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Mercury Mercruiser Propellers

Traditionally, propeller selection has been approached with apprehension, a "black art" of sorts. We've tried to take away some of the mystery surrounding propellers and replace it with facts you can use. By reading this information and referring to the application guide*, you too, will be able to make intelligent propeller choices.

Best all-around performance is achieved when wide open throttle (WOT) engine operation occurs near the top of (but within) the wide-open-throttle RPM operating range designated by the manufacturer for that specific engine. Selecting the wrong propeller not only reduces performance, but, in fact, can damage the engine.

An engine that does not reach the recommended RPM at wide-open-throttle is in an "over-propped" condition, resulting in "lugging." This high-torque operation puts a tremendous load on the pistons, crankshaft, and bearings. This may cause engine damage.

On the other hand, an engine that revs past the recommended RPM will have higher than normal wear and can also be damaged by fatigued parts breaking and passing through the engine.

That's why it's essential that your engine is propped correctly for your boat/engine combination and the type of boating you want to do. To make this selection, propeller charts are published as guidelines for general applications of Mercury Propellers. They are not intended, however, to be an absolute recommendation, as boats and operating conditions vary. Use the guidelines suggested here, but remember, the best propeller for your boating needs can be determined only by experimentation.

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How to read a propeller selection chart

Mercury Propeller charts include a boat speed range that is directly related to gross weight and boat length. The interrelation of these factors has a marked effect on the speed and performance of boats that fall within any given category. Generally, gross weight is the major factor (total weight of the entire package -- boat, motor, fuel, passengers, and miscellaneous equipment). When choosing a propeller, this should be the primary consideration.

Propeller lines normally are designed so that each inch of pitch will change engine RPM by 150 to 200. So, if the engine RPM falls too low on your first propeller selection, try a lower pitched propeller to bring the RPM up. Higher-pitched propellers reduce the engine RPM.

Pitch Change Calculation

There's an easy calculation to determine how much pitch change may be required. Just follow these steps:

1.Check the specifications in your operator's manual for the recommended operating range at wide open throttle (WOT) for your engine. A tachometer is necessary to determine the WOT RPM.

2.Run the boat/motor combination at WOT to determine the maximum RPM. Adjust engine trim angle for optimum performance.

3.If the WOT RPM is below the recommended RPM range of the engine, note the reading of the tachometer. Take that reading and subtract it from the top end of the operating range.

Example: Operating range = 5000-5600 RPM
Top End of operating range = 5600 RPM
Tachometer reading = 4800 RPM
Difference = 800 RPM

4.For every 1 inch of pitch change, the effect will be approximately 200 RPM. Knowing this, take the difference in the above example at 800 and divide it by 200. The result is 4. The next propeller to try will be 4 in. in pitch less than the propeller that was first used. You should now either have the right propeller or be only one size off.

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Single- and Multiple-Engine Application

In single-engine installations, right-hand rotation propellers are almost always used. This is merely the result of tradition, but is perpetuated by nearly all recreational boat manufacturers placing their operator's position on the right-hand side to compensate for the boat roll resulting from a right-hand rotation propeller.

When a boat is equipped with dual engines, counter-rotating propellers are preferred. This balances any steering pull when the outboards or drives are trimmed evenly. Most boat manufacturers prefer to rotate the propellers "out." That is, right-hand rotation on the right side, left-hand rotation on the left side, believing that overall handling is slightly better. This can also afford more balanced steering when forced to operate with only one engine. Many older twin engine boats use propellers of the same rotation. The disadvantages are that steering torque is greater when trimmed well in or well out (assuming no power steering) and, in very rough water, if a hull goes airborne, a pair of right-hand propellers (for example) can walk the stern to the right a little.

High-Performance Applications

The Revolution 4, Mirage Plus, Tempest Plus, Bravo One Performance, and the Offshore series of propellers are available for the high performance enthusiast. The Mirage Plus and the Bravo One Performance propellers are designed for big-block V-8 Bravo One sterndrive applications. The larger diameter and blade area, when coupled with a higher horsepower engine, produce excellent acceleration, holding and superior top-end performance.

For twin V-6 outboard-powered boats, use a Mirage Plus 3-blade, or a 4-blade propeller such as the Alpha One Performance or Offshore series propellers. They offer outstanding lift for carrying heavy loads. Many twin V-6 boaters report better mid-range cruising speeds, reduced steering torque, and rough water handling when using 4-blade propellers.

The Tempest Plus, the small tube Trophy Plus (4.25 in. tube), and the Laser II offer great planing abilities and top speed for many other V-6 outboard packages.

Some lighter tunnel bottom shaped hulls require very high pitched (above 25 in.) propellers. This type of hull generates bow lift aerodynamically and does not require the propeller to assist in this function. Cleaver propellers, which provide very little bow lift, are most effective on this type of boat.

Propeller applications for outboard and sterndrive-powered boats that have speed capabilities above 90 MPH fall into the very high-performance or racing categories and go beyond the scope of consumer-oriented high-performance pleasure boating. If you have question about props for this speed range, contact Mercury Hi-Performance at 920-924-2037.

Mercury Propellers have long been the best performing props in the water. We've made a firm commitment to stay ahead of the competition by incorporating innovative designs and using only the finest materials. State-of-the-art tooling and highly skilled craftsmen are two more reasons why, when you own a Mercury propeller, you have the highest quality propeller available. Find out how a Mercury prop can make your current boat even better. The Mercury line of propellers: because the difference is performance.

Black Max Series

Quality die-cast 3-blade aluminum
Eye-catching high gloss Phantom
Black finish
Easy to maintain & repair
6 in. - 25 in. pitch

Alpha 4


4-blade die-cast aluminum propeller
Better acceleration and handling than
3-blade
Right-hand and left-hand rotation
16 in. - 20 in. pitch

Vengeance

Better acceleration & handling than
3-blade aluminum propeller
Proven 3-blade design
Patented Duratec gloss finish
Right-hand rotation, left-hand
rotation available in some pitches
9 in. - 25 in. pitch

Laser II

Lots of lift for lightweight hulls
Thinner blades to reduce drag
Right-hand and left-hand rotation
19 in. - 26 in. pitch

Revolution 4

Wakes up single engine sport boats
Dramatically improves mid-range
Strong accelleration and top speed
19 in. - 23 in. pitch

High Five

Patented 5-blade stainless technology
Smooth-as-silk acceleration
Pulls skiers effortlessly
17 in. - 26 in. pitch

Trophy Plus

Patented 4-blade stainless steel design
Quicker hole shot, improved
mid-range speed & amazing handling
Reduced steering loads
17 in. - 26 in. pitch

Tempest

Large diameter for high transom heights
3-blade stainless design creates greatbow lift
Excellent for heavy sport & bass boats
21 in. - 27 in. pitch

Offshore Series

Tremendous lift for big, twin engine boats
4-blade stainless steel features glossy Duratec finish
Left Hand & Right Hand rotation
17 in. - 23 in. pitch

Mirage Plus

Dramatically improved to handle high horsepower applications
Improves acceleration & top speed on many boats
Left Hand & Right Hand rotation
13 in. - 29 in. pitch

Bravo One

Outstanding 4-blade stainless propeller for high-performance
Great mid-range speed and top-end handling
Solid hub available
Right-hand and left-hand rotation
22 in. - 30 in. pitch

Bravo II

Created to enhance the Bravo Two drive system
Large blade area to increase efficiency
Aluminum or stainless, 3 or 4 blade
11 in. - 25 in. pitch

Bravo Three

Twin counter-rotating propellers
Durable stainless steel
High-thrust blade geometry
20 in. - 30 in. pitch

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Switching Among Propeller Types/Families

When changing from 3- to 4-blade, are the pitches the same?

If you're changing to propellers manufactured by Mercury, the answer is "yes!" For example, a 4-blade propeller is designed to run at elevated transom heights (normally 2 to 3 inches above the transom). The 4-blade's aggressive blade design and larger diameter help gain a performance advantage. When compared to a 3-blade propeller at the same transom height, the 4-blade will exhibit a lower engine RPM but, when the engine is raised to the proper operating height, the RPMs of both propellers are close.

When upgrading from an aluminum propeller to stainless steel . . .

The most important concern to be aware of is the correct RPM range for your engine. The propeller pitch regulates the engine RPM. Each inch of pitch is worth about 200 RPM. Lowering the propeller pitch (going from a 23 pitch to a 21 pitch) will increase the engine RPM (about 400 RPM). Increasing the pitch (23 pitch to a 25 pitch) will decrease engine RPM. Most applications will match up pitch to pitch and this is the best starting point.

In some instances, Mercury offers propellers in even pitches (20, 22, 24, etc.). In these situations, go to the next higher pitch (24 pitch stainless to replace a 23 pitch aluminum). If your aluminum was already operating at the top of the RPM range, the higher pitch propeller will allow you to see where you fall in the RPM range with the new propeller without over-revving.

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Bullock Marine offers new & used powerboats as well as performance boat accessories: skater, fountain, eliminator, Mercruiser Mercury Marine (competition - racers & performance propellers, Zero Effort Controls™, K-Plane™ high performance trim tabs, Mercury Racing Trim Indicators™, high performance engines, competition drive, etc.) cigarette boat, welcraft, scarab, donzi boats, catamaran raceboat, high speed twin hull, etc. Bullock Marine is an authorized dealer for Douglas Marine Skater Powerboat, Regy Fountain powerboat & sport boat, Eliminator powerboat & sport boat, and Mercury Mercruiser marine engines, Drive & accessories.

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