I thought I'd share something with you that may really help this situation if it plagues you.

For years the sled I have cavitated when I'd hit slightly rough water, likely removing some amount of life from my engine evertime it reved because it reved quite high at times.

I read an article somewhere... can't locate it now but they discussed the properties of water under extreme pressure and extreme vacuum. One of the problems with water under extreme vacuum is that it develops air pockets or holes when a rapid change occurs from no vacuum to a high vacuum state. In the article they also discussed water flowing over and by sharp, rounded, and flat objects and the difference in water properties as opposed to air properties with regards to flow.

The grates on a jet produce both extreme pressure and extreme vacuum. Extreme pressure on the front side of the grate because the flat surface and likewise extreme vacuum on the backside, well because the impeller is pulling water past that grate like… (use your imagination here).

Ok so armed with the information from the article I got to thinking about the grates on the bottom of my outboard jet. I removed all the plates and took them to the grinding wheel (12” grinder). I formed a rounded leading edge on each plate, which will help eliminate a vortex forming. Incidentally a sharp leading edge can cause flow redirection problems, kind of like harmonic waves. I also formed a knife edge taper on the trailing edge (the edge closest to the impeller) of each plate. This shallow taper will allow the water to slip smoothly past the plate without forming an air pocket on the back side of the plate. Actually the ideal shape would have been a ‘tear drop’ but I settled for a very shallow hollow ground trailing edge. It took about four hours to grind all the material away on the eight plates but I can attest it was worth every minute of the task.

The jet runs noticeably smoother and the cavitation problem I had before is dramatically improved. As a mater of fact while you probably can’t completely eliminate cavitation on an outboard jet I would imagine that I have seen an 85%-90% improvement. Last time out the jet only cavitated three times and when cavitation does occur it doesn’t even spin up more than a couple hundred RPM, because the air pocket is evacuated almost before it develops. I think I gained a little more power too but this is harder to quantify.

Good Luck!

Legal disclaimer - your mileage may vary but it really helped in my case!