[willy]

Kamikaze that was the problem I had and the reason I pulled the motor and cut the riser plate and drilled new holes for the Armstrong Bracket. I can't snap a photo for you as I don't have a digi camera but I can give you the info.
If you run that straight edge (2x4) along the keel line and extend it out my cavitation plate was 6 3/4 " above that line. No F'''n good, when I would try to trim the boat in a chop at speed I would ventilate the prop, and forget about cutting a hard turn trimmed up at all.
So I spoke with a couple of people that install them and I also spoke with Armstrong twice and they were all very nice and honest. The " ideal " height is 3" above that line and I was double that.
Here is where it gets tricky, some installers feel that is too low and if you are running a heavy V6 motor or a heavy 4 stroke you want to mount the engine a couple of inches higher. Reason being sitting at the end of that bracket there is a lot of leverage pulling down with that much weight and every boat handles that weight differently. On some boats the engine is riding real low in the water even under power and when they back down on the accelerator or are in a heavy chop the engine gets dunked quite a bit.
There are a couple of fellows on this site that have commented on how they hope their cowling is well sealed because their motor get wet a lot.
On mine I found out that I can drill new holes and relocate the engine down, the only problem was the riser plate you bolt to had an extension area on top that prvented the engine from going any lower. So after getting approval from Armstrong ( they have to cut it themselves sometimes) I crossed my fingers and measured it all up 5 million times and and was able to cut it down 2 7/8 " and have clearance to fully raise the engine etc.
The result well if I am trimmed up and try to go thru a chop and bank turns I can still get it to ventilate a little but I just have to trim down a little and I'm OK. On a straight normal run in any kind of water condition I can now trim up and go, no problem.
How your boat sits on the water with your engine is an important factor (check your waterline) Mine has a 115 Johnson on it and sits perfectly level (scupper drains two inches above the water) So I am probably 1/2 to 1" too high still but my engine is well out of the stream and never gets dunked.. If I repower some day with a heavier engine I will probably be sitting perfectly. Come to think about it I have just added a 25 Lbs kicker bracket and a 77 Lbs. 9.9 engine on the back so I am probably a little lower already. I will find out soon and let you know, that extra weight might take care of everything.