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How to prop your boat


Lets face it, selecting the right prop for your boat can be a tough job if you don`t understand what the characters of a prop are. Props come in many designs and materials, and the manufacturers have the knack of producing big fancy advertisements trying to show their product as being the best. In the following, I will try to disclose a little bit of the mystery of prop design and selection.

Diameter and pitch: Lets start with the diameter and pitch. The diameter of a prop is pretty much self explanatory, but the pitch is sometimes a dilemma to a person. The pitch of a prop is defined as the theoretical distance the boat will travel with one complete revolution of the prop with 0 slippage. Obviously there is slippage in water, but this is the standard in which a prop is built. For example, when someone tells you that a prop has 21 inches of pitch, that means that the blades are set at an angle that will theoretically move the boat 21 inches in one complete revolution of the prop.

Ok, now no one cares how far the boat moves, only how it performs right? Selecting a prop for your new boat is normally made easier due to the fact that most dealers already have pre-installed the prop for you. Lets say that your boat does not perform to expectations though. What do you do? First off, if its a new boat, talk to your dealer. If you have a boat thats been in existance for a while, the first thing to do is check your RPM on the tach at wide open throttle. Outboards can handle, and should run a maximum of 5,500 RPM wide open. Inboards most generally red line at 4,500 RPM. If your boat does not run at or very near these RPM`s wide open, one of three things can be the problem. First, a mechanical problem can exist, second, ambient air temperature can greatly affect the performance of a motor. If its an extremely hot day, performance will drop, thus RPM will also. Third, the boat does not have the proper prop installed. If your motor is mechanically sound, and its an average temperature outdoors, but your wide open RPM is lower than previously mentioned, you may need to go down an inch or two in pitch. If it runs above the specified red lines at wide open throttle, you may need to go up in pitch. Beware though, it doesnt take much to make a difference. Most times, pitch can be reset by a good prop shop, without the need for purchasing a new prop. Two inches up or down is normally the max though.

Designs and materials: Now that I have explained the theory of a prop, lets go to designs and materials. Props come in three materials, and have many designs. Props are made of aluminum, stainless steel, and brass. They all look pretty much the same you say? At first glance maybe they do, but when it comes to the technical aspects they differ greatly. In the beginning, props were made of brass and had only two blades for most applications. This was fine back then, due to the small and lightweight designs of boats. Todays applications require more bite to push to carry the load. Therefore, props with 3 blades are most common, but 4 and 5 blade props have been introduced. 3 blade props provide the best all around performance and good top end speed. 4 and 5 blade props are used for alot of bite for low end take off and to get on plane quicker, although they limit and usually reduce top end speed. For all around normal performance, an aluminum prop is probably best suited, and run from $60 to $200 depending on your application. If you want higher performance with your boat, consider upgrading to a stainless prop. Manufacturers claim different advantages of their prop over others. This is sometimes true, and sometimes just a sales pitch. Some claim higher speeds simply by installing their prop. There are a few out there that will do just that. When it comes to speed, the greatest affect comes from a couple of different things. Weight, horsepower, hull design, and lastly the prop design. If you have the power and good hull design, the prop can make or break your complete combination. For all out speed, choose a 3 blade polished stainless prop that has good cup to it. These run anywhere from $350 to $600, and will give you a good low end holeshot, and decent top end speed. If you dont mind emptying your pocketbook a bit, you could also consider a "shift prop". A shift prop? These are a fairly new design, and do exactly what the name states. They are a mechanical type design that use springs to determine when the blades pivot to change pitch. At idle and low speeds, the prop is in the lower pitch range, and at a higher RPM, the blades pivot to a higher pitch range, feeling just like a shifting transmission. The RPM that the blades pivot is determined by the spring setup. This is about the only way to have the best of both worlds, an unbelievable holeshot and outstanding top end speed with one prop. These get pretty pricey though and can run as much as $900. If you need help or have any questions about selecting the right prop, just send us an email, and we will help you all we can in making the right choice.