picked up a bracket
 

Edit

Well alright, looks like I'm winging it.

From what I found on my 20'bracketed seacraft I ended up at 3.5" above the keel with a 24" setback so it sounds like you will be about right with where you are planning to be. I started out and tried some different heights and ran as high as 5" with a simi-surfacing prop. At 5" it was squirrelly feeling and slipped when I trimmed up too high. It needs more than the +1" inch per foot rule so a low starting point of 2.5" is good and you will go up from there and find out between 2.5" and 3.5" is best for the 20'. I would try to mount the tub as low as possible too, that will give you more flotation at rest which you will need along with moving weight forward to regain balance. The weight of the bracket moves CG too far back.

bracket
 

Could be the picture but the angle does.not look correct... Is the top of the bracket parallel with the keel..

It's just a plywood template to get the mounting holes of the bracket and the engine height aligned. The line if the ply wood isn't the top of the bracket

Thanks frizz for the input

I don't see a picture.

He deleted the pic and the post he made, just says edit now.

Hope he wasn't offended by my comments

Hey Friz, that 20 bracket,was that the one you built , modified from a dusky bracket.. If so, do you know the weight of it...the bracket I build for my 20 is a little heavy compared to others here whom built there brackets... Mine is around 185lbs. I too need to know where to mount especially at the weight.. I am running a 120 looper johnny. Thanks

Yea that's the one, I made the swim platform mold and cut the top half off of the dusky bracket and modified it to look like a more modern bracket. If I remember the dusky bracket was 210-230 lbs to start with (twin Bracket). It had 3/8 solid glass outer skin with a 1/2" balsa core with a 1/4" of glass on the inside of the cored tub. The tub was a 1.5" thick with the balsa core in it and that was the entire tub except the back that had two 3/4"plys for the motor mounts. Some places were 1/2 thick. I believe after cutting most of the weight off that I could and added the swim platform back it ended up being around 180-190lbs. A lot heavier than I wanted but it still works very well. I forgot to put the plug in it when I unloaded at the ramp and the platform sat down in the water 2.5"- 3" lower in the water with the lower lip almost touching. So the floatation value helps a lot. I sat it low as possible, all the way to the bottom of the keel low as possible with outward 3" mounting flanges instead of inward flanges like most made the tub about 3" up from the keel. The one I am building now for the 25'seafari will be 2" up from the bottom of the second steps of the bottom. The lower the better but I think you need at least the 2" so the water will not drag on it and cause issues and also a little angle upwards to the rear if that low. I tub on 20' came all the way out to the third step almost so there is more flotation value than some other flotation brackets like Armstrong's and it being a twin bracket converted to a single made it have a lot more volume. I calculated the air space one time and it was enough that it floated its own weight but that was about it but like I said before that was almost a 3" difference in height at the rear in the water.