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What Size Prop Do I Need For My Boat

How Does Prop Diameter Help Or Hurt Performance

How to choose right prop for your boat and motor

Re: how does prop diameter help or hurt performance?View Full ProfileRE: how does prop diameter help or hurt performance?

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RE: how does prop diameter help or hurt performance?Jerry-Rigged – 11/28/2006 6:19 PMLarger prop has more surface area. The extra surface area does two things – 1-gives the prop more thrust, and 2, gives the prop more drag.More thrust means for a big heavy boat may get on a plane easer with less power. More drag means you won’t be able to turn it as fast, so you will need to drop the pitch a bit Also, at lower speeds, it is more effecent to spin a big prop slower, than to spin a small prop faster .High speed boats use small props.Slower planing boats use props a bit bigger.Displacment boats use big’ol props.JerryRe: how does prop diameter help or hurt performance?Re: how does prop diameter help or hurt performance?Re: how does prop diameter help or hurt performance?Re: how does prop diameter help or hurt performance?Re: how does prop diameter help or hurt performance?Re: how does prop diameter help or hurt performance?Re: how does prop diameter help or hurt performance?Re: how does prop diameter help or hurt performance?RE: how does prop diameter help or hurt performance?

Comparison Test: Boat Props

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Each year, hundreds of boaters spend countless thousands of dollars on machine-shop equipment and bolt-on gadgets in their quest to increase outboard horsepower. Yet the easiest and least expensive way to improve performance is to change propellers. Regardless of your rig’s size, horsepower or application, the right prop can make the difference, whether you seek increased speed, better handling or more power.

Even if you’re happy with your boat’s performance, you and your family might participate in more than one watersport, and you may benefit from changing props. Fishing, cruising and waterskiing all place special demands and different loads on your engine. Choosing a prop with the correct pitch, diameter, rake, surface area and contour will keep your engine within factory-recommended wide-open throttle rpm ratings. Besides, having more than one prop on board is cheap insurance and good common sense.

Whether you’re interested in props with names like “chopper” or “cleaver,” or if you just want to know the differences between sizes, materials and trade names, your dealer’s an expert. But PM wanted to go beyond theory and show how different props can change boat performance, so we tested six props that incorporate a variety of materials and designs, from the most basic to the technologically advanced.

Basic properties

Material matters

five times stronger, making them desirable




Size Prop Do I Need My Boat

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Choosing The Right Propeller By Crowley Marine

The right prop will get the best performance out of your boat. Matching the propeller to your application, whether cruising, water skiing or performance, maximizes the power from your engine. It also helps with handling and acceleration. Use this guide to learn how different propeller designs affect efficiency, power, and speed and then learn how to choose the correct prop for your boat and application.

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

Steel or Aluminum Prop? What I Use and Why

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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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

The Basic Parts Of A Prop

1. The Blade Tip The extreme end of the blade.

2. The Leading Edge The part of the blade that cuts the water.

3. The Trailing Edge The part of the blade where the water leaves.

4. The Cup of the Blade This is the curve in the trailing edge of the prop blade that extends from the hub to the tip. It adds pitch to the blade.

5. The Blade Face That part of the blade that faces aft and is the positive pressure surface.

6. The Blade Back The part of the blade facing forward that is the negative pressure surface of the prop.

7. The Propeller Hub This is the metal base to which the blades are attached. On stern drive and outboard boats there will be an inner and outer hub. The inner and outer hubs are connected by thin ribs of metal or rubber with splines connecting the hub to the drive shaft. Both the metal ribs and the rubber are designed to protect the gears in the lower unit in case of grounding under power.

Stainless steel props are expensive but very durable.

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Should You Pitch Up Or Pitch Down

Engine rpms and pitch are inversely related. Increasing the pitch will decrease engine rpms and decreasing the pitch will increase engine rpms. As a general rule, a two-inch increase in pitch will result in a reduction of 300 to 400 rpm. Conversely, a two-inch decrease in pitch will result in an increase of 300 to 400 rpm. Going back to the question of performance at WOT, if your engine is under revving, consider a propeller with less pitch. If your engine is over revving, consider a propeller with more pitch.

Is A 3 Or 4 Blade Prop Better

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

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.

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Boat Propeller Fit Guide

If you’re buying a new propeller for your boat, you may simply need a replacement for a prop you damaged, you may be trying to address a performance issue or you may simply want to gain better fuel economy. Whichever the case, we can help you find the right propeller for your needs.

Choosing the best propeller for your boat is a key factor in performance and choosing the wrong prop can lead to poor fuel efficiency and issues with engine performance including slower speed and increased wear and tear on your engine.

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.

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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.

Selecting The Yamaha Propeller Thats Best For You

Broke Skeg

Are you looking to replace or upgrade your Yamaha propeller? Our Outboard Propellers Engineered for Performance article covered the basic engineering characteristics of a propeller. Even a casual reading will allow you to conclude that every inch and angleeven its materialmakes a difference in the way your Yamaha propeller influences your boats performance.

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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.

Choosing Prop Pitch For Your Application

Each engine manufacturer has preordained the WOT rpm of your engine and usually the pitch of the prop fitted to that engine will allow it to reach that rpm setting. If the engine cannot reach the intended WOT rpm, and if the engine is performing properly, it probably means that the prop has too great a pitch. A prop expert can suggest what pitch prop you should have based on the performance of your boat in relation to its factory-rated WOT rpm.

Changing the pitch of your prop will change the boat’s performance. Think of it in terms of a manual-shift car: the lower the gear, the easier it is to turn high rpms. Likewise with a prop, the lower the pitch, the easier it is to turn high rpms. In a car or truck if you are trying to go up a hill with a heavy load, the transmission must be downshifted into a lower gear making it easier for the engine to turn the rpms it needs to move the weight. The same is true in boats.

If you want a fast hole shot for water skiing or another purpose such as a bass tournament start, then you may want to lower the pitch of your prop. Also, if you plan on running your boat heavy because of the number of passengers or equipment aboard, you should consider lowering the pitch of your prop.

If you discover that you have purchased an under-powered boat, buying a prop with a lower pitch could be the least costly solution to your problem.

Cup size is important. It affects speed, fuel consumption, and WOT speed.

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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.

Its Also Important To Note The Details Regarding Trimming Up During This Process

The Correct Prop For Your Boat! How To Know!

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!

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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.

What Is Hull Resistance

Resistance is the hulls natural tendency to drag through the water. Bare hull resistance is produced by skin friction of the hulls surface, waves created by the hull running through the water and the shape of the hull below the water. To the bare hull, the drag of appendages must be added such as rudders, shaft support brackets, shafts, depth sounder transducers, stabiliser fins, etc. However, the design of the lift surfaces of the hull also have a very significant effect. Designers work to ensure that the lifting characteristics give the hull the least resistance at normal operating speed.

Once this resistance is known, engine and gearbox specifications can be combined with maximum propeller diameter to determine the props minimum requirements. The vessels duty cycle, which is simply a judgement as to whether a boat is to be used for heavy or light commercial or pleasure purposes, then also influences a designers final specification.

Propeller diameter is first decided by the type of boat. A large-diameter slow-revving propeller is the most efficient type but this wont provide the necessary acceleration to get a sports cruiser onto the plane. Acceleration is achieved by increasing the rotation speed, which usually means a smaller diameter propeller. The fact that many modern sports cruisers have limited propeller clearance space is another reason for fitting smaller diameter propellers.

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Boat Prop Selector Guide

Whether you are buying a new propeller for your boat, simply in need of a replacement for a prop you lost/damaged, trying to address a performance issue or you simply want to gain better fuel economy, we can help you find the perfect propeller for all of your boating needs. Propeller Depot offers the best pricing in the marine industry on all inboard, outboard, ski/wake and stern drive propellers. Order your boat propeller today from Propeller Depot and save.

Find A Replacement By Oem Part Number

propeller 85hp yamaha racing

If you know the OEM part number and basically just need to find the replacement, use the Prop Finder tool. Or search the pages and PDF guides below by your OEM part number to find a suitable replacement. Give us a call at 1-800-998-9508 or Intl. +1-206-780-5670 if you don’t find what you need and our boating experts will quickly help you locate a replacement.

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Do Your Props Have The Right Cup Rake Slip Pitch And Hub

The more we research some subjects, the more we discover that some of the assumptions we have operated on for years are not correct. There is probably no field in the boating world that is more of a black art, or is subject to more misinformation than in re-propping.

Getting the right prop is not really a matter of voodoo. It’s more a matter of finding out there is a prop problem in the first place, rather than a matter of finding an expert you can trust who can recommend what you need. We hit the important basics and examine some alternatives in this short report on prop basics.

You might not be able to do anything about your boat or engine, but you certainly can do something about your props. Are you really sure you’ve got the right wheels?

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