Future Allison boats

[GPI Racing]

Lars,

My prefered "size" of this lip is about .040". I even taper it to nothing in the middle. This has given us the best overall performance with the boat/engine you have. The reason for the outside having more than the center can be traced to the old tunnel boat days. We used to do the same thing on the tunnels. (put a little lip on the outside) The water coming down the pad doesn't go directly straight back. Some is diverted to the side from the boat displacing it weight. This is much like the shockwave on a airplane. (the triangle shaped "wave" you see in the airplane photos) We've always tried to use this "sideways" energy to add some lift to the rear of the hull. The center can do the same but the drag penalty is much higher. The "shockwave" is there and you can't get rid of it, so might as well use some of it.

Froggy...anything you can add? (he's loaded with aerospace info AND has lots of Allisons!)

Randy

 

[froggy]

Lars,

We understand yoour reluctance to get out the file/sanding block. Try this: take the lip of your pad down to .060" all the way across. This is the engineering design height of the original 2003 lip. Run your boat at this height and see if you are happy. This lip size seems to work pretty well with 14" offset and a 280. Your hull should keep the nose flying here.

If you want more, you can always "flat top" the center of the pad next.

froggy

 

[cj707]

No reluctance here! I have no problem taking it down to nothing! I'm running 12" setback and plan to try less. The boat has much better balance just going in 2.5" But I think, like you guys are saying: Less setback-less lip. So...If I go to 8" of setback and 0-.040" lip. Will I still be able to carry a load? I'd love to give it a shot. Like anyone who has run the 03 100+ The nose drops and the stern gets too much lift. So the only down side I could see to sanding the lip down is weight carrying ability.

Great thread!

Lars

 

[John Richied]

Lars good to see you posting so much ....How is the GPI 280 running?

With the lip modifications and I have done NONE I think the only downside is if you take an XB-2003 or XB-2002 and shave the lip then go down in power to lets say a stock 225, then you are going to hurt the performance.

With more horsepower if it handles better and runs flatter you are going to run FASTER… let her EAT!

The weight, fishing load won’t be much of a factor if the propshaft horsepower is there to push it… set up accordingly and balanced of coarse.

 

[chad202]

:? Mine was blueprinted at the factory and my lip was reduced in the middle and tapers off to nothing on the sides..... :?: Before getting into the upper nineties and triple digits, should I lower my motor to even or maybe even below the pad. I'm currently at 1/4" above and so far, the boat handles fine at 95mph. I just don't want to do no spinning out at high speeds.

 

[fishnfireman]

Chad you say yours was done by Allison ?
If I am reading this right -it is the exact oppisite of what Randy described.
Is the difference again because of the horsepower. :?:
Where as Darris is always trying to do more with less.

Or has Randy just hit on something better :idea:

 

[chad202]

You are reading exactly right. Mine was done at the factory when the boat had a 225X on it. The last 1" on each side doesn't have a lip and from the middle, the lip gradually tappers off till it gets to an 1" away from the side, then nothing. :?:

 

[Casey G]

Mine was blueprinted at the factory and my lip was reduced in the middle and tapers off to nothing on the sides

that's the same as the lip on my 01 XR Drag

 

[GPI Racing]

I've tried that too. While it works just fine, here are two things you will notice one way compared to the other. With the lip high in the middle and tapered toward the outside, the boat is more squirrley and the water flow to the prop is kicked down or compressed. This will alter your effective propshaft height slightly. The big difference is the squirrleyness. You have to test this back to back to really tell but it's there. I'm all for a better handling boat. Lots of guys here will say this way is faster or that way is, but I feel if you can drive the boat better because it is stable, you'll always be quicker. Yes,there are some great Ally drivers out there, but for the rest of the world if it drives nicer the guy will be faster.

Randy

 

[Blueally XB21]

Randy,
Have you or anyone you know experimented with pad mods on the newer XB21 hulls? What is your opinion on the XB21 hulls and pad mods? Does this pad mod make the hull more sensitive to weight? Is a pad mod something that helps all around hanlding and performance with larger motors (i.e. higher speeds, 100+)?

 

[froggy]

Chad,

Your pad, and lip are exactly as the factory delivers them, except yours should be "right on" the engfineering spec. The question is what spec was used---.060" or .090"---Allison has used both. My boat, from the factory, was way out of spec at .150", talk about lifting the transom (manifests itself as dropping the bow)!

Lars, I have my boat set at 8" of offset now, but I haven't tested since it became cold. I was at 5.5" of offset and still had lift, but had to trim a little more than I liked to get the lift so I went to 8" of offset instead of shaving my pad any more to get the lift. If this works, I will leave the offset alone and optimize my pad.

froggy

 

[msethsmile]

GPI

Randy,
Thank you so much for the compliment. I stood on the shoulders of giants...

 

[cj707]

Froggy, is your lip at .060" ? How is the best way to measure?

Thanks,
Lars

 

[chad202]

Froggy, don't know haven't measured that yet. It was blueprinted in 2004 I believe.

 

[froggy]

Chad & Lars,

There are several, acceptable, ways to measure lip and some start with leveling the pad using the tongue jack. Make sure the surface, under the boat is level. Some folks level an "I" beam under the boat. Now use a dial indicator on a base and set it on the "I" beam about 1 foot forward of the lip and take a measurement. Now move the dial indicator under the pad lip and take a measurement. Subtract the two and you have the lip height. After doing this a few times we usually find an easier method and that method involves using shims. Find a 1' - 2' long bubble level and some scrap aluminum or thin cardboard, etc.. With the pad level, put the bubble level on the pad lip and put cardboard shims about 1 foot forward of the pad lip. Keep adding shims until the bubble is level. Remove the shims and measure their thickness with a dial caliper---voila, you have lip height.

I use shims and a straight edge to cut the lip also.

Lars, I had my pad lip at .060" when I was at 14.5" of offset. The boat held the nose up at speed and ran well. I just didn't like the rough water handling the water on the back deck and the nose high attitude when fishing and idling. Now my pad lip is at .045" and I'm hoping that it will work here with 8" of offset. .060" was just fine at 9" of offset, but I want to be able to lift with some negative trim so I'll get transom lift from the gearcase.

I hope this helps.

froggy

 

[fishnfireman]

Could you use a feeler gauge :?:

 

[cj707]

Hey John...

The motor is awesome. It's been soooo long since I've had a motor that ran worth a sh*t. Now I'm gonna try and screw everything up by sanding on the pad and throwing all my set back away.

Lars

 

[John Richied]

Lars, I think your getting more into high-performance then fishin… hehehe

Okay, a high-performance fisherman…

 

[froggy]

Fireman,

Yes, you can use a feeler gauge to check the lip, along with a bubble level.

froggy

 

[Blue Gray in PA]

Would I be correct in saying that a lower horsepower motor can use more setback than a high-HP one - all other things being equal? If I stay with my 150HP and go to 12" setback from the current six, would I get more bow lift at speeds? And more water over the back on quick stops due to the weight hanging further back?