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Finding the Right Propeller for your Boat

Unravel the Mystery

Whether you are in the market for a new prop, replace a damaged prop, or maybe you think it is time for a change, choosing a prop largely depends on the type of boating you do. To dial-in a proper choice, several elements need consideration.

For the novice or relatively new boat owner, it is important first to understand that a propeller is the only thing that propels your boat forwards or backward. A propeller affects the speed of your boat, fuel efficiency, pick-up, and overall boat performance whether you have a 2hp or a 2000hp. You could be missing out on great and peak performance with a wrong propeller choice.

Because there are many factors and it can be complicated calculating the right prop, we have made it easy to narrow the choice.

First, you may want to try the Mercury Marine Propeller Selector link online. Based your answers, the program will recommend a propeller(s) type for your situation... or least get you close.

Then there are those special circumstances where it is best to get advice from an expert.

Jim Merten Jr., president of Merten Marine Ltd, has spent a lifetime working with propellers and assisting customers in a variety of situations. He has spent hours and hours of independent research and developed a theory targeting propeller performance that has helped boaters around the world. Many of his successes have been in racing with several national championships and world record breaking titles as part of his list of accomplishments.

By completing Merten Marine's propeller advice form is another great place to begin narrowing the search for the perfect fit. Questions in the propeller advice form are the same basic answers needed should you inquire by phone instead.


Water Conditions

Fresh or salt water, running mostly in rough or flat water, knowing these elements will help in determining a direction for a prop selection.


Water-skiing or Tubing (pulling a load)

Preferably you want a prop that will pop a skier or tuber on-plane quickly and give the best throttle response for when there is slack in the rope. You can reduce your boating frustration by having the right prop on-hand for what is supposed to be a fun vacation or enjoyable family outing.


Fishing, you say?

The style of fishing will make of difference in a prop selection. A few examples are:

Bass boats tend to operate at a much higher speed. They likely fish in places where it is real shallow and their ability to get up on-plane quickly is needed. The ability to travel at a high rate of speed is important because they usually travel the longest distance when they are out fishing compared to other style fishermen.

Most of the operators will have a prop that will surface drive, which means the tips of the blade will break out of the water. This situation allows the boat to run at a much higher speed with a much higher pitch. It is similar to driving your car in overdrive versus being in second or third gear. There are a lot of geometric changes in the blade that allows this to happen based on the material. As a rule, stainless steel props are designed best for that purpose.

Walleye fishermen tend to have much deeper, larger boats because they usually travel on large bodies of water. The propeller should be designed to run in rough water to carry the boat more smoothly.


Non-Planing Vessels

Many people operate pontoon boats, sailboats, trawlers or other non-planing vessels compared to planing boats and again is subject to another set of rules to determine the best fit propeller for the activity.

For instance, a sailboat requires its engine to push a great deal more weight, and at a slower rate of speed, than most boats cruise at. This situation requires a very low pitch propeller and blades that can fold back for less water resistance when sailing.

With a pontoon boat, like other watercraft, you need to operate the engine at its proper RPM, but a special situation happens with a pontoon boat. The wake from the pontoon will verge together and at a certain speed it will converge together right where the gear case prop is. The result is it will cavitate your engine out and you can have a whole bunch of throttle left and no gain of speed. We certainly have props that run great in those kinds of conditions.


Boat Set-Up

If you are running multiple engines on your boat, and whether they are inboard or outboard engines will affect the prop or props suitable.


The Prop is your Transmission

Boat engines do not have a transmission like a car.Although the prop behaves like the transmission; it is also like the tires on a car. Your boat engine has a certain operating RPM band that it needs to run in. If you got a four-stroke engine and you over-prop the engine where you do not have enough RPM, you can burn your valves. If you have a two-stroke engine, you could pre-ignition and burn your piston. On the other hand, if you do it the other way, you prematurely wear out your engine.


Summary

It is my observation that there are very few dealerships that truly understand the propping world. I come from the design end. Mathematically, I can determine the optimum pitch for you. The basic information I begin with acquiring from the customer is your propeller pitch, RPM, your gear ratio, and your speed.

From that information, I can figure out the slip factor. If you have a 20-pitch prop in a one 360-degrees revolution, that prop should screw itself through the water forward 20 inches. The distance that it does not travel is called slip.

Certain percentages for the certain different type hulls is also used in determining correct prop. Not only does the prop control your speed, but the prop will also control the quality of the ride of your boat depending on what kind of water you are running.


Basic Props and Repairs

Purchasing an entry level aluminum or stainless steel prop will do okay. They do not do anything particularly well, but they do not anything particularly bad. They are very basic and not designed for something very specific that you may want to do with your boat.

Both are repairable, within reason. Aluminum propellers are a softer material and the repairs are quicker compared to stainless being a harder and heavier material.

There can be a difference in the quality of repair between prop shops. Some prop repair shops will take the extra effort to weld, grind, and balance the repaired product back to the manufacturer original dimensions. Others will just grind out the nicks and that is it.

Buyer beware, those prop shops might get-a-way with that once before you see a loss in performance.

Prop repair prices can vary as much as the props themselves. If you are a price shopper stay with aluminum. If you are a performance-orientated person, stainless props are a better option.