- Written by Daniel Robertson
Selecting the right propeller for your boat and engine combination: The proper propeller size for your boat and engine combination is based on the wide open throttle operating range for your particular engine. This can be located in your operator's manual. This will be expressed in terms of a certain horsepower at a certain RPM.
The goal in propeller selection is to determine what propeller style and size will maximize performance for your boat, while allowing your engine to operate in the recommended RPM range. The correct propeller will prevent the engine from over-revving, yet allow it reach the minimum RPM where maximum horsepower is produced.
Using your existing propeller, determine what is the maximum RPM you are able to obtain. If during this test, you begin to exceed the maximum rated RPM of the engine, reduce throttle setting to a position where maximum RPM is not exceeded.
If your test results in your being able to over-rev the engine, you need to increase the pitch of the propeller. Increasing the pitch increment by 2" will result in approximately a 300-400 RPM drop. If your testing shows, however, that you are only able to obtain an RPM somewhat lower than the maximum rating given by your engine manufacturer, you would need to decrease pitch. Decreasing pitch would increase your RPM.
Switching form an uncupped to a cupped propeller will also reduce your RPM. The cupped propeller of the same pitch and diameter will typically reduce your RPM by approximately 200.
Once your wide open throttle RPM falls within the recommended range of the engine manufacturer, you have a propeller that is suited correctly for your boat with respect to RPM. You may, however, not be satisfied with respect to skiing performance or trolling speed. It is best in circumstances like this to have two propellers. One to accommodate on set of circumstances and the other to perform best under the different load. It could, in fact, be that more that one propeller will be suitable for your boat and motor combination depending on your usage. It is imperative, however, that the wide open throttle RPM fall within the range specified by your engine manufacturer.
- Written by John Smith
The propeller that came with your new engine isn't necessarily the one that is best suited to your needs. This is because many original equipment props, understandably, are made to meet a range of average conditions for many kinds of boats, hull styles, and loads. This can limit their performance. What you need is a propeller specifically selected for your kind of boat, and your style of boating.
The size of a propeller is described using two sets of numbers. These correspond to the diameter and pitch. The pitch always follows the diameter when describing a propeller.
Diameter: Diameter is two times the distance from the center of the hub to the tip of the blade. It also can be looked at as the distance across the circle that the propeller would make when rotating. It is the first number listed when describing a propeller.
- Written by Jim Fachs
Fuel vapor pressure is a measure of how easily fuel sample evaporates. Any additives used in gasoline contain aromatics. Aromatics are light hydrocarbons distilled off the top of a crude oil sample. They are effective at increasing the research octane of a fuel sample but can cause vapor lock (bubbles in the fuel line) on a very hot day If you have an inconsistent running engine an you suspect a vapor lock, use a piece of clear fuel line to look for bubbles, indicating that the fuel is vaporizing. One negative side effect of aromatics is that they create additional combustion products such as carbon and varnish. If your engine requires high- octane fuel, to prevent detonation, de-carbon the engine more frequently with an internal engine cleaner to prevent ring sticking due to excessive varnish buildup.
- Written by Roberto Bell
It is important that you choose the right engine or prop for your boat if you want it to operate at the manufacturer's maximum recommended engine RPM and if you want something suitable to the type of boating you do. If you have an engine that doesn’t reach the recommended RPM when at full throttle then you will be getting an over propped condition which leads to lugging.
Placing this much strain on the engine can lead to damage. If an engine goes beyond the recommended RPM then it will experience higher than normal wear. This is why selecting the right propeller is important in the performance of your boat. The following tips will help you to choose the right prop for your boat.
When it comes to boat propellers they are often described by the diameter and pitch. If you have a smaller engine or boat you will generally want a smaller diameter prop. If you have a lower pitch on your prop then you will have greater acceleration and pulling power. A higher pitch prop will make your boat go faster but only if the engine has enough power to keep the RPMs at their optimum range. So make sure you select a prop size or diameter and pitch that works within the correct RPM range for your engine.
Next you need to consider the number of blades on the prop. Just a slight change in the number of blades may require a minimal adjustment in the diameter and pitch to keep the RPMs within their proper range. Generally you can use a three to four blade prop without having to worry about much of a change in performance.
The biggest difference between the three and four blade propeller is the handling. Three blade propellers are preferred for general or all-purpose use since they give good acceleration and control with excellent top speed performance. On the other hand, the four-blade option is best for those who want great acceleration, more bow lift and excellent pinpoint steering.
Now you should consider the material used in constructing the propeller. Propellers are typically made out of composite, aluminum or stainless steel. Composite propellers are preferred for good performance, durability and a low price. Aluminum propellers are the most common and have the widest range of applications. Stainless steel is the most expensive but give you the best in performance and durability.
Finally you should consider cupped propellers. These have special curved trailing edges that help the propeller to maintain their performance at a higher level if you want to take the corners tighter. If you want to achieve a higher top-end speed performance. These types of propellers also help to provide more efficient fuel consumption.
The main goal of choosing a proper boat propeller is to select one that allows the engine to achieve its optimal wide-open throttle. This is typically between 5000 and 5500 RPM for outboard motors and 4400 to 4800 for stern drives or depending on the type of engine you have. You can find the specific information through the owner’s manual of your boat or engine.
- Written by Jim Fachs
A fuel’s octane rating is a measurement of how stable the fuel is when heat is introduced. Octane rating is a major consideration when deciding whether a fuel is suitable for a particular application. For example, in an engine, we want the fuel to ignite when the spar plug fires and not before, even under high pressure and temperatures.
Once the fuel is ignited, it must burn slowly and smoothly, even though heat and pressure are building up while the burns occurs. The unburned fuel should be ignited by the traveling flame front, not by some other source of ignition, such as carbon deposits or the heat from the expanding gasses. A fuel’s octane rating is known as a measurement of the fuel’s anti-knock properties.
A fuel higher octane rating can be subjected to a more severe combustion environment before spontaneous or abnormal combustion occurs. To understand how two gasoline samples can be different, even though they have the same octane rating, we need to know how octane rating is determined.
A universal method of determining the octane rating of a fuel sample was developed. The rating you see on the pump at a fuel dock is known as the pump octane number. The small print on the pump has a rating formula. The rating is determined by the R+M/2 method. This number is the average of the research octane reading and the motor octane rating.
The Research Octane Rating is a measure of a fuel’s anti-knock properties under a light load or part throttle conditions. During this test, combustion heat easily dissipated.
The Motor Octane Rating is a measure of a fuel's anti-knock properties under a heavy load or full throttle condition, when heat buildup is at maximum.
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