The water is so turbulent under that foil during take off I doubt there is a bit of difference. I run mine (300R) on top, it sure looks better, even though they are much harder to get in due to the hollow anti ventilation plate on the sporty. In fact I had to drop my lower unit down to get the two bolts most forward to go in. JMO. Thanks for the reply.Originally Posted by TheRubberDuck
Edit: Adding some information for clarification and accuracy. First of all there is no cavitation or anti cavitation plate on an outboard motor. Cavitation occurs when the pressure on the low pressure side(front side) gets low enough to cause the water to boil. This will cause blade slip and pitting of the metal on the blade surface. This would be an exceedingly rare event.
What you do have is an anti ventilation plate. Ventilation occurs when the prop is pulling air from the surface (and or exhaust) causing the prop to slip. The anti ventilation plate "shades" or blocks some of the surface air lessoning ventilation. When you add the foil, even though you are getting a little lift from the angle of the foil, the main thing you are doing is increasing the effectiveness of the anti ventilation plate. The higher you run the motor the more likely excess ventilation will occur. Those of us that run the sportmaster with P to P above the pad, some approaching 2 inches above, have a hard time taming ventilation. In my particular set up (XRS and 300R) I had to lower my motor from 1-7/8" above to 1-1/2" above. I was getting tired of slinging blades and struggling with ventilation a little. Mark Croxton strongly suggested I lower the motor and give up a few MPH to help prevent ear slinging.
To the OP: If there comes a time you tire of seeing those multi colored balls in your jackplate, I have an alternative method. You will need a top plate also for my method. Go to Lowe's or similar and buy a pack of 1"x12"x48" styrofoam boards. You can cut this up into appropriate size pieces and fit them into the jackplate. You will have to cut foam into pieces you can fit under and around the rods and nuts but, with a little effort you can stack it one layer at a time to completely fill the jackplate. Add the top plate and you have a neat installation that is out of sight and you get rid of the clown look of the balls, no offense intended. Feel free to PM if you need more information on the styrofoam installation.
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