Help Boat Prop Has Play In It Troubleshooting Tips
I was talking to my neighbor over the weekend, and he was asking me if I knew if a prop should have a little movement when its tighten. I wasnt sure, so we took a look at my outboard engine that I have sitting in my garage, and mine didnt have any movement.
A properly tightened prop should not move back and forth or show any signs of play in it. If it does, you should remove the prop and determine what the issue is that is causing it to move around.
After trying to find my neighbor some answers online, I was able to piece together some really helpful information that Ill share with you below.
How To Fix A Slipping Prop
Sometimes the problem is bigger then what you can do on your own. You might have to take the propeller to a boat repair shop and have them press the bad hub out of the propeller, and then press a new one in its place. Shops usually charge around $40 for this type of repair.
If the shop can not press a new hub in the propeller, you might have to look at buying a whole new propeller instead.
But often, fixing a slipping prop could be something that you can do yourself. There are a few things that you can try doing to fix the problem.
#1. Check the Keyway:
- Remove the propeller from the shaft.
- Remove the key.
- Set the prop back on the shaft .
- Take a file or lipstick and make a mark a line on the shaft of the bow side of the prop.
- Remove the prop and insert the key back into place.
- Slide the prop back over the shaft and set it into place so that the lines match up.
- If it doesnt match up, remove the prop and key.
- Using a file or sandpaper, take the key and grind a little bit of it down. . Reset the key in its proper place, and then slide the prop back on. Repeat this step until the prop is back to lining up correctly with the mark you made.
- Tighten the prop nut, and hopefully, this fixes the problem.
#2. Cracked Hub:
- Remove the propeller and examine the prop hub.
- If you notice a crack, replace just that part.
- Set the new prop hub in place, slide the prop on, and tighten the prop nut.
#3. Loose Nut:
#4. Shear Pin:
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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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.
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.
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The Parts Of A Boat Propeller
Everything you ever wanted to know about your boat’s propeller.
Your propeller affects every aspect of your boats performance: acceleration, handling, ride, turning, fuel efficiency and top speed. The trick is finding the right prop for your boat, and the right prop for how you use your boat.
It would be easy if props were simple, but boat propellers are science and engineering, tribal knowledge, feel, art and, yes a little magic. Like the ocean, the subject is broad and deep, and those attempting to navigate it often find the endeavor is fraught with rough spots. As such, many boaters find it hard to solidify propeller knowledge.
On the theory that smaller chunks are easier to swallow, were going to zoom in and focus primarily on a smaller piece of the propeller pie. Join us as we define and explain the parts of the propeller. This should prove a neat refresher for old salts, while others will be provided the basis for intelligent conversation with boat dealers, prop vendors and fellow boating enthusiasts.
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Starcraftsummerfun Webisode : How To Choose A Propeller For Your Boat
How to choose a propeller for your boat can be a tricky topic. Many people can point out their propeller on their boat, but that’s usually about it. When you start asking about pitch, diameter and 3-blade vs. 4-blade they look at you like you’re speaking Mandarin. Well the fact of the matter is, is that the person who is going to know the most about your propeller is your local dealer. But this does not mean you should’t at least have a working knowledge of propellers so you can talk the talk and figure out if you’re running the right pitch.
Pitch is a great place to start as it is the most common measurement when dealing with prop choices, as well it has the most direct relation to performance. The pitch refers to the distance a propeller travels in one full roation.
The Propeller’s pitch is going to effect your engine’s RPM by either increasing it or decreasing it. The rule of thumb for this is if you go UP in Pitch you go DOWN in RPM and vice versa.
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To Pitch Up Or Pitch Down
This is an integral question that must be answered before you buy the new propeller. As explained, by increasing your prop pitch, you will be effectively decreasing the engines rpm and vice versa.
Since the general rule of thumb is that every two-inch increase in pitch decreases the engines rpm by about 400 revolutions, if you find that your boat is under revving, then you might want to consider getting a propeller with a lower pitch and vice versa. If your boats issue is that its over-revving, then getting the 21 pitch propeller might be the best solution.
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The beauty of all this is that your boat manual will have the desired specifications, but you could also ask your mechanic or even your dealer to advise which prop pitch would be the perfect solution for your specific boat. Just remember, one of the most important considerations here is your performance goal. What is it you want the boat to do exactly?
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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Bad Propeller Symptoms To Look For
Propellers are designed in such a way that if your propeller is bad or damaged, this will have an impact on your fuel efficiency, as well as performance. A damaged propeller will slow your boat down, affect how long an engine will last, as well how smooth the ride is on the open water.
Here are some symptoms to look for in your propeller:
Visually:Can you see any chips, nicks, dents, missing a blade, or any other sign of damage to the propeller? If so, it might be time to replace that propeller with a new one. A lot of marinas and repair shops will not attempt repairing a damaged propeller because of the sophisticated design they have.
Tangled: Often you might find that your propeller has some fishing string or seaweed wrapped around the propeller and shaft. If this happens, you need to remove the propeller and untangle the object wrapped about the shaft and propeller.
Movement:If you can grab hold of your propeller and move it back and forth, or wiggle it around a little bit, then you do have a problem that would require your immediate attention.
A few things could cause this.
- Worn key
- Crack in the hub
- Loose prop nut
Crack in hub: Remove the prop and examine the hub of the prop for visible cracks. Cracks might be hard to see, so even if you do have a crack in the hub, you might not also be able to see it. Even a small hairline crack in the hub could cause the prop not to fit tightly. This problem is not as common, but it is something to keep an eye out for.
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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.
How To Use The Boat Prop Calculator Tool
Knowing the theoretical speed for your boat can help you select the proper pitch. To use our boat prop calculator, you need four inputs:
- RPMs: Revolutions Per Minute. Enter the high end of the operating range established by the engine manufacturer or the maximum RPMs you can attain with your current propeller. The recommended operating range should be listed in your owners manual and can also be found online.
- Pitch: This is the theoretical distance the propeller would travel through the water with each revolution . Think of a screw going through wood. It is often stamped on the outside of the propeller. In this example, the propeller has a 24 pitch.
- Gear Ratio: This is the number of drive shaft revolutions for one revolution of the propeller. You can find this in your owners manual or by searching online.
- Prop Slip: This is the relationship between the actual vs. theoretical distance your boat travels with each revolution of the propeller and is impacted by the hull design, weight of your boat, propeller design and other factors. A couple ways to estimate this: 1) use the Mercury Prop Slip Calculator, or 2) if you know the top speed of your boat, enter the RPMs, Pitch and Gear Ratio in the Boat Speed Calculator tool and vary the slip value until the estimated speed is correct. For example, I have a boat with a max RPM of 5,800, my propeller pitch is 24 and the gear ratio is 1.92. Based on these inputs, a Prop Slip of 13% get me to my correct maximum top speed of 60 mph.
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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.
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.
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How To Choose The Right Prop For Your Boat
The proper propeller size for your boat and engine combination is based in part on the wide open throttle operating range for your particular engine. You can find this in your operator’s manual, expressed in terms of a certain horsepower at a certain r.p.m.
The goal in propeller selection is to determine what style and size will maximize your boat’s performance, while allowing your engine to operate in the recommended r.p.m. range. The correct propeller will prevent the engine from over-revving, yet allow it to reach the minimum r.p.m. where the maximum horsepower is produced, with ideal engine loading.
Using your existing propeller, determine your maximum obtainable r.p.m.. If during this test, you begin to exceed the maximum rated r.p.m. of the engine, reduce the throttle setting. If the engine over-revs beyond the maximum recommended r.p.m., you may need to increase the pitch of the propeller. Increasing the pitch increment by 2″ will result in approximately a 200-400 r.p.m. drop. Also, switching from an uncupped to a cupped propeller will reduce your r.p.m . The cupped propeller of the same pitch and diameter will typically reduce your r.p.m. by approximately 200. If you cannot reach maximum r.p.m., then pitch should be decreased. These recommendations apply to single engine installations only. For most twin engine installations it is necessary to increase pitch by 4″.
Are More Blades On A Prop Better
Contrary to popular belief, many boaters think that propping their boat with a prop containing more blades equates to better performance. To an extent, this is true. However, we have to consider several other variables such as the physics of the boat, propeller, and the water.
The more a boat is submerged in the water, the more drag is created. In turn, the more contact we have with the water, the better overall control we have of the boat. Nevertheless, more water contact also means slower boat speeds.
This concept also applies to the number of blades that the prop contains the more blades a prop has, the more drag it creates, in turn giving us a lower top-end wide throttle speed.
Running the correct prop, in the long run, is going to save you some money because it improves your mid-range cruising performance. If you are running a small prop, you will burn more fuel running higher RPMs in order to stay on plane at a decent speed.
Running too big of a prop, on the other hand, means that you will never hit wide-open throttle and this will eventually lead to carbon build up along with poor performance.
With the correct prop, we can cruise at the optimal mid-range RPM while simultaneously burning the least amount of fuel possible. A win-win for both your fun, wallet, and boat!
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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!