jack plate question

Hello, I am new to the boating world and have bought a 17' tracker grizzly for fishing and some duck hunting on my local lakes.it has a 75HP merc with a 13X21 stainless three blade prop.I am having alot of porpusing if i try to run more than 50% throttle,i know this seems to be a common problem with this style of boat but i wanted to know if I might cure some of it if not all of it with a jake plate.I have my motor at its lowest mounting hole and have added one of those lower unit fins(helped very little) but still feel I need to lower the motor but cant, I read somewhere on here that If you run a jack plate you can run your motor higher so i thought it might help.I had a friend run the boat about 75 percent with it trimmed way down to control the bouning and I looked over the back at the motor and the cavitation plate is running just out of the water,is that the correct height? and with the motor trimmed all the way down the plate is still higher than the bottom of the boat.
any suggesttions would be great,I am not trying to make the boat really fast or anything just want to be able to run a little faster without having to trim the bow down so far that is draggin and pushing through the water like a barge.
thanks to all the reply.
Jared

 

what about trying a transom wedge??? to rake the motor about 5 degree

 

Angle

The motor needs to be trimmed. I expect you dont have electric trim so you'll have to set it at a different angle to the bottom of the boat. Wedge or electric trim.

 

Want to put a jet drive on my 90hp suzuki 4 stroke, the hull is a new Carolina Skiff 21 foot flats boat. Is a jack plate needed and also, what setback and type. Any help would be appreciated.

 

The cavitation plate should be touching the water. It produces a bit of lift and helps prevent porpoising a bit. If it is above the water, even a small amount, there is cavitation. Also, if it goes in and out of the water and produces lift on and off, it will add to the porpoising.

 

The plate above the prop is there to stop the prop from sucking the water down from the surface at high rpms. Running in gear or tied to a dock and reved up in gear. Prop slipage in gear while tied to the dock is called "ventilation" and you will see the whirlpools of air go down to the prop and hear it race up. Lower the drive until it stops sucking air down.Then you can see if you really have a "cavitation" problem.

 

Bob's Machine Shop in Tampa. He has fixed and Hydraulic. I have a Hydraulic one on my boat and it works out well. . In fishing the flats these come in real handy. As for the cav plate this should be at the further most bottom of the transom.

 

OOOooo!OOOOooo! I saw something cool the other day!! I forget what they're called, but they are flat plates that extend the transom below the hull bottom (not much, maybe an inch at most). This actually produces a hydraulic wedge under the hull with less drag than a trim tab or an ordinary wedge. Sorry....I like to share

 

I think that Thunderhead is describing the Volvo QL Boat Trim System.

info at:

http://www.qlmarine.com/ql.asp

(the web page has an internal frame, so you have to select "Boat Trim System" once you're there)