I will share my plans for my Hallett 20.5'. For you, I would recommend not going with a full setback though.
First, if you are going to the expense of doing the bottom, the jet install needs to be the very best it can be or it is just wasted money and effort. If you have a 3-point motor mount system, you will need to go to a 4-point or rail system.
For most, I wouldn't recommend a full setback. The twisting and pounding the hull experiences in rough water will crack the epoxy faster in a full setback. A race boat doesn't experience these conditions and is not really an issue. On a boat that might experience white caps, the durability will be reduced. If you want to be hard core and doable full setback, you need to regularly inspect the intake and not be afraid to reset it when the epoxy cracks.
I would trim the transom wood behind the intake and cut the opening back to 1" from the inside of the transom fiberglass. Take this time to machine the intake for a shoe and ride plate. The flang at the rear of the intake can be shortened to half way through the two rearmost holes, to get the intake as far back as possible.
Add glass to the area at the rear of the intake in front of the transom to make it flat for the intake to sit on. This also prevents grinding through the bottom when you grind clearance on the bottom for the ride plate.
When you add glass to fill the hole at the front of the intake, build the glass up and feather it out so that it is flat across the front of the intake. This reduces the amount of Poxy Putty used for the install and makes a really clean finished install. It also provides additional thickness for blending the entry of the intake.
If a Berkeley intake, install it at 4-degrees at the suction surface and as low as possible. Just make sure that the front of the intake opening is not hanging below the keel. Once you have the intake set, only then are you ready to work on the bottom.
That hull should not have any excessive rocker or hook. Only about the last 3-5' is critical for straightness. Remove any hook or rocker by building up with glass. Do not try to straighten it by sanding off existing glass. It is critical that this area of the hull not flex hook into it while on plane. That will scrub off speed.
Next, you can add keel depth in front of the intake. It should be the width of the intake opening (7-7/8") and I would extend it all the way to where the inner stakes meet by the bow. The depth added to the keel should parallel the existing hull front to rear.
The depth of the keel is relative to the speed the boat will run and therefore how much horsepower you have. Too much keel will create excessive drag and it could overcharge the pump. I would probably start with 3/16" to 1/4" with 11/32" max if you are in the 1200+ horsepower range.
The intake needs to be seamlessly blended into the keel. The radius of the intake to tangent point at the flat of the keel should be between 8" and 9" from the front of the loader/rock grate pad. I posted some diagrams in an older thread, that I just can't find right now. Hopefully I still have the drawings on an older PC. If I can find them, I will post them up later.
I will assume that you have back seats and some kind of engine cover. You will want to move the engine as far forward as possible, within those constraints. At the very least, try to get the oil pan in front of the jet intake.
Which hull do you have? Would love to see pictures.
Cheers,
Joe
