Whatever gunny says, he's THE boat guy IMO

You want the antiventilation plate .5" to 1" above the bottom of the keel when motor is tilted level to match a level keel. This can be a general baseline.

Same applies for top of the tunnel. Then can start to tweak for performance and shallow water ability.

What kind of hull do you have? If you need to raise it higher look at a low water pickup like Zephyr Cove Customs.

The fact that you have the current 25" motor mounted with the bottom bolt holes and the plate is all the way up, Im thinking a 20" with it bolted lower, should be perfect. Do you ever take it in bigger seas? Could result in some cavitation when traversing larger waves but hard to say for sure. Inshore, you'll be a lot happier.

The 20" shaft will definitely help you to idle shallower. Part of your problem is that 10" Bobs jackplate. It's a common setup for improved performance, but it moves the heavy motor further back which results in more squat at rest or low speed. Good for speed and MPG but bad for idling shallow. I prefer a 6" but its probably not worth changing at this point. Your's is also setup with wedges which add even more set back.

What brand motor are you putting on? If it's a 225 suzuki, that's a big heavy engine. It's going to make your boat squat more than it does now. If you want to stick with suzuki, I'd go 200 I4. Or Merc will save you a bunch of weight in the 225. The new v6 mercs are known for being able to run an inch higher than most motors.

ETA, do you know why the wedges are on there? Typically used for faster planeing or if you're having trouble keeping the bow down at speed. Might be able to remove them with new motor.

Howdy. Was at a long meeting tonight and just got home and saw your post.

The Blazer 2220 GTS is spec'd to have a 20" transom height and therefore should have a 20" shaft engine. This would be called a "Long Shaft" in industry terms. 25" shaft engines are called "Extra Long Shaft".
Blazer allegedly had some performance issues with the 2220 GTS (It would cavitate and blow out coming on plane and sometimes cavitate in heavy swells) So, as a remedy, some dealers started rigging the 2220 GTS with 25" Extra Long Shaft engines. They would then use hydraulic jack plates with large set back dimensions (like the 10" Bobs on your boat) and mount the engines all the way up on the bottom hole....and raise the jack plates all the way up to get as much as possible of the lower unit out of the water, to increase top end performance that they were loosing from the extra drag of the 25" shaft engine. Very counter productive.

The offset, (Or "step" as you are calling it) is actually in correct terms called a water flow foil. It is on the bottom of your transom, it is designed to allow water that is coming off the primary pad or running surface to rise up faster, (for lack of better terms) and allow higher engine height settings...which gives less drag and increases top end speed.
Sometimes dealers and/or consumers add an additional after market set back plates of various dimensions to enhance the above effect even more.
The additional set back typically will allow the engine to have a better "leverage" or better "lift" to give better bow lift which can oftentimes increase top end speed.
However there is always a trade off when you do that.......moving the engine back also moves the boats center of gravity back. This can slow down how fast the boat comes on plane, (called "hole shot"), increase how high the bow rises when its coming on a plane, cause the boat to porpoise at slow speeds and cause the boat to have ill handling characteristics in turns. So even though you may increase your boats top end speed by having a greater set back distance you typically hurt its performance in all the ways I just described.
Now lets talk about jack plates.....jack plates are made to raise the engine straight up or "jack up" the engine...hence the name "jack plate". Why do you want to raise the engine up? Two reasons...1.) By raising the engine up you get more lower unit out of the water which decreases drag and increases top end speed.
However, to get the full benefit of raising the engine up you need to use specific props designed to have their blades "surfacing"..but still able to have sufficient "bite" to hold the water well and not cavitate.
2.) To be able to run in more shallow water.

So, to summarize, it is important to understand the advantages and disadvantages of a "set back" and how to properly use and gain the benefits of a "jack plate"....and the differences between horizontal set back and vertical lifting by a jack plate.

If a boat hull is designed correctly it should not need an excessive amount of "set back" to make it perform correctly. I question the need and or advantages/disadvantages of the large set back your boat now has on it.
That much set back may be hurting your overall performance rather than helping it.

The other issue is why it has wedges installed on the plate? These wedges are are allowing your engine the ability to have about 5 degrees of additional "under trim". This is usually done to stop porposing at slow speeds and to improve hole shot...which is aggravated or caused by having the large set back plate distance...which typically actually causes porposing and poor hole shot.

With all that being said, understand that I cannot give a definitive accurate assessment of your set up without seeing the boat in person and actually running it. With solely what I see in your pictures, it is just my best guess, summation/opinion that the 25" shaft engine, the large set back plate dimension, and the wedges all have been added to for a performance reason. Again, I would have to actually see the boat and run it to be absolutely sure.

As far as the correct engine height, on a correct set up, I would start by mounting it on the 2nd hole up on the jack plate and adjusting the jackplate vertical height as needed.....Start with the plate all the way down, and trim at full undertrim. Then put the boat on plane and adjust the trim amount and jack plate height for the best performance.

Gunny, this is gold. You are a treasure to a newer boat owner/captain.

Not to derail, but can you educate me/us and expand on the downsides of "setback" of the motors in the context of a boat/hull like the Regulator 26 that mounts it's twin engines on a giant bracket off the transom. I was told that it's there to make it ride like a 30-32 foot boat, I was never told there were downsides. So, isn't that giant bracket the ultimate example of extreme set-back? Why did they do that with the Regulator, and why doesn't it have the performance issues you're describing?

Disclaimer - I've fished a lot of hours on my buddy's 26 but it's an inshore/offshore boat with twin 250s and without jack plates.

Gunny456 said:

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Blazer allegedly had some performance issues with the 2220 GTS (It would cavitate and blow out coming on plane and sometimes cavitate in heavy swells) So, as a remedy, some dealers started rigging the 2220 GTS with 25" Extra Long Shaft engines. They would then use hydraulic jack plates with large set back dimensions (like the 10" Bobs on your boat) and mount the engines all the way up on the bottom hole....and raise the jack plates all the way up to get as much as possible of the lower unit out of the water, to increase top end performance that they were loosing from the extra drag of the 25" shaft engine. Very counter productive.

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I never cease to be amazed by what some manufacturers and dealers will do when rigging a new boat. All of that rather than just making a prop change that would probably fix it. It seemed odd to me that OPs boat had wedges but he purchased new and didnt seem like he would have been involved in the decision to add them. Meant someone was searching for an answer before he even got the boat.

Such great info and explanations. I love boats.

Dr. Boogs.
Here is a simple basic Aggie drawing of the concept of how a set back works. You can see how…by moving the outboard back allows cleaner water to the prop and also allows higher engine running height.
This set back can also be built into the hull mold itself or as a bracket. If the hull is actually designed for it, it works really well.
The main thing to grasp is the fact that the water flow goes up at an angle once it leaves the running surface.
Hope this makes sense. My drawing greatly exaggerates the flow angle going up but I wanted to illustrate how it works….and how you are able to raise your engine much higher.

We need to save this thread, I have learned more about how outboards are setup (and why they do it each way) in 30-40 min of reading and re reading this thread than I've learned in 20 years of owning shallow water fishing boats. Gunny, Good stuff and thanks.

I'll try to answer each of your questions best I can:

1.) Yes. The TRP dual counter rotating lower unit eliminates all "P-Factor" ..therefore no steering torque. It also creates more horizontal lift of the entire hull lift....not just bow lift.
2.) Yes. Pure tunnel hulls will be much slower than convention hulls. Pocket tunnels are not quite as slow as full tunnels. Tunnels designs, pocket or full, do not turn real well.
As you say its a trade off.....tunnels are not near as fast as conventional hull designs but they can run really shallow of course.
Another thing that greatly affects shallow water capability is weight. That's why all the performance flats boats are so very light. Weight equals speed....the lighter you make a boat, theoretically the faster it can run.
Its just physics and simply a weight vs horsepower ratio.
3.)Props are very complicated and are surrounded by many myths....it's like asking which is the best caliber to hunt deer with.
There are some very basics though:

A.) You want your prop to allow the engine to develop its horsepower and to stay within the recommended wide open throttle range (WOT) that the engine manufacturer suggest for the particular motor.
Most will give a WOT rpm range of between 5500-6000 rpm...with most optimum being 5800-6000 typically.
Pitch is how far the boat will travel in one complete revolution, considering 0% slip. So a 25" pitch prop in one complete revolution will theoretically move the boat forward 25". Think of the pitch of prop like gears on a manual transmission of a truck....the lower the pitch the more power and rpm's you will turn....the higher the pitch the more speed you can obtain…..but the limiting factor is the recommended WOT rpm range we just talked about above.
Every boat/motor combination has to have the correct pitch/diameter prop to allow it to operate at the recommended WOT rpm....so there are limitations.
To answer your question: Typically the lower pitch prop will give you a faster hole shot than a high pitch propeller...but then if you go to too low a pitch you will over rev the top recommended rpm at WOT....so you gotta find a prop that gives you a reasonable hole shot and keeps it within the recommended WOT rpm range.
4.) Your question on cupping blades on a prop....What does cupping do for the performance of the boat?
Excellent question!. It depends on where the "cup" is applied. If the cup is on the tips of the trailing edge of the blades it will create more bow lift....sometimes giving more speed or making the boat carry weight in the bow better. However, adding more cup will usually, not always, but usually lower your rpm a bit.
Cupping the long edge of the trailing edge of the prop will make it hold water better in turns and also will help lift the entire hull vertically instead of just bow lift.
Cupping the leading edge of a prop will help your hole shot quickness but will typically slow your top end speed down somewhat.
I could write 50 pages of info about props. On top of the above you have many different styles of props...I.E. Chopper props, Cleaver props, high rake props, low rake props, over the hub exhaust props, through hub exhaust props, Mod V-P props, two blade props, three blade props, four blade props even five blade props.
Each one being for a specific application and performance envelope.
Hope this answers your questions?
Boats are fun!