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Frequently Asked Questions

Tacoma Propeller offers you some commonly asked questions from our over 50 years of experience in the boat propeller, repair and parts business. If you need any further help or have more questions please feel free to call us at 253-272-5065.

 

HOW DO YOU READ THE PROPELLER DIMENSIONS?

14-1/2 X 19 RH 3 Blade SS Apollo Propeller
14-1/2 : The propeller diameter. The diameter is always the first set of numbers.
19 : The pitch of the propeller. The pitch is always the second set of numbers.
RH : This is the propellers rotation. Either RH clockwise or LH counter clockwise.
3 Blade : This is the number of blades. It can be 2, 3, 4, or 5 blades.
SS : This represents the propeller material. AL = Aluminum & SS = Stainless Steel.
Apollo Propeller : This is the style or brand of the propeller.


HOW IS PROPELLER DIAMETER MEASURED?

The diameter of a propeller 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. The propellers diameter is the first number stamped or embossed on the propeller and the first number when describing a propellers dimensions.

 


HOW IS PIECH OF A PROPELLER MEASURED?

Pitch is defined as the theoretical forward movement of the propeller during one revolution, assuming there is no “slippage” between the propeller blade and the water. For most boats, there is slippage and therefore the distance advanced is less than the design pitch. The amount of slippage varies from boat to boat. The propellers pitch is the second number stamped or embossed on the propeller and the second number when describing a propellers dimensions.

 


WHAT IS PROPELLER ROATATION?

From behind the boat looking forward to the propeller(s), a right hand propeller rotates clockwise and a left hand propeller rotates counter clockwise. Many single engine boats rotate clockwise using a right handed propeller. Two propellers rotating the same direction on twin screw boats will create steering torque. In other words, two right handed propellers pull the stern hard to the right and the bow to the left.

Two counter rotating (opposite direction) propellers on twin engine boats eliminate this steering torque because the left handed propeller balances out the right hand propeller. This results in better straight line tracking and helm control at high speed.


WHAT IS PROPELLER RAKE?

Propeller rake is the degree that the blades slant forward or backward in relation to the propeller hub. Rake can affect the flow of water through the propeller, and has implications with respect to the boats performance.

Aft rake helps trim the bow of the boat upwards, which often results in less wetted surface area and therefore higher top end speed. Aft rake propellers also typically bite better on ventilating type applications. Forward or negative rake, helps hold the bow of the boat down. This is more common in workboat type applications.


WHAT IS PROPELLER CUP?

Many of today’s propellers incorporate a cup at the trailing edge of the propeller blade. This curved lip on the propeller allows it to get a better bite on the water. This results in reduced ventilation, slipping, and allows for a better hole shot in many cases. A cupped propeller also works well where the motor can be trimmed so that the propeller is near the surface of the water. The cup will typically result in higher top speed on one of these applications.

 


WHAT IS CAVITATION?

Cavitation, which is often confused with ventilation, is a phenomenon of water vaporizing or boiling due to the extreme reduction of pressure on the back of the propeller blade. Many propellers partially cavitate during normal operation, but excessive cavitation can result in physical damage to the propeller’s blade surface due to the collapse of microscopic bubbles on the blade.

There may be numerous causes of cavitation such as incorrect matching of propeller style to the boats application, incorrect pitch, physical damage to the propeller, etc. Be advised disturbances in the water flow forward of the propeller can result in blade damage which appears to be cavitation, but is actually due to non-favorable water flow to the propeller.


WHAT IS VENTILATION?

Ventilation is a situation where surface air or exhaust gasses are drawn into the propeller blades. When this situation occurs, boat speed is lost and engine RPM increases rapidly. This can result from excessively tight cornering, a motor that is mounted very high on the transom, or by over trimming the outboard motor or sterndrive.

 

PROPELLER PERFORMANCE

WHY WON’T MY STERNDRIVE PERFORM AS WELL AS OTHER DRIVE OF COMPARABLE BOAT LENGTH, BEAM, AND WEIGHT?

Differences in hull design, such as dead rise, position of water gravity and transom angles can account for significantly different performance. Transom angle is important since it governs the maximum tilt setting of the stern drive and consequently the shaft angle.


CAN I TROLL BETTER WITH A DIFFERENT SIZE PROPELLER?

Lower pitched propellers are always best for trolling. The lower the pitch, the better the trolling. Standard propellers with relatively high pitch troll too fast and in throttling down to extremely slow speed, they tend to overload the engine. A low-pitched propeller relieves overloading, permitting the engine to idle faster while moving the boat slower.


WHY DO OUTBOARD MOTORS OF THE SAME POWER SOMETIMES TAKE DIFFERENT PROPELLER SIZES?

This is due to differences in lower unit gear ratios. Stock outboards are geared so that the propeller shaft turns at a slower speed than the RPM at the power head. This is usually expressed as a ratio such as 12:21 or 14:28, referring to the number of teeth in the drive gears. The lower the gear ratio, the larger the propeller that can be used and vice versa.


HOW CAN I BE SURE MY MOTOR IS OPERATING WITHIN THE RECOMMENDED RPM RANGE?

This can only be checked with a tachometer. There are various kinds available and we recommend that every boat be equipped with a engine tachometer.


WHAT IS THE ADVANTAGE OF A STAINLESS STEEL PROPELLER?

Most pleasure boats are factory equipped with aluminum propellers. Aluminum propellers are relatively inexpensive, easy to repair, and under normal conditions can last for many years.

Stainless steel is more expensive, but much stronger and durable that aluminum. If you are looking for better performance than can be provided by your aluminum propeller, such as ultimate top speed or better acceleration, a stainless steel propeller may be required.


WHAT DIAMETER PROPELLER SHOULD I CHOOSE?

This is a popular question for us. Many manufactures develop propellers of several diameters. The propeller diameter is usually decreased as the propeller pitch is increased. This is true in most all outboard and sterndrive propeller applications. Propeller diameter is the total circle that it makes in one revolution. As the propeller’s aft rake is increased its diameter is reduced. The propellers rake and geometry has an effect on diameter, as such we place more value on propeller pitch than that of diameter.


IS A FOUR BLADE PROPELLER A GOOD CHOICE?

Four blade propellers operate smoother and quieter than three bladed propellers do. Generally, a four blade propeller is a good choice for a recreational boater that requires a smooth, quiet and all around good performing prop. The performance of a four blade vs. a three blade propeller is very subtle yet the four blade is a little better out of the hole as well as smoother in operation. Many of our customers find that the four blade performs okay but not great. The only exception is in the bass boat customer that has very specific requirements from their propeller.


WHAT IS THE BEST PROPELLER FOR MY BOAT?

If you are a boater that only requires a propeller that delivers maximum speed and have no concern with water skiing and water sports, than a three blade propeller is a good choice and will perform to your expectation. If you desire a good performing propeller that delivers better acceleration without a significant amount of top speed loss then we recommend a four blade prop. If you desire good top speed and maximum thrust, as well as smooth operation for water skiers, and cost is not a concern then the mercury high five is our recommendation.


HOW DO I KNOW IF MY BOAT HAS THE CORRECT SIZE PROPELLER?

The correct propeller size is one that achieves your boats maximum designed speed while operating within your engines maximum RPM range. There are many propeller styles available to confuse you but it all comes down to this. What propeller achieves your needs? Generally for maximum speed a three blade is your best choice. In some boats a four blade will be a good choice as they perform well and are smoother and offer better acceleration. For boaters that require maximum acceleration without a significant speed loss the mercury high five is a good choice. In summary it really comes down to you and what your expectations and budget are.


WHY DOES MY BOAT HAV A HARD TIME PULLING A WATER SKIER UP?

This is a very common question for us and the answer is very basic. The typical propeller furnished with many new boats today is propped for maximum speed. To pull a water skier or any other type of pulling condition you require more thrust than top speed. This is easily accomplished by reducing the pitch of the propeller, thus increasing RPM and reducing top speed. Usually two inches of reduction in pitch from a propeller is all that is required. Many of our customers prefer to carry on board a prop for maximum speed and a prop for maximum pull.

Note: When operating your boat never allow the engine to operate beyond its maximum rated RPM.


HOW DO I SEND MY PROP TO YOU FOR REPAIR?

To send your propeller, box it and include the following information:
•Name
•Mailing address
•Phone number (Daytime phone number)
•What you need done to your propeller
•Any special questions, concerns, or problems
We will contact you with the cost and time needed to repair your prop.


CAN MY SKI BOAT PROPELLER BE REPAIRED?

We repair hundreds of ski boat propellers annually. It is seldom that a propeller cannot be economically repaired. Send us your prop and we will evaluate it and call you with your total cost (including any taxes and shipping) as well as when you can expect to receive it.


CAN MY ALUMINUM OUTBOARD OR STERNDRIVE PROPELLER BE PITCH CHANGED?

Most propellers can be pitch changed two inches up or down. The propellers blade can only be changed approximately 70% of its blade area. Where the blade meets the hub is unchangeable. A pitch change is not going to be true to what a new propeller would be but is a viable option to correct the propellers load on the engine.


HOW DO YOU REPAIR MY OUTBOARD OR STERNDRIVE PROPELLER?

When we receive your propeller it is tagged with your name and any special instructions for the technicians. Your propeller is assigned a control number to assure that we repair and return the propeller you gave us. Next your propeller is straightened and pitched using a pitch block. A pitch block is a precision machined dye of your propeller, which allows us to correct the pitch, rake and track of prop. Next the prop is glass beaded to remove all paint, corrosion and residue. After your prop is clean it is off to the welding station to weld back any missing blade area. Once welded, the prop is reshaped and excess weld is removed. It is at this point that your propeller is balanced so that it operates smoothly and quietly. As a final step your propeller is primed and painted to protect the metal. Stainless Steel propellers are repaired much the same way except it is polished back to a high mirror finish.


IS MY OUTBOARD OR STERNDRIVE PROPELLER REPAIRABLE?

In nearly all cases a damaged propeller can be repaired. Often what the customer feels is not repairable is. Tacoma propeller repairs thousands of propellers annually. Send your propeller to us and we will evaluate it and call you with a guaranteed price and time it will take to do so. You can expect your prop to look and function as good as new when repaired by us.

 

ZINC ANODES

DO ALL ANODES FIT EVERY WATER ENVIROMENT?

The answer is no. Throughout the world you may find many different water environments which may all require different solutions. The three main water types are salt, fresh and brackish. Zinc and aluminum anodes protect very well in salt and brackish where magnesium anodes protect best in fresh water. Whenever possible, measure electrolytic corrosion around your boat by using corrosion test meter. This will quickly indicate if your anodes are providing adequate protection. A special note on magnesium anodes for fresh water.

Essentially, fresh water is much less conductive environment than salt water, therefore magnesium anodes are you best choice as they are much more active (less noble) than zinc or aluminum anodes. The result is increased efficiency thus superior protection for your underwater metal components.

NOTE: It is not recommended to use magnesium anodes in salt or brackish water. The result may be an accelerated corrosion rate, which may damage the metal parts of your boat and leave you with no anode protection in a short period of time.


WHAT IS ELETROLYTIC CORROSION?

When two dissimilar metals are electrically connected and submerged in a solution or electrolyte a natural chemical reaction takes place. This chemical reaction forms a circuit where the least noble metal (the anode) will begin to break down leaving the most noble metal (the cathode) intact. For example, a sailboat may have many metals electrically connect in salt-water solution. The stainless steel propeller shaft is more active (least noble) than the bronze propeller. In this case the stainless steel propeller shaft will naturally begin to breakdown leaving the propeller intact. Since propeller shafts are expensive to replace it is easy to protect these metals by adding a zinc collar anode to the shaft. The anode is highly active and will corrode instead of the other metals it is electrically connected to.


WHY USE ANODES?

The protection of the underwater metal parts on your boat or motor from corrosive electrolytic action is a very real and necessary concern. The use of an activated alloy such as an anode will help. Anodes will distract the corrosion action to itself and away from expensive metal parts. Fortunately anodes are relatively inexpensive and readily available. Factors such as warm water temperatures, polluted water and stray current corrosion can cause your anodes to waste away at an accelerated rate so it is wise to check them on a regular basis.