jack plates and positioning

first time poster and i need help.ive done reasearch but cant find any concrete answers. ive got a 16/48 semi tunnel hull jon boat.im having trouble planning and alot of drag.from what ive heard my ventalation plate need to be level with the top of the tunnel,mine is about 3'' below.i cant raise my motor any more without something addedon so i found a decent priced manual jack plate at bass pro but i need to know if i use the jack plate the motor will set back 4 in. doesnt that now change my motor position or do i still mount it with the plate level with top of tunnel? thanks for any help

Let me first say that my response is based on the assumption you are running a prop, not a jet.

There is an old saying that for every inch of setback, you can raise the motor 1/2". However, I'd start with the cavitation plate level with the top of your tunnel and test. Try some hard turns and make sure there is no cavitation. Also make sure that water is exiting through the indicator. If all goes well, you can bump the motor up in 1/4" increments and keep testing. you may also want to look into a tach if you are going for the absolute fine tuning. Good luck.

yes it is propped and not relly tryin to fine tune it just want it to work the way its suppose to.right now it is really hard to get on plane and until i bought this boat ive never heard of a tunnel hull so this is kinda new to me.not sure if anyone is familar with the specefic jack plate im getting (mini jacker from bass pro) but with it bein a manual it only has so many adjustments.is there any reason i would want to be lower than level with tunnel? just trying to figure out where to mount the jack plate

I believe the mini jacker is technically not really adjustable, but it does have several hole locations. Start out with the cav plate level and bolt it on and try it out, if you are happy then go back and add some 3M 5200 to to bolts to seal it up. If not, make the needed adjustment.

The only reason you'd want it lower than the tunnel is if you were having problems with it level. The higher the better IMO.

ok thanks and just curious im tryin to picture it set up.do you think i will have any problems with water pickup with the plate level like that?

I have that jackplate on my boat. If you mount it even with the top of your transom it is a 3" raise. I would go ahead and mount it there for starters. That would put your cavitation plate even but you should still be on the safe side because of the setback. I might be wrong but that is my opinion.

I just put a plate on a similar boat (prop tunnel, 14ft mod. V). Mine can't be adjusted and I raised it 3" straight up from the existing transom. It absolutely flys now with a 30 hp on the back. I did have to play around with trim setting a bit. Only thing I would say is that with the anti cavitation plate even with the top of the tunnel is if I have someone sitting on the front casting deck she takes a little before the prop bites (or I would have to manually trim it lower which its a pain moving that pin). With your set back you shouldn't have that problem tho..