Thursday, May 16, 2024

What Size Propeller For My Boat

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

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

What Are The Problems You Are Looking To Solve

What are some of the issues you are facing?

  • Is your boat sluggish when coming out of the hole, or are you having issues hitting the kind of speeds you want?
  • Is it a fuel consumption issue?
  • Do you want better all-around performance?
  • Maybe your current prop is ventilating excessively?

As soon as you define the problem, you will be in a much better position to find the perfect solution.

Does My Boat Have The Wrong Size Prop

If the boat is over-propped the engine will not reach maximum rpm and the boat will underperform. Equally, if a boat is under-propped and the engine easily reaches or exceeds maximum rpm, the propeller needs more bite to get the boat to maximum performance level.

With outdrives, adjusting the pitch of the prop is often the only option, as the maximum diameter propeller is often already installed. Increasing the pitch will decrease the revs and vice-versa. If the engine revs seem OK with the current prop, but you want better acceleration, it is often possible to reduce the diameter and increase the pitch by roughly the same amount to give added acceleration without losing the top-end speed.

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Family & Watersport Boats


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.

Choosing The Correct Propeller Will Give You The Best Of All Worlds For Performance Sailing Club Racing Motor Sailing Or Motoring

Rx4 (15 x 25" ) EVINRUDE® JOHNSON® RH Propeller, 177328 ...

Should you ditch your fixed propeller? If your goal is to sail or motor to your destination more quickly, whether to the anchorage for cocktails or to your first waypoint on a passage, then a folding or feathering propeller delivers just that – less drag than all fixed propellers.

The average boat equipped with a folding or feathering propeller will gain between 0.75 to 1.5 knots of boat speed under sail over a boat with a fixed-blade propeller. In the folded or feathered position your boat will steer better and point higher due to unobstructed water flow to the rudder.

Many sailors often say We do not race, we do not need a folding or feathering propeller. But once they have seen equal sized boats passing them, they will consider this upgrade in order to sail and motor faster with the added benefit of 100% reverse thrust.

Investment Comparison

What is the extent of your winter budget, and what other investments for your boat are you considering? If you had the option to purchase a new genoa for the same price as a folding or feathering propeller, ask yourself the following questions:

  • Will it increase your sailing speeds by approx. 1.0+ knots?
  • Will it allow you to go to windward better in all conditions from flat calm to heavy winds?
  • Will it maintain this performance over 10 or 15 years?
  • Will it improve your backing down and manoeuvring?
  • Will it increase your fuel economy and therefore increase your cruising range?

How do they work?

What to look for

Blade Shape


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Are You Under Or Over Revving The Engine

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.

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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Stainless Steel Vs Aluminum

Its a question of strength and performance. Aluminum propellers usually cost quite a bit less, however, stainless steel is over five times more durable than aluminum. If youre looking for quicker acceleration, superior top speed, or better overall performance, you should consider a stainless steel propeller.

Aluminum propellers arent expensive, they work well, and are relatively easy to repair, but aluminum isnt particularly durable, making aluminum props susceptible to wear and damage.

Stainless steel propellers cost more up front however, because stainless steel is stronger than aluminum, a stainless propellers blades are usually thinner and can be made in a wider variety of styles and shapes than an aluminum prop, thus the potential for better performance and increased service life.

Remember, it is stain-less steel, not stain-proof – a stainless propeller can still rust, so you need to keep it clean, just like the rest of your boat.

Three Blades vs Four Blades

Four blade propellers usually:

  • Plane the boat faster than 3-blade propellers.
  • Keep the boat on plane at a lower speed.
  • Give improved mid-range speed at the same RPM as a 3-blade propeller.
  • Provide quicker acceleration than most 3-blade propellers.
  • Run smoother than 3-blade propellers.
  • Have better holding power in rough conditions.
  • Are less likely to ventilate in sharp turns.
  • Provide better low speed handling.
  • Are not quite as fast on the top end as a comparable 3-blade propeller.

How To Calculate Propeller Pitch

How to Choose the Right Boat Propeller

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.

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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.

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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What Is The Benefit Of New Propeller Blade Design

Blade shape has moved on in the last 15 years or so, thanks partly to computer aided design and a better understanding of what advantages a particular blade shape can offer.

The heavy sectioned blade is no longer the preserve of the plodding working boat, it can also be used to advantage on high-speed vessels where performance and economy are of equal importance.

Take a look at the original propeller on my own boat . Not much more than a three-bladed slab of bronze that did its job of pushing the boat through the water.

Three-bladed propeller: a workhorse that served Tony Davies boat well for many years

Now move on ten years and look at the sophisticated four-blade foil design that runs much more quietly, with less vibration and gives increased fuel economy at semi-displacement cruising speed.

A modern four-blade design that is more fuel efficient and more powerful

Pitch Prop Vs 19 Pitch Prop: Which Do You Need

Racing Boat 6717 Propeller 67mm Diameter For 6.35mm 1/4 ...

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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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.

Free To Use Propeller Sizing Calculators

Before you start, we would like to point out that these calculators are based on empirical data.They are not intended to perform complex cavitation or efficiency calculations.The results provide “best size” propeller dimensions based on your input data.There will always be a number of propeller size combinations that will work on your vessel, finding the best one is the trick.These calculators will help guide you to determine various combinations of power, gear ratio and propeller size for your vessel.Dueto the nature of these calculators, Victoria Propeller Ltd. will not accept anyliability, financial or otherwise, for the calculations or resultsprovided.

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To Grip The Water And Push The Boat

The result is the engine RPMs going above the specs and hitting the rev-limiter. Its exactly like what happens when the prop hub gets spun

On the opposite end of the spectrum, if were to install a prop with too big of diameter and pitch, then the engine wont have enough power to spin the propeller up to the right RPM range.

Causing the engine to never reach wide-open throttle and if ran like this for a long period of time, can eventually wear out internal components of the engine prematurely.

Its important to note that there are methods of getting propellers to turn up higher without changing the prop. This is usually done by venting the propeller some props have venting holes towards the bottom of the prop.

These holes can be either plugged or have the plugs taken out allowing water to flow freely through the prop without having to be pushed off the blades of the prop, causing force against it.

Find All Boat Propellers That Fit My Current Engine

Propeller Diameter & Pitch – a rough guide to choosing the right propeller for your boat

You will need to know your engine manufacturer, model and/or horsepower to determine which propellers will fit your boat. Once listed, you can then determine the size you are looking for. Once you provide the specifications on your engine, we will display all of the propellers that fit your engine. You will then be able to filter based on diameter, pitch, material, # of blades, etc.

Use our Propeller Guide to find the best and most cost effective 100% authentic and genuine propellers for your marine engine.

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Understanding Your Rc Boat Kits Propellers

Most RC boat kits come with more than one propeller, with many offering up at least three or four of varying sizes. This is by design, and each propeller is typically made for its own unique purpose.

Some propellers, typically the smaller ones, are made for slow-speed cruising. The larger the propellers get, the more likely it is that they are meant for racing, specialty waters, and stunt steering.

Its important to remember that the inclusion of a propeller in your RC boat kit doesnt mean that the prop is good to use for long periods of time at maximum power. Testing each propeller out can help you determine how conservative you need to be with your RC time.

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.

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