Saturday, November 19, 2022

How Do I Find The Right Prop For My Boat

Family & Watersport Boats

How to choose right prop for your boat and motor

Reliance

The Reliance family of outboard props is also great for many family boats pulling towables and boaters who participate in watersports.

Talon Pontoon

Excellent low-speed operation, providing higher thrust and control than conventional propellers on pontoons using T50-F115 outboards. Features an SDS design that requires no special hardware to function.

Dual Thrust

Harnesses the power of Yamahas high-thrust outboards for pushing heavy loads such as sailboats and pontoons, and provides outstanding reverse thrust. Standard on T9.9 and T25, optional on T50 and T60.

Pros & Cons Of A 4 Or 3 Blade Prop

For us, if we go from a three blade to a four-blade without changing the diameter or pitch of the prop, we will lose top-end speed. What we will gain, however, is our hole shot .

Meaning we will be out of the water and cruising much quicker thanks to the extra blade generating a better grip from the prop to the water.

With the extra grip also comes better control and handling of our craft. Understanding these simple concepts is the crucial base foundation for us to begin the propping procedure to get the correct prop for your boat.

At the end of the day, it is ultimately up to you and what you are looking to get from your boat. Would you rather have a better hole shot or top-end speed?

Its your call! Personally, running larger boats close to the 30-foot range or higher calls for a 4 blade as its best for the size and weight of the boat. That extra blade really makes a notable difference in getting the boat out of the water and controlling it at higher speeds!

The Meaning Of The Numbers On A Prop

Typically, most propellers will have specific information engraved on them. This information usually consists of two to four sets of numbers and letters.

One being the propeller diameter, the second being the pitch length, third representing the rotational direction and fourth being the bore/shaft diameter.

An example of these numbers displayed resembles the following: 15.6 x 15 | RH | 1 ¼

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What About Shaft Size

The propellers shaft size is the size of the connecting shaft between the propeller and the boat. This is the only truly rigid aspect of choosing a propeller size your shaft size always has to remain the same.

If you were worried about the shaft size limiting your boats propeller options, dont be. Propeller diameters are made to fit shaft sizes, which are made to be big enough for their respective boats to handle.

A Few Important Definitions

First boat, first day, damaged prop. Safe to use? :(

Diameter: An important factor in thrust the larger the diameter of the prop , the more water that gets moved. As a general rule, when performance suffers, you change pitch and not diameter. Diameter is the first number listed in a prop size, such as 14 x 17.

Pitch and slippage: Pitch is the distance a prop moves through the water in one revolution. A prop with an 18-inch pitch would move 18 inches through a solid medium with each complete rotation. The reason a propeller moves less than 18 inches is because it operates in a liquid medium, which creates slippage. So instead of moving 18 inches, a propeller in water moves maybe 15 inches. Some slippage is essential. Without it, the prop couldn’t move the boat. But too much or too little slippage reduces efficiency. The second number stamped on the prop is pitch.

Rotation: Propellers can rotate to the right or the left . Most outboard and I/O propellers rotate to the right. Many sterndrives and even some newer outboards have two counter-rotating props.

Number of blades: More blades are smoother, but slightly less efficient. The typical compromise is three blades, although four blades are becoming increasingly more popular.

Thickness: Blades should be as thin as possible because it takes more power to turn a thick blade. Stainless propellers are five times stronger than aluminum, which is why they can be thinner and still retain adequate strength. Hence, stainless steel props are more efficient.

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Propeller Specifications Explained: Propeller Theory

Line A-B x 2 = propeller diameter

All propellers can be described in basic terms using a set of two numbers: diameter x pitch. Hence a prop with an 18in diameter and 12in pitch is described as 18 x 12. The diameter of the propeller is the circle which the tip of a single blade describes in a complete rotation. It is found by measuring from the centre of the propeller boss to the tip of one blade and then doubling the result.

How to measure the pitch of a propeller

Pitch is the forward distance that a propeller would theoretically travel in a single rotation if there were no slip present imagine a screw being driven into a piece of wood. The angle at which the propeller blades are set governs the distance travelled. A fine pitch gives a lesser distance than a coarse pitch .

A propeller is usually designed with two to five blades . In the first instance, the number of blades is decided by the weight of the vessel: the greater the weight, the greater the blade area required to push it through the water with a minimum of slip and cavitation.

To specify the correct type and size of propeller, a standard set of boat, engine and gearbox measurements is required. Designers will use the boats length, beam, draught and displacement in combination with the boats underwater drag characteristics to calculate hull resistance.

Should You Choose A Four

Three or four blades work well in either sterndrive or outboard applications. Three-blade designs give you all-around performance with an advantage on top end speed. Four-blade designs work well with boats that are difficult to get on plane, underpowered or used in watersports where top-end speed is not critical.

The composite cores of modular hubs are designed to break away upon significant prop strikes, helping to protect the prop body and engine drive train from damage.

Four blades in many cases will drop your rpm by 50 to 150rpm with identical pitch. Three-blade props are generally best for recreational boats with three-, four- and six-cylinder outboards and sterndrives, giving good hole shot and top-end performance.

The blades on three-blade props fill up about 50 to 55 percent of the available area inside the circle formed by the props diameter . Adding a fourth blade increases the DAR to between 60 and 65 percent, so you can expect more thrust to keep your boat planing at lower rpm, a potential boost in fuel economy, but also a reduction of 50100rpm at WOT.

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Should You Go With A Different Pitch

All marine propellers involve a tradeoff. If you prop your boat to maximize top speed, acceleration will be compromised and visa-versa. Therefore, the first consideration is whether to optimize top speed, acceleration or some combination of the two.

To increase acceleration, consider reducing your pitch. This makes particular sense if you are NOT hitting the max RPM level established by the engine manufacturer when running at Wide Open Throttle with your current prop. To see the potential impact on top speed, enter your current values for Max RPMs, Gear Ratio, Pitch and Prop Slip in the Boat Prop Calculator tool. Then, decrease the pitch by an inch or two. However, as you do this, you should increase your RPMs by approximately 200 for each 1 reduction in pitch .

Conversely, to increase top speed, consider increasing your pitch. This is especially relevant if you ARE hitting the max RPM level established by the engine manufacturer with your current prop. However, it is hard to tell whether your RPM level is the best your engine can do or if it is being capped by the engines rev-limiter . If it is the later, then you likely have room to improve your top speed. If it is the former, then it might not make much difference after you account for the fact that each 1 increase in pitch will result in approximately a 200 decrease in RPMs.

Final Notes About Sizing Your Rc Boat Propeller

How to Find the Size of a Boat Prop | How to Identify Prop Size | Prop Diameter and Pitch

The world of RC boating is a diverse one, especially when it comes to boat types, sizes, and shapes. Choosing a propeller is rarely, if ever, a cut-and-dry matter. If you are still feeling lost about your propeller sizing, keep these tips in mind:

  • Always check your engine temperature after a dry prop run. In RC boating, a heated engine is a soon-to-be-dead engine. The cooler your engine runs, the better off your little boat will be.
  • If you arent sure which propeller to choose for a race, test each out in waters similar to the type youll be racing in. This is the easiest way to ensure youll get the most accurate idea of how fast your boat can go.
  • Get experimental with it. A lot of RC enthusiasts find their favorite boat props by sampling a wide range of them until one or two just do the trick. Though simple, this approach is surprisingly successful at pairing boats to great prop sizes.
  • Different conditions will yield different results. Water temperatures, wind readings, and even the overall weather reading of your boats speed and water handling. This means that a propeller that performed great one day might not be ideal the next.
  • Never be afraid to ask for a little help. Every hobby has its own learning curve, and that includes RC vehicles. If you are feeling lost, ask someone for help. Even the boat kits manufacturers will be able to give you advice on where to start.

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How To Choose The Right Propeller

Let me start by saying, Ive been an avid boater all my life. Ive driven numerous different types of boats and have always been pleased with the propeller that was included from the factory every time.

If youre new to boating or dont have a strong opinion on the type of speed and performance youre getting out of the ride, then you might have the dealer recommend a prop or roll with what the boat manufacturer provides.

For instance, here at Barletta Boats, we try to find a middle ground prop that allows the motor to spin close to its max RPM. This way, youre getting a propeller that is made for your boat and will achieve near-peak performance without breaking the bank.

The traditional method of selecting a propeller takes the horsepower, boat weight, and hull type into account. Then the pitch and diameter are selected that allow the engine to run at the top end of the RPM range.

Once the boat is loaded with people and gear, this method typically provides good all-around performance. Some boaters may have different performance goals such as better hole shot or faster top-end speed, which will require a change in the pitch and diameter.

You generally want to find the comfort zone for props on your specific boat. If youre hitting the rev limiter, youve got too low of a pitch. Think of this as a 10-speed bike and youre going downhill on the highest gear.

Understanding A Boat’s Propeller Pitch

A boat propeller has two basic dimensions: diameter and pitch. These dimensions are used to describe the propeller, usually in inches, and always stated as diameter x pitch. For example, a propeller described as 14.5 x 19 has a diameter of 14.5 inches and a pitch of 19 inches. These dimensions are often stamped or cast right on the propeller. Recreational boat propellers are usually offered in two-inch pitch increments within a prop model line, but some high-performance props are offered in one-inch increments to allow for fine-tuning boat performance.

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Do All Boats Need A High Pitch Rc Propeller

Yes and no. Propellers with a higher pitch rating will travel further, but too much of a high pitch will eventually limit acceleration and speed. That being said, having a very low pitch prop on your boat can contribute to motor burnout. Its better to be safe than sorry in this matter.

Materials Used To Make Propellers:

Resources
Aluminum Propellers
  • 2 or more times the price of aluminum
  • 4 times more durable aluminum
  • Stiffer blades
3 Blade Propellers
  • Good for general purpose use
  • Slower to plane
  • Generally faster with higher top end speed
  • Available in many sizes
  • Better holding power in rough seas
  • Faster to plane the boat & keeps the boat on a plane at lower speed
  • Quicker acceleration with lower top end
  • Fewer sizes available

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What Problems Are You Looking To Solve

Is your boat sluggish coming out of the hole and slow to get on a plane? Are you not hitting the top speed you think you should? Do you want an improvement in fuel economy? Hoping for better all-around performance? Is your current prop blowing out or ventilating excessively in turns or when you accelerate? Are you looking to improve your boats watersports performance for tubing, skiing or wakeboarding? Once you have defined your goals, you can move on in the selection process.

Bass Bay & Flat Boats

V MAX SHO

An ultra-high-performance ventless design and single-inch pitches allow you to fine-tune the performance of Yamahas four-stroke V MAX SHO.

Pro Series

This stainless-steel series provides high performance for single-outboard boats requiring bow lift.

Talon SS4

Stronger hole-shot than comparable 3-blade propellers. Excellent on mid-range powered flats boats or for applications requiring high engine mounting heights. Fits F70 to VF115, T50/T60 K series gearcases. Standard Shift Dampener System .

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Is A 3 Or 4 Blade Prop Better

If we had a dollar for every customer support inquiry we receive asking whether a 3 or 4 blade prop is better, wed be giving away free boats! Its important to note, we are talking specifically about the average recreational boating and fishing application here.

This prop advice is not related to racing. Although the physics dont change, there are a ton of other variables to consider for racing that is not listed here.

What Determines The Type Of Propeller Your Boat Needs

How to Find Out if You Have the Right Propeller Pitch

If youre new to boating, you may not have expectations around what type of performance you should get out of your engine/propeller combo. That said, there are numerous variables behind which prop is right for your boat.

Propellers can make such an impact on performance that your neighbor could have the exact same boat and engine, but if the prop is different, the two boats could yield different results.

There are so many fluctuations and options that you could literally make the same exact boat faster just by adding a different propeller.

Choices that affect this change in performance are:

  • Stainless steel over aluminum
  • The pitch
  • Stainless is a stronger metal than aluminum, so this type of prop is tougher against damage. It also doesnt flex, so it holds its shape in the water and can increase the speed depending on boat and engine type.

    Aluminum is a softer and less expensive metal, so these props are usually more budget-friendly. That said, they do tend to flex, which can hinder the boats performance and speed.

    Other factors that make a difference in how your propeller performs are:

  • The boats weight
  • How the weight on board is distributed
  • The height of the motor
  • How the water comes off the hull
  • Choosing a propeller can be subjective depending on your performance goals, but different engines and hull designs do play into selecting the best prop.

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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.

    When Choosing The Right Propeller For Your Boat Youll Also Want To Consider The Material Used Number Of Blades And Pitch

    A lower pitch allows you to build up RPM quickly which is good for big boats with a heavy load.

    But there will be less forward travel with each revolution so not good for top speed.

    A higher pitch is slower to build up RPM resulting in lower pulling power and acceleration but a greater top speed once the vessel winds up.

    Youll also need to know how to read the prop. Meaning how to identify the size, diameter and pitch of a propeller.

    Most props have a series of numbers on the side or inside the hub.

    A three blade prop, 18.75 inches in diameter with a 19 inch pitch will have the numbers 3 X 18.75 X 19.

    Numbers are printed on the side of your prop tell you the number of blades, diameter and pitch of your prop.

    If they are not printed on the side of the prop, look for the numbers inside the hub of the propeller to determine diameter and pitch.

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