"HERE's couple posts in TB
"HERE's couple posts in TB forum---Mercruiser calls it "timing" the props. It's not required on a Bravo 3, but when you have them off, you might as well do it.
"The simplest way to explain it is that when you put the rear prop on, have one of its blades pointing directly up at the anti-ventilation plate, while the forward prop has one blade pointed directly at the ground. The idea is so no two blades pass directly under the anti-ventilation plate at the same time."
"I had some work done on my outdrive last year. I asked the mechanic about timing the props and he said he never heard of such a thing. I read several posts on other boards that would lead you to believe it is a joke like a jug of radiator fluid in the bonnet of your VW bug. Old bug, not new.
Anyway, the props, as he put them on, had the blades passing the cavitation plate at the same time. The boat had weird vibrations all the time while underway. Like it was missing on one cylinder.
At the end of last season, I pulled the props to lube the shaft. I timed them as described above. Not one vibration this year. The boat is so smooth I can't believe it.
BTW, the reason the outdrive was in the shop was because I didn't pull the props to lube the shaft and they were seized on. $1000 stupid tax on that one. I pull, lube and time them every year now.""