit smaller but offer more total blade area because of the additional blade, so they have more grip on the water. When switching from a 3 blade prop to a 4 blade, youll usually need to decrease the pitch by 1 or 2 inches to keep the engine RPM in the same range.

How To Find Your Best Propeller

The Prop on the Boat Goes Round and Round

Propellers are the final gear in your boats driveline. Having the correct prop on your boat can make the difference between happy boating and costly floating. Because props come in a huge variety of shapes and sizes it can be a tricky task to identify the one that works best on your boat. Here are the steps that I recommend to both find your propeller and understand how it works.

Information gathering is the first step in finding your best prop. This includes the make, model and year of your boat and engine. Also note the make and size of your present prop . Then consider how you use your boat. Is it for family day trips, long cruises, or tow sports? Finally, record the maximum RPMs that you can achieve with your existing prop at wide open throttle.

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Brave New Blade Design

With modern propeller design and construction methods the three main criteria are no longer the only governing factors. Increasingly, shape is just as important.

If the diameter needs to be smaller to provide better acceleration then the blade area can be increased by adding more blades. For optimum performance, fuel economy, fast acceleration and smooth vibration-free running, it is the shape and cross section of the blades that make the crucial difference.

For the everyday boat owner blade shape is governed by the boats dimensions, its engine specifications and the owners choice of propeller manufacturer. High-tech computer-designed and machined propellers only become viable for yachts over 24m where the shape of the blades is tailored to the requirements of the vessel taking into account resistance as well as all the normal information required to build a propeller.

This Sunseeker propeller is a good example of what is required to propel a heavy high-performance craft. The total area is greatly increased by overlapping the leading and trailing edges of the blades. This avoids the problem of cavitation, but the blades are shaped to ensure water flows smoothly through the propeller

The shape of the older equipoise is reminiscent of the latest foil design although it has less blade area.

The round blade turbine propeller is still used on heavy displacement craft including commercial vessels. It has a large blade area and thick sections to resist damage.

How To Determine Boat Prop Size

Prop and Skeg Damage
  • Measuring tape

  • Calculator

A boat’s propeller has two numbers that relate to its diameter and pitch. If a prop has a diameter of 12 inches and a pitch of 23 inches, for example, it’s called a “12/23” prop. Most props have this information inscribed on the hub, but use or wear can render the inscription unreadable. Still, obtaining this information is a process even a novice mariner can perform.

Measure the distance from the center of the propeller hub to the outermost point on one of the propeller blades. This measurement represents the radius of the propeller. The first number used in describing a propeller is the diameter of the circle described by the propeller, which is twice the radius. Hence, a propeller that measures 6 inches from the center of the hub to the outermost point on any one of the propeller blades has a diameter of 12 inches.

Determine the pitch of the prop by observing the performance of the boat on the water at half-speed, taking note of the indicated speed and the number of RPMs indicated on the boat’s tachometer. The pitch of a prop is the distance, in inches, one revolution of the prop will move the boat forward. Any calculation of a propeller’s pitch is approximate, since the actual performance of a propeller is affected by factors such as hull shape, water salinity, cleanliness of the external hull surfaces, air and water temperature and water depth.

Tips

References

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    Stainless Steel Boat Props

    SS is identical to aluminum when it comes to styles. However, a majority of SS props do not use a hubless design. That means you are stuck with a hub that is pressed in. Or, in other words, Prop A will not work with Motor B.

    The Cost of Stainless Steel Props

    As mentioned, youre going to pay a pretty penny for a stainless-steel prop. The question is why pay the extra money?

    The typical SS prop repair ranges from $140 $250. Yes, stainless steel is more expensive to repair, but its also worth the effort compared to aluminum. Youll repair SS over buying a new one, because repairs are hundreds of dollars less than buying new.

    Life Expectancy of Stainless Steel Props

    SS props have a much longer life expectancy. Theyre durable and stronger than aluminum props. They also dont experience flexing. Since aluminum is softer than SS, when its under load and rotating thousands of times a minute, it loses its pitch. What we mean by that is the blades under a load will move and negatively, affecting your performance. SS holds a more true pitch, which gives you better performance and even better fuel economy.

    Think of it this way: Aluminum is like a car with a funny transmission that sometimes slips or shifts hard. SS is like a fine-tuned performance car that shifts effortlessly and doesnt slip when put into gear.

    Pros and Cons for Aluminum and Stainless Steel Props

    Aluminum Pros:

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    How Do You Choose The Right Sized Propellers For Your Rc Boat

    Its important to remember that there is not one perfect size for an RC boat propeller. What size works for your RC boat will depend on a variety of factors, including the following:

    • Motor Strength
    • Diameter
    • Shaft Size

    Most top RC boating experts calculate the best size for their RC propellers by finding the total pitch of their potential prop. This calculates how far the boat should go after one full turn of the propeller. The higher the total pitch, the faster the boat will go.

    Are You Under Or Over Revving The Engine

    Prop Replacement How-To | BoatUS

    Your boat owners manual will include specs that tell you within which range your boat engine was designed to rev. Itll look something like this: 4200-5000rpm for sterndrive or 50005500rpm for an outboard.

    Under revving or over-revving, your engine will damage it faster than you would like. If you find that your boat engine is either under revving or over-revving in contradiction to the specs, the simplest solution is to buy a propeller with the appropriate pitch for your specific boat, which leads us to the next point.

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    How Do I Know What Pitch Prop I Need

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    A 3 blade propeller usually offers top speed performance while a 4 blade propeller provides maximum thrust and smooth cruising operation. Four blades have some features of their own, though. They often provide more lift at the stern which will help accelerate the hull, especially if it is stern heavy.

    Similarly, what do Prop numbers mean? Numbers Stamped on the Propeller.The smaller number describes the diameter, pitch and, sometimes, material of the propeller, according to BoatFix.com. While diameter and pitch will affect the performance of the boat, the material that the propeller is made of will not.

    Subsequently, one may also ask, what is the difference between a 17 and 19 pitch prop?

    The 17prop will give you a better hole shot but lower top speed. If it is to small it the engine may go over the recomended top RPMs. The 19prop will give you less of a hole shot but a higher top speed if the motor is strong enough to turn it in the recomended top RPM range.

    What prop pitch is faster?

    Pitch is the distance the propeller will move the boat after one revolution . A lower pitched propeller will create more power due to more engine RPMs, but the boat will move slower. A higher pitched prop allows the boat to move faster by travelling a farther distance with each rotation.

    How To Select A Propeller For Your Boat

    Selecting the right boat propeller is an important factor in maximizing your boat’s performance. Determining the correct size and style of boat prop will keep the engine operating within its recommended RPM range and allow it to apply its maximum horsepower to the water. One of our goals at Overton’s is to help make choosing a boat propeller an easy process. We have a huge selection of props and prop accessories at great prices! Optimize your performance with the right propeller using the information below or take advantage of our propeller selector tool for help in choosing your prop.

    MATERIAL – We offer propellers made of composite, aluminum, and stainless steel. Composite props offer good performance, are durable, and inexpensive. They also offer some protection for your lower unit during a prop strike. Aluminum props are the most common and are suitable for the widest range of applications since there are so many models and styles available. Stainless steel props offer the highest performance and best durability.

    Select the prop size that lets your engine operate at WOT in the correct RPM range.

    NUMBER OF BLADES – When the number of blades are changed, diameter and pitch may require adjusting to keep the RPMs in the proper range. For most purposes, 3 and 4-blade boat propellers can be used interchangeably on outboards and sterndrives without much of a change in performance.

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