Prop questions

[msk500]

I have a '73 Mercury 850, 85 hp. Currently it has a 21 pitch prop.<br /><br />I've read a lot of posts about WOT rpms and choosing your prop at least partially based on this. If however you don't plan on running around at WOT and you're satisfied with your holeshot does it really matter what prop you have, within reason, if you plan on running at 3500-4000 rpm?<br /><br />Also, I have small pits, about 3/16ths diameter on the forward side of my prop down where the blade attaches to the hub. What would cause this?<br /><br />Thanks

 

[Jack Shellac]

Re: Prop questions

Those pits are probably caused by cavitation. The pressure on the front of your prop is getting near a vacuum and the water is boiling. As the water vapor bubbles collapse, they chip away at the metal. Causes of cavitation can be nicks, too much cup, sharp leading edge corners or poor blade design. <br /> Regardless of whether you run wide open, your motor will lug if you have a prop with too much pitch keeping your WOT RPM's down. You really need one that will get you in the upper quarter of the RPM range. Your motor will perform better and last much longer.<br /> Welcome to the forum. Hope you find this useful.

 

[msk500]

Re: Prop questions

Thanks

 

[LubeDude]

Re: Prop questions

I also welcome you:<br /><br />Jack has nailed your question pretty well. However like you said, if you like your hole shot and you are at least proped where your engine will reach max RPM (or more), you would be ok to leave it alone as long as you do not over rev. There are lots of Bass and ski boats that are propped with lower pitch props for the hole shot, (pulling power), just watch your tach. Like Jack said, you just do not want to lug it.