Pitch Prop Vs 19 Pitch Prop: Which Do You Need
by Kyle WUpdated on April 23, 2021.
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Your boat is very much like your car without proper maintenance and the right parts, it will give you issues and might leave you stranded while out fishing for bass. The difference between your boat and your car is that the parts arent quite the same.
While it will do you well to know how to change a flat on your car, when it comes to boating, propeller diameter and pitch are some of the most important terminologies. This is because its your propeller that actually drives the boat. So understanding a bit about it could save you a whole lot of headache down the road.
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Choosing The Right Propeller For You Boat Requires Trial And Error
Often, your dealer can supply two or three props for testing when you buy a new motor for a small fee.
This is because boat design, load and the running characteristics of your vessel all play a part.
Watch our video as we chat to marine mechanic Matt Solis from Barneyss Marine Hervey Bay for some tips and considerations when choosing the right propeller for your boat.
Ryan Moody
Ryan Moody started his fishing career on the reef boats before catching bucket list marlin for the likes of champion heavy tackle angler Johnno Johnson, INXS and the King of Sweden. Branching out in the late 80’s to guided barramundi fishing, Ryan has made a name for himself as a Big Barramundi specialist and to date has put clients onto over 2000 metre plus barra. That is over 2 kilometres of metre plus barra! With attitudes changing from ‘keep all you can’ towards catch and release, Ryan has decided to share his extensive knowledge and hopefully inspire people of all ages to get out from behind the computer screen/TV and into the fishing outdoors lifestyle he has spent his life perfecting.
How Does A Boat Propeller Work
Lets first breakdown how a boat propeller functions to better understand why its important to choose the right one for your boat.
Although propeller theory is straightforward, there are a few variables behind what makes it spin. A propeller displaces water and creates thrust by rotating its blades.
The angle at which those blades are placed relative to the hub is called pitch. The pitch of the propeller will dictate how far it moves with each thrust.
Pitch is calculated by the theory that if a 12 pitch propeller is moving through a solid structure, one revolutionor turnof the propeller will move it forward 12 inches. This is what happens when a screw moves through a solid such as wood.
So, if the propeller pitch is 16 inches, it will move 16 inches. The more pitch you are trying to turn, the more torque is required from the engine.
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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.
Pitch Vs 19 Pitch Prop
Again, we want to make sure that you are really understanding the foundational principles of propping your boat. The only way to determine the correct prop is through good ol trial and error.
Swapping and testing different props until you identify the sweet spot in relation to your RPM range and limiter setting.
Each engine has a specific top-end wide open throttle RPM range. Each engine manufactured in the last 20 years will also have the rev limiter .
If we put a small diameter prop on an engine with a low pitch. What will most likely happen is the power of the engine will overpower the ability of the propeller.
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A Few Important Definitions
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.
What Does Prop Pitch Mean
Propeller pitch typically referred to as prop pitch, is essentially the distance a propeller would move in a single revolution through soft solid. Kind of like the distance a screw would move through wood in one rotation. So, in this case, a 21 pitch prop would move 21 inches forward in one revolution, and a 19 pitch prop would move 19 inches forward in one revolution.
So what does all this mean to your boat?
Think of your propeller as if it were the axle on your car. The lower the ratio, the more pulling power it has from a standstill. This is the same physics that is applied to a boat propeller. A boat with a lower pitch propeller could accelerate much faster from a standstill position than one with a higher pitch propeller. Unfortunately, this lower pitch would make your engine reach maximum rpm at much slower speeds, albeit faster acceleration.
On the other hand, a higher pitch propeller will give you better top speeds but much slower acceleration. It should also be noted that simply fitting a high pitch propeller to a boat with a lower horsepower engine doesnt mean that you will make your boat faster.
While the boat will achieve higher speeds, it will do so for a short while before getting bogged down. The propellers higher pitch and diameter will eventually overwork and wear down the internal engine parts that just arent built to withstand that kind of stress.
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Learning About Boat Kit Propeller Compatibility
If you are relatively new to the world of RC boating, then all this talk about math, propeller testing, and engine burnout can be intimidating. After all, hobbies are supposed to be easy, right? Not a problem. There are some easy ways to handle finding new propellers for your boat:
- Check out the name, make, and model of your RC boat kit. Boat kits made by major manufacturers are fairly popular and well-known in the RC world. In some cases, propeller makers will mention some of the more popular kits their props are compatible with.
- Poke around online RC boating forums. The RC boating community is one thats extremely supportive and open to helping newbies. Going onto online forums and asking for help as a newbie is a great way to get suggestions on propeller sizing for your boat.
- Its also totally okay to read reviews on propeller add-ons made for your RC boat kit. If your kit is extremely popular, you might find reviews that offer advice on propellers that are made with your kit in mind. Picking those propellers, or even just finding ones with similar measurements, is a good way to get great results.
- Read your boat kits pamphlet. Some boat kits come with pamphlets that offer guidance on propeller sizing, as well as information about the best propeller material for your boat to use. Heres hoping you didnt throw out that pamphlet!
Maximizing Horsepower Minimizing Rpm
The right propeller for your boat and engine combination is based in part on the wide-open throttle operating range for your specific engine. This information is an intersection of horsepower and RPM and can be found in your owners manual.
An optimal outboard propeller will maximize your boats performance while allowing your engine to operate in the recommended RPM range. The correct propeller will prevent the engine from over-revving and facilitate maximum horsepower with minimum RPM.
An outboard engine under load should reach the manufacturers recommended RPM at WOT, usually expressed as an RPM range. Your optimal propeller will deliver acceptable acceleration and top speed while still allowing your Yamaha outboard to reach its recommended revs at WOT.
If you get this relationship wrong, premature engine damage is too often the result.
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How Long Does A Propeller Last
Like with anything, if you take care of your propeller, it should last the lifetime of your boat. Props do not have an expiration date as long as they arent damaged from impacts with foreign objects.
This is where knowing how to trim the engine is critical. To trim the engine simply means moving the engine up and down by using the trim function typically found on the throttle.
If youre in a shallow area, trim the engine up to avoid hitting the propeller on inanimate objects like rocks and lake debris. In deeper spots, you can trim the engine down without the threat of propeller damage.
Small nicks and dings on the blades are usually no cause for concern, but larger damages should always be inspected by your dealer and either repaired or replaced.
If you find that the boat has lost acceleration, top-end speed, and has any vibrations that are abnormal, it could be a sign that you need to take a closer look at the prop.
How Does Propeller Diameter Factor Into Your Ideal Size
The size of a propellers actual diameter will change the way your RC boat handles the water. Heres what you need to know about diameter sizing:
- The typical standard size for an RC boat propeller is between 65 to 80 mm for a gas-powered boat. If your RC boat is around the average size and weight, this diameter will work well for you.
- Heavier boats need larger propellers. Larger, heavier boats will need more prop to push them through the water. Its just physics! A larger propeller will give more force to push the boat.
- Remember to start small and test propellers out. If you arent sure how large a prop your RC boat can take, dont worry. Test out your boats motors for 20 to 30 seconds with a potential propeller, then wait 5 seconds. Gently touch it. If its too hot to touch, you need a smaller propeller because the motor cant handle it.
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Its Also Important To Note The Details Regarding Trimming Up During This Process
Normally you wont have the boat fully loaded when propping it out.
Its best to prop it out towards the top end of the RPM range without trimming the engine. We want to be able to add some trim to the engine and come really close to hitting the rev limiter under these conditions.
This is because whenever we load the boat up and take it out under normal conditions. There will still be room to add some trim at wide-open throttle and have the RPMs come all the way up to the top of the RPM range.
If we have to trim up the engine to get to the top of the range, then after we load the boat. We wont be able to get to the top of the range because of the additional weight that has been added to the boat.
Thats all for now folks! Now that you have a better idea of how to correctly prop your boat for the best results. Remember to share this article with a fellow boater! We also encourage you to check out one of these other helpful articles that we have written!
Finding The Right Outboard Propellers For Your Boat
When you are shopping for high performance outboard boat propellers it is important to do your homework so you choose the right replacement for your old propeller. If you fail to choose the right propeller you will not improve your boat’s performance on the water. You will need to consider size, style, and material when you are comparing all of the different top name brands on the market today. Understand how to determine which size and style is best for your boat and make the best investment of your hard-earned money. The biggest key is finding the propellers that will fit your engine, you can use the Propeller Guide at Propeller Depot to provide this list. If you have any questions in terms of which propeller you need, email or call the experts at Propeller Depot.
Prop Size and What to Consider
You may already know that not all boat propellers are the same. Understanding how they differ in size in important. Prop sizes refer to the diameter or the propeller and its pitch. Boat propellers with smaller diameters are meant for smaller board with smaller engines. As you might assume, larger propellers are designed for maneuvering larger boats. Pitch means how much the boat will move in one revolution. If you purchase a propeller with a higher pitch your boat will move faster as long as the engine is powerful enough to keep the RPMs in the right range.
Number of Blades
Which Material is Best
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Selecting The Best Prop Is Crucial But Easy With Mercury Marine
Boat dealers and service experts will tell you that incorrect prop selection is a leading cause of poor engine and boat performance. The Mercury Propeller Selector tool on MercuryMarine.com helps boaters select the best propeller model and pitch for their boat. The Prop Selector is essentially a digital catalog that aids in selecting the most appropriate propeller.
To find your propeller on MercuryMarine.com, click on Propellers, then click on Mercury Prop Selector. Once there, follow the simple steps to select your boat type, boat usage and engine information, and the Selector will provide a recommended prop family. The Selector then helps you determine the correct pitch of your propeller.
To find your closest Mercury dealer for assistance in selecting the best propeller for your boat, click on Find A Dealer on MercuryMarine.com and follow the easy steps.
PROP SELECTOR Q & A
What does the Prop Selector do?
The Mercury prop selector asks the questions that a typical prop guy will ask when someone says they need a new prop for their boat. The tool uses that information to provide a good starting point for prop selection based on your input on boat type, type of use, engine/drive type, etc. Just like working with a prop expert if you have existing performance data, the tool can also take that into account and be more accurate with its selection .
How does the Prop Selector benefit boaters?
The prop selector works equally well for all types of boats.
What Is Propeller Diameter And Why Does It Matter
Any time you want to buy a new propeller for your boat, you need to understand what the specs are and what all those terminologies mean. Propeller diameter and pitch are two of the most important specifications that directly translate into real-world performance.
Lets start by defining what they mean.
The diameter of a propeller is the distance across the full circle being made by the blade tips. Its primarily determined by the rpm at which the propeller would be turning as well as the amount of power being delivered to it. This diameter tends to increase on propellers typically used on slower boats while increasing propellers used for faster boats.
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