Re: Please help!! Propeller fell off in lake & don't know what prop to replace it wit
Re: Please help!! Propeller fell off in lake & don't know what prop to replace it wit
Props are described, primarily, in terms of diameter and pitch. There are some other characteristics of props that are considered, but let's start with the basics. A local marine dealer or an online prop shop will know what selection of props is available for your motor. With a description of your boat and how you operate it in terms of load, they can make a general recommendation concerning pitch.
Think of pitch interms of gears in the transmission of your car - the higher to pitch (measured in inches), the higher the gear. The difference between your car and your boat, however, is that your boat has only one "gear" (prop pitch), so you have to pick a pitch that will work for starting from a dead stop, cruising and running wide open. The trick is to select one that gives a reasonable compromise in terms of performance in each area, as compared to the others.
My suggestion is to try to buy a prop locally, if you have no idea what pitch prop was on the boat previously. Give the dealer the info on your boat and how you operate it, ie: do you normally carry a light load in it, medium load or heavy load. Tell him also if you use the boat to water ski, wakeboard, etc. From there, ask if you can try a few used props until you find the one that works best for you. At that point, you can either purchase the used prop, or buy a new one from the dealer.
Next on the list, is to know the OMC's recommend rpm range at "wide open throttle" (WOT). Every engine has an rpm range, within which it should run at WOT. For example, if your motor should run between 4,500 rpm and 5,500 rpm at WOT, you want to pick a prop pitch that will get you pretty close to 5,500 rpm when operating the boat in whatever load configuration is normal for you. The dealer will try to help pick the right pitch, but may not get it exactly right the first time.
You will want to get close to the top end of the WOT range, if not right at it, with your usual load, so that if you put extra gear or another person or two aboard, you still stay above the lower end of the WOT range. If the first prop you try doesn't get the WOT rpm to where it needs to be, make use of a general rule of thumb that says that each inch of change in pitch will result in a 200 rpm change at WOT. So, if the first prop puts you at 5,900 rpm, try a prop that is 2" higher in pitch. If it puts you at 5,100 WOT rpm, go down 2" in pitch.
One more very important issue - I don't know your engine specifically, but many OMC outboards with thru-the-hub exhaust type props (like yours) have a thrust bushing that fits on the prop shaft, ahead of the prop. My guess is that your motor requires one and since it is slip fit onto the propshaft, its probably missing too. Failure to replace the thrust bushing will cause the spinning prop to ride up the prop shaft, until the hub hits the hub of the gearcase. Should this happen, you can pretty much guess the end result.
Also, don't forget that you will need a new castle nut and spacer too.
