Q3 : What propeller should I use to improve hole shot and top speed?

A3 : Finding a propeller to improve your hole shot and top speed will be difficult. These are two separate characteristics that may take different propellers to achieve the goals. Generally speaking, a smaller blade high pitch propeller may have good top end performance, whereas a large blade low pitch propeller may have a good bottom end. For a light boat with plenty of power, a high pitch propeller with cavitation holes may work very well. However, a four stroke motor may not need a propeller with cavitation holes to achieve good acceleration and top end performance.

Q4 : How to install propeller accessories?

On the Propshaft A typical recreational boating propeller is mounted on a splined propshaft with a thrust washer, spacer, washer and nut, with some provision to keep the nut from turning loose, such as tabs on the washer or an additional cotter pin. There are exceptions, like the shear pin systems that were once widespread, but now most are as we describe here. Thrust Washer The thrust washer is mounted on the propshaft, between the lower unit and the propeller, and it may or may not have splines. It's an important component of a boat propeller's installation, because it fits the shaft in such a way that will not allow either itself or the propeller to move forward under thrust, thereby transferring thrust to the shaft and protecting the gear housing and its seal from contacting the rotating propeller. A matching taper on the propshaft and the washer is one effective design that stops a thrust washer from moving too far forward. The thrust washer also helps to keep the propeller centered on the shaft when the soft inner prop hub fails to do so under adverse high-torque conditions. Hub Inserted in the prop is a splined inner hub, which serves as a shock absorber between the prop blades and the shaft. A good prop hub should keep the propeller precision-centered on the propshaft, dampen vibrations and help protect the shaft from the severe shock of striking a submerged object with the propeller. There are two basic types of hub (in addition to some rare specialty hubs): a pressed rubber hub or an interchangeable hub. The pressed hub is semi-permanently forced into position by a high pressure press in a prop shop. By contrast, the interchangeable hub is easily inserted by the prop installer. Each propeller is designed to use one type or the other. While pressed hubs are made of rubber, interchangeable hubs are sometimes made of a more rigid material, but we find that rubber interchangeable hubs offer better vibration dampening. What's the difference between Rubex and Solas? Most Solas propellers are of the pressed rubber hub type and a few have specialty pin drive hubs. All Rubex props use interchangeable rubber hubs. There you have it! Spacer Like the thrust washer, the spacer assists alignment of the prop to the shaft when the inner hub is unable to hold its shape, only this time at the aft end of the prop. The spacer bears reverse thrust loads and prevents the inner hub from moving aft, with its large surface area. The final washer and nut prevent the spacer from moving aft. Many spacers are splined and some, for numerous Mercury, Mariner and Mercruiser applications, are also cogged or pinned to work in conjunction with an outer tab washer to prevent the nut from turning loose. Washer The washer helps fill space between the spacer and the nut, where the splines on the propshaft end and the threads begin. This helps prevent fore and aft play on the shaft by the prop. A tab washer can be used if the spacer is designed for one. Otherwise, a large traditional washer would be expected on an assembly that uses a cotter pin to retain the nut. When used, a tab washer's primary function is to prevent the nut from rotating in relation to the spacer. Prop Nut The prop nut secures the prop to the shaft and helps transfer reverse thrust to the shaft. Normally made of brass, a nylon locknut is used in conjunction with a tab washer or else a castellated (castle) nut is used with a cotter pin. Cotter Pin Where used, the cotter pin passes through a hole in the propshaft after the castle nut has been tightened with its slots aligned on both sides of the hole. Conclusion With so few pieces, a prop assembly is not complicated. Because each of the parts in the prop assembly performs an important function, it is important to use the correct parts and to install them all as intended. To maintain the correct positioning, spacing and integrity, each part must be made to match both the propeller and the drive unit that it's going on. Whenever doing a propeller installation, use your knowledge and pay particular attention to any instructions that may be provided with your prop or hub kit, especially concerning which parts to use.

Q5 : How to choose the right propeller?
　Recent advantages in outboard technology have made choosing the correct propeller for your boat both easier and more difficult--easier because the number of choices has doubled, and harder, for the same reason. Propeller manufacturers have been busy developing new 3-blade and 4-blade products and size ranges of stainless steel propellers to meet a growing number of hull types and horsepower ranges, especially for 4-stroke engines.
　　Four-stroke engines are designed to run at very specific RPMs, so pitch sizes have become available in 1 inch increments and new designs have appeared, each more tailored to a specific hull type and application. Propellers with higher rake angles and some with more surface area have been developed to maximize the power delivery of the 4-stroke torque curve.

Needs
　　The two most important things to remember in choosing a propeller are that it meet your individual needs for your individual application and that it allow the engine(s) to run within the specified RPM range at full throttle. Each boater and fisherman is trying to meet his requirements, but they can vary a lot.

　　What’s important to you and the way you fish: Top Speed, Cruising Speed, Hole Shot, Load Carrying, Slow-Speed Handling, Slow Trolling, Fast Trolling? Two identical boats with identical engines could be propped quite differently, depending on the usage, water conditions, and load. There is no such thing as the best or ideal prop for all applications of a similar nature. Acceleration may be compromised for top speed and fuel economy, and visa versa. Often times, there may be 6 or 8 different props that seem to run about the same, with differences so subtle that any of them could be considered satisfactory by most standards. This just makes it that much harder to make a decision and choose the right prop.

　　The purpose of this article is not to explain propeller theory or hydrodynamics, but rather to point out the various options in the market place and set some common rules of thumb. It will confine itself to the discussion of 3 and 4 blade stainless steels props as these are the most common in the real world.

Three Blades or Four?
　　In general, 3- blade props are the most common. They are available in wide size ranges and cost less than 4-blades. They typically yield a slightly higher top end speed than 4-blades. They are available in a wider variety of designs and offer more left hand rotation pitch options for twin counter-rotating engine applications.

　　Four-blades have some features of their own, though. They often provide more lift at the stern which will help accelerate the hull, especially if it is stern heavy. They come out of the hole strong and work well for pulling skiers and water toys. In fishing and offshore boats, they are oftentimes slightly faster than 3-blades at mid-range rpm’s, where coastal anglers most often run their engines. They also deliver slightly better fuel economy at mid-range rpm. Oftentimes, a poor-handling boat will improve by switching to a 4-blade propeller, and more often than not, a 4-blade will run smoother with better balance than the 3-blade equivalent.

　　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, you’ll usually need to decrease the pitch by 1 or 2 inches to keep the engine RPM in the same range.

Propeller Size
　　Propellers are sized and described by their diameter and pitch. A propeller listed as a 15 ? x 17 x 3 would indicate a 17 inch pitch, 3 blade propeller having a diameter of 15 ? inches. Pitch is the theoretical distance that the boat will move forward with each revolution of the prop shaft, minus the slippage. The pitch ultimately is responsible for the top speed of the boat, much like the main jet in a carburetor is responsible for the ultimate power and speed of an engine.

　The pitch must be matched to the engine’s recommended rpm range for full throttle. For most engines, this top range is about 500 to1000 rpm (typically 5,000-5,500 for 2-strokes, 5,000-6,000 for 4-strokes). A light boat and load will pull a high numerical pitch prop, whereas a heavy boat and load would have to run a smaller numerical pitch to load the engine less and allow the engine to reach recommended full throttle rpm. Keep in mind that most propeller manufacturers design their pitch in a progressive manner, to the point that the actual pitch will vary across the blade surface. Also, keep in mind that different propeller manufacturers each measure their pitch in slightly different ways with different tolerances. This means that two propellers of the same diameter and pitch from two different companies can yield different performance data.

　　For anglers slow-trolling for species like rockfish and flounder, a propeller with lower pitch (less distance per turn) that still allows the engine to rev to the top of its range will offer lower trolling speeds. It will also push loads easier and make maneuvering around a dock easier. On the other hand, a prop with more pitch that lets the engine turn to the lower end of its range may yield higher top speed.

Hooking-Up with the Water
　　There are other dynamics that come into play as the boat accelerates to its top speed. When it’s sitting still in the water and the skipper advances the throttle(s), the diameter and surface area of the prop develop the initial static thrust and launch the boat. As the hull gains momentum and speed, the dynamic thrust now is largely influenced by the prop’s ability to connect itself to the water and hook-up without cavitating or ventilating.

　　Cavitation is loss of hook-up due to the water literally boiling, caused by extreme low pressure near or at the blade surface or blade edge. Ventilation is a loss of hook-up due to the introduction of air or exhaust gases around the propeller. Basic blade design and diameter can affect these problems. If the diameter is too small for instance, it can cause cavitation. If the engine is mounted too high, it can cause ventilation. Both of these phenomena can be minimized by installing the correct prop. Going to a larger diameter or switching to a 4-blade can sometimes accomplish better hook-up. Larger diameter propellers usually yield better maneuverability as they push a larger volume of water on initial rotation, especially at slow speed. They also grab more water for better control when reversing. Matching the diameter and pitch for a given load and application gives the best performance for a specific boat.

　　Another design concept, called cupping, can also come into play here. Cupping means curling the trailing edge of the blade slightly to better grab water as it comes off of the blade face. This facilitates hook-up, but it can also load the engine more, much as adding pitch does. Different series of props have different amounts of cup in them. It is not uncommon today to have props with cupping added to the tip area of the blade to minimize tip losses and maximize efficiency.

　　Vented props are available with an exhaust relief hole at the base of each blade. These holes can range from ? inch to approximately 3/8 inches in diameter. They allow exhaust gases to escape around the propeller as it begins to spin up on acceleration. The engine gains rpm more quickly and reaches its ideal power curve sooner to improve overall acceleration. These props, however, do not work well for fishermen who do a lot of slow trolling, as the boat never gains enough speed to leave the ventilated water, causing the prop to catch-and-release, making the boat surge. Vented props also do not work well with cat hulls.

　　Matching style, blade design, pitch, and diameter is just as important for boat handling and safety as for maximizing cruising speed and fuel efficiencies. Large diameter props with lots of surface area help a boat climb a big wave and allow the operator to maintain good control in offshore conditions with rough water. Again, good-hook up is essential without overloading the engine and prop to the point of causing cavitation.

Conclusion
　　If you can find a prop that seems to feel good and run with confidence, don’t be discouraged if it’s off by a little bit in ideal engine rpm. Any competent prop shop can fine-tune and tweak a good prop to make it perfect for your application. Adding or removing pitch up to 1 inch is not uncommon. Adding or removing cupping is also a standard adjustment. It is nearly impossible to find the right prop without going through a dedicated session of trial and error. With so many styles, designs and options in the market today, there is much to be gained by simply trying as many props as you can. It is important to do any comparative analysis between props in the exact same water conditions as each other, so that you can actually come away with usable data.

　　Each of us has unique desires and requirements for our propeller choices. They should always be matched to a particular hull, load and usage. My personal desire is to find a prop that I consider to be well balanced. By that, I mean one that handles well, yields average mid-range and top speeds, with no quirkiness or negative traits. I am always willing to sacrifice top speed to achieve good all-round performance, as I run wide open no more than 10% of the time, due to water conditions, comfort level and passenger security.