Allison xb2003/225 promax/sportmaster.

[gehol]

Worst water I've ever seen on norris, wake boats everywhere. I even saw a sailboat, first time ever.
I did get a few short runs and had a buddy make a video of one of them. In the video I'm doing 75 with a lot of positive trim but the boat is running level. I stopped by East Tennessee propeller yesterday to buy some lock washers and was talking to Joe about it. He said more setback (14") would also help to lift the bow. I'm trying to understand how this is, using the pad as a fulcrum, the more setback you have the more leverage the motor has to lift the bow?

You are absolutely correct in your thinking.

[catfish123]

For years, it has been a well established, well published, opinion/fact, that 14 inches of setback on an XB2003 was the best amount. Pretty obvious that adding more setback would lift the bow more. Just like a see-saw.

[gehol]

This is a cut and paste from a previous thread, and some of this info comes from Paul Nichols in a post a few years back on the Bullet forum.

There is a lot of mis understanding out there on jackplates. The fulcrum is NOT the pad. The fulcrum is the face of the jack plate where the motor is attached. Think of it like this; wrap one arm around the front of the motor cowling and push forward on the prop with the other and attempt to raise the front of the boat. This is what the motor is doing. The farther back you put that fulcrum the harder it is to pick up the front of the boat. As Don (Don Weed in original post) said moving the motor back makes the effective length of the boat longer. Pick up a sledge hammer by the very end of the handle. Hold it out parallel to the ground. Now choke up about 6 inches and repeat. Which position is easier to hold the hammer parallel to the ground?

So why do we move the motor back on high performance boats? Many of these boats run motors very high. I would expect the OP's boat may have the prop centerline 3-4 inches below the bottom of the boat. A boat like mine runs the centerline of the prop 1-3/8" ABOVE the pad, some even more. If you run the motor that high without a jackplate, the prop would be more than half way out of the water. Therefore we have to shove the motor back to where the water is higher relative to the bottom of the boat and is better water. At higher speeds even with my 12" setback my prop arc will have the top blade 1-2 inches out of the water. It is a constant trade off with set back verses lift. In my case I have enough horsepower to weight to move the boat fast enough to start generating lift. Most boats with a pad generate little lift below 60 MPH. You have to stuff air under the hull along with the motor torque to actually "fly" the hull.
Many think pushing the stern of the boat down is the same as lifting the front, it is not.

[big_o_tom]

So, ever since running 88.5 mph a few week's ago I have been pondering this in my mind...my boat is supposed to run best with a 12" jack plate, I have a 14" on it now. When I had a 9" plate with the 28 trophy at 1/4" below pad all it would do was 82 mph at 6200 rpm. Now with the 14" plate and the 28 trophy at 1/2" above pad it does 81/82 mph at 5500 rpm. And this is at well below neutral trim. So why is this?
Maybe the optimum plate isn't a 12", maybe it is 12" or more?
Why did the prop have more slip at 9" setback and 1/4" below pad than at 14" setback and 1/2" above pad?
Just a few things I've been thinking about...

I have to add something that I forgot about, lower unit went out last summer and I replaced it with a sport master 1.75, it had a regular lower with a nose cone and 1.87 gears. So that accounts for some of the difference, a couple hundred rpm anyway.

[big_o_tom]

Hoping for no more rain this week, hoping the water clears up so i can go bust my goal wide open!!! 90+ here i come!

[big_o_tom]

Haven't got to run the boat but a few times this year and I noticed something today that I wanted to put out on here. I went to the lake on the 3rd and met a buddy to go watch some fireworks. Before dark I took his wife for short ride around the island. I'm gonna guess she weighs about 130lbs, we were doing 83 in no time at all. I go back today for a bit and noticed that around 60-65 it seemed as though the front end was bouncing again only kind of hard, like going over some waves. It wasn't like chine walk at all but as soon as I wriggled the steering wheel back and forth a little it went away and I trimmed up a little and gained more speed and it wouldn't start doing it again until 60-65. Anyone got an idea what this is?

[big_o_tom]

This is a cut and paste from a previous thread, and some of this info comes from Paul Nichols in a post a few years back on the Bullet forum.

There is a lot of mis understanding out there on jackplates. The fulcrum is NOT the pad. The fulcrum is the face of the jack plate where the motor is attached. Think of it like this; wrap one arm around the front of the motor cowling and push forward on the prop with the other and attempt to raise the front of the boat. This is what the motor is doing. The farther back you put that fulcrum the harder it is to pick up the front of the boat. As Don (Don Weed in original post) said moving the motor back makes the effective length of the boat longer. Pick up a sledge hammer by the very end of the handle. Hold it out parallel to the ground. Now choke up about 6 inches and repeat. Which position is easier to hold the hammer parallel to the ground?

So why do we move the motor back on high performance boats? Many of these boats run motors very high. I would expect the OP's boat may have the prop centerline 3-4 inches below the bottom of the boat. A boat like mine runs the centerline of the prop 1-3/8" ABOVE the pad, some even more. If you run the motor that high without a jackplate, the prop would be more than half way out of the water. Therefore we have to shove the motor back to where the water is higher relative to the bottom of the boat and is better water. At higher speeds even with my 12" setback my prop arc will have the top blade 1-2 inches out of the water. It is a constant trade off with set back verses lift. In my case I have enough horsepower to weight to move the boat fast enough to start generating lift. Most boats with a pad generate little lift below 60 MPH. You have to stuff air under the hull along with the motor torque to actually "fly" the hull.
Many think pushing the stern of the boat down is the same as lifting the front, it is not.

My prop to pad was 1/4" below with a 9" plate, now it is 1/2" above with a 14"plate.

[big_o_tom]

Got to make a few runs today. First pass with a full tank of gas was 80.4 mph at 5750 rpm's. Last pass fuel tank almost empty was 88.3 mph at 5900 rpm's. A tenth of mile slower than this spring but I'm happy with that. 12 more gallons of gas and wait till this evening when the boats come off the water and I'm sure it's got a little mo speed!!

[FLYING BUTCHER]

My 2 cents. Ran them for years. 14" set back and try dropping the engine a 1/4" at a time. I think you will find higher top end by not running the engine so high. Higher isn't always faster. Have fun be safe

[big_o_tom]

I'm at 1/2" above now and I've thought about trying it at 1/4" above and 3/4" above just to see the difference. I had a go pro mounted on the rear to record the lower unit at speed. At 80 mph the bullet is about 2/3's under water, pretty cool to see the video.

[FLYING BUTCHER]

Be careful, if you get to high it will blow out, dona bat turn, and you will get wet!

[big_o_tom]

I'm glad you brought that up. Why is an allison in danger of a blow out / bat turn at less than 1" above pad when I've read of other boats (stroker) running 2"-3" above pad and doing just fine. Not that I'm wanting to go that high, just wondering why one can and one can't? Is it the lip on the allison pad?

[FLYING BUTCHER]

Weight and design of boat. Lip doesn't matter. I've run with and without. On my boats it needed the lip.

[K-DAWG]

I'm glad you brought that up. Why is an allison in danger of a blow out / bat turn at less than 1" above pad when I've read of other boats (stroker) running 2"-3" above pad and doing just fine. Not that I'm wanting to go that high, just wondering why one can and one can't? Is it the lip on the allison pad?

Its because of the lip. It forces water down behind the boat which in turn pushes the back up. By pushing water down at the back of the boat the motor doesn't need to be as high to get the same effect as Bullet and Strokers running 1.5 to 2" over the pad. Remove the lip and you can run high like Bullets and Strokers. Very sensitive subject amongst A boat owners. Some swear by it others think the boats run better with little to no lip. If you search it you will find a bunch of threads debating it. I do know that alot of guy's who have pad work done when running big power have alot of the lip removed. Pretty sure Darris does this also when he is working on drag boat setups for customers.

[big_o_tom]

I know its a touchy subject. I would like to drive a boat like mine with the same motor that had the lip removed so I could see the difference.

[xb03fs]

If it drove that much better with wife in boat, your weight distribution is way off.

Work on balancing the boat before you push to hard. A balanced Allison is a happy and more forgiving Allison…

My 2 cents. The difference between ok height and max height in a given boat is only a few mph, but an out of balance boat just isn’t fun to drive.

I typically run my boat 1/4”-1/2” below where I can run max mph and only give up a 1-3 mph for a given load but is much safer.

Work on weight movement.

[FLYING BUTCHER]

I can tell by your posts you are trying to "milk" everything out of your Allison. I didn't listen and doubt you will but let me just throw this out there. Your boat isn't anything different than the ones guys have posted on here. There is always someone out there that is a little faster. If you keep jacking things up and trying things guys have posted that haven't worked for them you are at the very least get wet if not hurt. Been there done that. Driving one that is "safe" and fun will someday be enough for you. I couldn't agree more with the above post. BUT you do what you are going to do.

[big_o_tom]

If it drove that much better with wife in boat, your weight distribution is way off.

Work on balancing the boat before you push to hard. A balanced Allison is a happy and more forgiving Allison…

My 2 cents. The difference between ok height and max height in a given boat is only a few mph, but an out of balance boat just isn’t fun to drive.

I typically run my boat 1/4”-1/2” below where I can run max mph and only give up a 1-3 mph for a given load but is much safer.

Work on weight movement.

Two batteries on the passenger side and one on the driver side. All tackle is on the passenger side and I keep two life jackets and a throw cushion on the driver side. I don't think weight distribution is off.

[xb03fs]

Starting battery cancels out battery on driver side.

Group 24 45 lbs group 27 60 lbs.
Fishing gear is likely 50 lbs or less…

Unless you only weight 100 lbs your out of balance.


Buy 75/100 bs of lead shot and put it in the passenger gunnel and try again….if you move the cranking battery to center in front of gas tank. 50-75 lbs will likely work well.

[big_o_tom]

When I bought the boat it was center steer. One battery on the driver side and two in front of the gas tank. You talk about hard to drive, especially after converting to side steer. So what should I do, move the starting battery from the factory spot to the passenger side compartment?