Select best prop for your needs

Ironically, it’s the fox squirrels — and not their smaller cousins — that draw hunters to Cat Island.

I have been in the boat business for many years. I know and appreciate the technological advances that have occurred in that time, but I do occasionally find myself reminiscing about the simple good-old days. When a customer recently asked for help in choosing a propeller for his boat, I recalled how easy it was to choose a prop way back then. For instance, if you owned a Mercury engine, you simply purchased a Mercury propeller. I would simply ask if you preferred an aluminum or stainless-steel prop.

As a dealer, I had factory charts that helped determine the optimum pitch for your new propeller, and I made the sale.

Now if you go to your local Mercury dealer and ask for a propeller, he might ask if you would like an Alpha 4, an Enertia, a Mirage Plus, a Black Max or one of 14 other propeller styles in the Mercury arsenal. Mercury actually manufactures 500 different and distinct propellers for their outboard and stern-drive engines.

We can add to the confusion by also considering the many different after-market propeller manufacturers as well as the other outboard motor manufacturers. There are two-blade, three-blade, four-blade and five-blade propellers. These props are made of composite materials (plastic), aluminum or stainless steel.

Of course, each manufacturer will usually claim to have a different alloy of aluminum or stainless steel that makes his product superior to all others. Some have through-hub exhaust; others exhaust over the hub. Some have ventilation holes; others do not. Some are equipped with a rubber slip clutch; others may have a plastic break-away hub, and some do not have any hub.

So how do you choose?

Education is your best friend. Learn everything you can about propellers, their design, function and application. By understanding the different aspects of modern props, you will be better able to sort through this maze and choose a manageable few to experiment with on your boat.

Unfortunately, there is no one propeller that will do everything for you. If you need an exceptionally fast hole shot, you will probably have to give up a little top end to get it. If you want heavier load carrying ability, you may have to sacrifice hole shot and top end. Some wheels can give you smooth acceleration and reduced vibration, but you may have to give up something else in return.

You can start by defining exactly what you want from your boat and motor combination. If you are a weekend fisherman who carries a normal load of two or three buddies and gear, you may not be interested in blazing top-end speed. A safe, comfortable cruising speed with great fuel economy and a decent hole shot to get you out of those shallow-water spots may be just what the doctor ordered.

If you have kids and they like to water ski and tube, then a little more hole shot is in order.

Maybe your boat is a little larger and you go back and forth to the camp carrying everything but the kitchen sink; then you will need a prop designed to carry heavy loads.

Some of you may fall into two or more of these categories, and if you do you will need to carry alternate propellers so you can swap back and forth as needed.

In order to better understand propellers and the job they do, it will be necessary to study several terms and definitions. The first: What is a propeller? I like to think of a prop as a form of screw. As a matter of fact, marine propellers are often referred to as screws. As the propeller turns, it exerts force that is used to push your boat across the water. This is almost the same as a screw threading into a nut. The type and design of that screw will determine the application it is best suited for.

Your propeller needs to allow your engine to achieve the optimum-rated RPM as set by the engine manufacturer (refer to your owner’s manual). You do not necessarily have to get the highest RPM in the range. It is usually best if you can reach the middle of the range. If you select the wrong prop, you may not only reduce performance, but you could seriously damage your engine.

Unfortunately the only way to determine the best propeller for your boat and boating application will be through experimentation on the water. Keep in mind that when you go to the lake for testing, you want to do so with an exact duplication of what your normal load will be for your boat. If you are normally cruising with the wife and three kids, then take them with you to conduct your tests.

Back in the old days, you would simply choose from two or three propellers, hook up your boat and gather your normal boating load of persons and gear, and head out to the lake. Armed with the knowledge of your engine manufacturer’s recommendations for max RPM operating range, you would begin to try the wheels that you brought. You would try one wheel at a time until you found the one that allowed you to achieve the engine’s recommended max RPM with your normal load in the boat.

You may be tempted to stop here and do exactly as I just described to pick out a prop for your boat. If you do, you may get lucky and find that perfect wheel, but maybe you won’t be so lucky.

If you would like to learn more about propellers and prop design, check my column next month. By examining propeller design and defining terms such as pitch, rake, cup and many others, I will attempt to take some of the mystery out of propeller shopping. The more you know, the easier it will be to find the best prop for your application.