Physics of a prop?

[waltherbey]

Being a novice please forgive my lack of boating knowledge....<br />I am just wondering why a prop with a lower pitch gets a boat out of the hole quicker? <br />If a higher pitch relates to a longer travel distance of one prop rotation then doesn't that mean a higher pitch will push more water?<br /><br />I am guessing that a lower pitch number will allow the engine to gain RPM's faster and therefore get into the power-band sooner....<br /><br />Is this true? or maybe someone can explain it to me.

 

[Ginder75]

Re: Physics of a prop?

You seem to have the concept down. No different than the gears in a truck. The lower 5.15 gears are great for climbing rocks and bolders, but they are interesting on the highway.<br /><br />The lower pitch, will let the prop spin up to the recomended rpm's quicker. But once the hull is on plane, the prop will not have enough leg to keep pushing the boat.

 

[Silvertip]

Re: Physics of a prop?

There is no transmission on a boat. It's in high gear all the time so a compromise is required between lower unit gear ratio, maximum recommended engine RPM, prop design, and its pitch. Try starting out from a stop sign with a stick shift car in high gear. You'd likely burn up the clutch after three or four attempts. In a boat, too little pitch causes the engine or over rev. Too much pitch causes it to lug (like a high gear start in a car). There is also a limited amount of power so too much pitch will pull the engine off its power band as you figured. Too little pitch gives a great hole shot but again, top end speed will suffer and the engine will over rev like running that stick shift car wide open in first gear.

 

[walleyehed]

Re: Physics of a prop?

Take a look at this link and see if it helps at all...if it does, let me know...if it doesn't...well...let me know..<br /><br /> http://forums.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000030

 

[waltherbey]

Re: Physics of a prop?

Thanks for the information. It always helps to know what the basics are when playing with a new toy.