Under or Over propped??

[willxuout]

1996 Evinrude 225hp V6 - RPM per bombardier is supposed to be between 5800-6000 rpm WOT.<br /><br />Before the rebuild WOT rpm was 5400. Is this considered under or over propped?<br /><br />would this lugging condition contribute to or cause an upper crank bearing failure???<br /><br />Thanks

 

[DJ]

Re: Under or Over propped??

will,<br /><br />You are OVERpropped.<br /><br />Whether or not that caused your failure, hard to say. It didn't help it though.<br /><br />Overpropping typically adds up to sticking rings due to combustion chamber deposits.

 

[willxuout]

Re: Under or Over propped??

As soon as i am through the 10 hour breakin period on the rebuild i'll need to put another prop on the motor.<br /><br />thanks djohns.<br />

 

[DJ]

Re: Under or Over propped??

will,<br /><br />Remember. A 1" change in pitch is worth about 200 rpm's, up or down.<br /><br />Good luck on the rebuild.

 

[Dhadley]

Re: Under or Over propped??

Perhaps you can gain some with the set up rather than buy another prop.

 

[willxuout]

Re: Under or Over propped??

dhadley,<br /><br />be more specific about "setup"<br /><br />Thanks

 

[Dhadley]

Re: Under or Over propped??

Take a look at the X dimension. Thats where your cav plate is in relation to the bottom of the boat. Anytime you can raise the motor (increase the X dimension) you reduce lower unit drag and therefore gain rpm. Most likely you will gain some speed too. maybe not a lot but some. <br /><br />We can gain rpm by going to a lower pitch but that may decrease speed. <br /><br />The correct X dimension is a marriage between your prop technology, hull design and load distribution.<br /><br />If the motor is mounted all the way down try raising it and see what happens. We can spend money later.<br /><br />Good luck!

 

[willxuout]

Re: Under or Over propped??

dhadley,<br /><br />this motor is mounted on an omc sea drive bracket and is pretty much set permanently in the X dimension. The only cost effective choice i have is to change the prop pitch.<br /><br />right now i get about 40 mph out of a 23' wellcraft (25' LOA). I generally cruise about 30 mph at 4400 rpm. If I change the pitch by 2" the rpm at 30 mph will be about 4800 rpm. Right?

 

[willxuout]

Re: Under or Over propped??

oh, by the way, the cav plate is about 1 1/2" out of the water when on a plane and trimmed out.

 

[rolmops]

Re: Under or Over propped??

have a look at :<br />www.miwheel.com/MIWheel/pdf/obsd_03.pdf<br />This is over sixty pages of explanations and cross references and everything you wanted to know about propellers.