Boat Maintenance & Repairs ·Aug 16, 2026

The Correct Prop For Your Boat! How to Know! [VIDEO]

Video Transcription

It's Technicians Tuesday everybody and the hope is that everyone had a Merry Christmas and a happy new year tonight. This week the focus is on learning all about propping out a boat, why it's important, how to do it, and what finding the correct prop for your boat means for your wallet. This week's contest prize is some boat cleaning supplies from Better Boat so smash that subscribe button, get the bell on and let's talk about some props.

They are the wheel of the boat and they come in all kinds of different styles and sizes from two blades to six blades from little props to big props. It's important to understand how they work because they affect the performance and the fuel economy of your boat. A propeller is measured in diameter and in pitch. The diameter is how big around the prop is and the pitch of the blade is defined as the theoretical distance the prop will move through the water in one revolution or turn. So a 19 pitch prop is theoretically going to move 19 inches through the water in only one turn. Now think about that at 6,000 RPMs, that's slicing through the water.

The keyword here though is the theoretical distance. If it wasn't theoretical then it would be said that the bigger the pitch the better the prop but that's not really the case. The physics of the boat, propeller and the water must be considered. The more of the boat that is in the water the more drag. Yes the more contact that the boat has with the water the better control there is but it also slows things down. The same goes for the prop. The bigger the prop, the more drag there is. This goes for the number of blades that the prop has as well. The more blades that the prop has the more drag it will have and the less top end wide open throttle speed there will be.

It's important to note that the discussion here is about the average recreational boating and fishing application. Racing is not the focus here, though the physics don't change; there are way more variables to consider for racing than what is covered here today. Going from a three blade to a four blade without changing the diameter or the pitch of the prop will mean losing top end speed. What gets gained though is the whole shot. The time it takes to get the boat out of the water will be way quicker because of that extra blade which gives more grip from the prop to the water. With that extra grip there is also better control and handling. Understanding these things are the base foundation for beginning the propping procedure to get the right prop for your boat.

Now each engine is going to have a top end wide open throttle RPM range. Each engine that has been manufactured in the last 20 years is also going to have what is called a rev limiter. The rev limiter is going to stop the engine from going over a certain amount of RPMs. A Verado makes a good first example. The RPM range for most Verados is 5,800 to 6,400 RPMs and the rev limiter is set to 6,500. On a 300 horsepower Yamaha the RPM range is 5,000 to 6,000 RPMs and the rev limiter is set to 6,300. The rev limiter setting isn't as important to know; it's the RPM range of your engine that you need to know about.

If a small diameter prop is put on an engine with a low pitch the chances are that the power of the engine is going to power through the ability of the propeller to grip the water and push the boat. This results in the engine RPMs going above the specs and hitting the rev limiter. It's exactly like what happens when the prop hub gets spun. For all of you that have experienced spinning a hub before you can remember what that's like. On the opposite end of the spectrum though if a prop with too big of a diameter and pitch is used then the engine won't have enough power to spin the propeller up to the right RPM range causing the engine to never get to wide open throttle and if ran like this for a long period of time can eventually wear out internal components of the engine prematurely.

There are ways to get propellers to turn up higher though without changing the prop. This is done by venting the propeller. Some propellers have venting holes already on them towards the bottom of the prop. These holes can either be plugged or have the plugs taken out of them. What this does is allows water to flow through the prop without having to be pushed off of the blades of the propeller creating force against the prop. This is useful in a wide range of applications but the topic of how to properly choose the correct prop for the boat still needs to be addressed.

Knowing about the RPM ranges, the pitches and the diameters of the prop as well as the ability to vent a prop and go from three to four blades or vice versa is important, but actually propping out the boat is a process of trial plain and simple. An educated guess of a prop to start with is needed, then take the boat out and try it and go from there. Before doing anything though the conditions of the boat make a huge difference. Things like the amount of fuel in the tank, how many people are on board and what kind of gear is being carried as well. A boat can be propped out with an eighth of a tank of gas with just one person on board.

The RPM may come out correctly but when it comes time to use the boat normally it will definitely be different. That is because for adults weighing 200 pounds a piece, a hundred gallons of fuel weighing 600 pounds, two coolers full of ice, food, drinks and bait weighing about 150 pounds, eight rods and reels, the live well full of bait and water being roughly 250 pounds now the boat weighs almost 2000 pounds more and this could be a conservative number depending on the situation. That prop that was spinning let's say 5,800 is now only turning up 55, 54 or maybe only 5,200 RPMs which means that the boat is no longer propped out correctly. The more weight that the engine and the propeller has to push is ultimately what decides what prop to use.

A prop can be chosen based on the recommended propeller from the factory or manufacturer of the boat. The previous prop that was running in a repower situation can also be used just for trying. Install the prop and take the boat out for a test drive to try it. Let's say there is a 15 inch diameter prop with a 15 pitch.

The engine RPM range is 5,000 to 6,000 RPMs and there's close to the right amount of weight onboard that will normally be there. At wide open throttle the engine turns 6,300 RPMs and is hitting the rev limiter. This means that the prop is too small and isn't big enough to push the weight of the boat so that prop can be swapped out for one with say a 15 and a half inch diameter and a pitch of 23. So after taking the boat back out this time only 5,400 RPMs are reached. Now the prop is too big. Given these numbers the same diameter can be kept and the pitch dropped back down to 21, which should yield roughly 58 to 5,900 RPMs, meaning the right prop has been found.

Trimming up during this process needs to be addressed though. Normally the boat won't be fully loaded when propping it out. It's best to prop it out towards the top end of the RPM range without trimming the engine. The goal is to be able to add some trim to the engine and come really close to hitting the rev limiter under these conditions. That is because whenever the boat is loaded up and taken out under normal conditions, there will still be some room to add some trim at wide open throttle and have the RPMs come all the way up to the top end of the RPM range. If the engine has to be trimmed up to get to the top of the range then after the boat is loaded the top of the range won't be reachable because of the weight that has been added to the boat.

Now that you know how to prop out your boat let us know about your experience in the comments below. Make sure to include a hashtag clean boat for the contest prize, follow Better Boat on Instagram and let's talk about what having the right prop means for your wallet. Running the correct prop is going to save some money because it improves mid range cruising performance. If running a small prop more fuel will be burned running higher RPMs just to stay on plane at a good speed. Running too big of a prop means that wide open throttle will never be hit and that will lead to carbon buildup along with poor performance. With the right prop though cruising at an optimal mid range RPM with a little trim burns the least amount of fuel as possible.

As far as the three blade versus four blade debate that is ultimately up to you and what you are looking to get from your boat. Would you rather have a better whole shot or top end speed? The decision is up to you. Running larger boats close to the 30 foot or higher range generally running the four blade is best because of the size and weight of the boat. That extra blade really makes a difference in getting the boat up out of the water and controlling it at higher speeds. Don't forget to hit that like button and introduce Better Boat to your boating community by sharing with a boater you know. Thank you for hanging out today. See you next week. Here's hoping everybody has a happy new year.