Side to side rocking?

[K-DAWG XB 2003]

What is it exactly that cause the boats to rock side to side when you come off plane to fast? I know when I was first learning to drive it with the 2.5 liter I ran into this problem a lot. After learning to drive it I never had this problem. Fast fwd to the 3.0 I now have on the tail. I am again running into this problem with the 3.0. In the places I use to run I knew how long it would take me to slow down. The 3.0 doesn't come off plane like the 2.5 did. It wants to rock side to side coming off plane in the same spot I would normally start coming off plane to stop or slow down with the 2.5 liter. Apparently, I need to start slowing down a lot sooner than I normally would have with the 2.5 liter. So, what exactly cause the side to side rocking?

 

[xb03fs]

I wonder it that is the non-ratcheting gearcase of the 3 liters, I have no idea. Just a guess. There is a guy in Florida that says he can machine a part of the gears to make them ratchet????????

 

[GotMyAlly]

Something besides chine walking you're talking about here, I presume? I don't think i've experienced that with the 3.0, but mines on a bigger boat obviously. Does it do it with every prop?

 

[RedAllison]

Several "suspects" pop into mind. 100 extra # mainly up above the mid-section, that makes for quite a bit more leverage. What prop? If you are utilizing the torque of your big block then you likely have a bigger barrel, larger diameter prop like a X-OB, Bravo etc.. Those would hold the stern up & allow such motion, especially exaggerating the above "100# heavier comment". Our 21s have a quarter ton more hull weight, ALOT wider front to back, carry more of everything & in general just have more "arse" to hang onto than the 03 so we don't see this as perhaps you are? This is why I wonder if indeed the "tail is waggin the dog"???

 

[chad202]

The boat coming down and hitting the hook on one tri-step before the other and pushing the boat over. Then that side hits and pushes you back over. JMO. Same reason why they harder to drive 75-80mph.

 

[scj]

Lee Sanderson recommends trimming down before you back out of the throttle on the 2003's. I used that method without incident when I ran my 03 last year but in the 21'er, he said to retrain myself to lower the jackplate in lieu of the trim lever.
You don't want to slam the front end down as you'll lose contact with the prop but trimming down 10 to 15 percent before you crack the throttle is very noticeable and keeps the rocking at a minimum.

 

[K-DAWG XB 2003]

It done the same thing with the 2.5 on the tail until I learned how to slow down. This isn't something new I was just wondering what causes it. Just having to relearn to drive the boat.

 

[K-DAWG XB 2003]

Just having to relearn to drive the boat. I don't get to go out an run it every weekend. I get a chance maybe once every 2 weeks if I am lucky. Anyone who tells you it didn't change the boat that much going from a 2.5 to a 3.0 liter motor is either superman or the best Allison set up on the planet. The boat hasn't really scared me and made me think I made the wrong choice. I am just having to learn to drive it all over. Thought this was the place to ask these kinds of questions and get help in understanding what is causing it to act a certain way. Am I mistaken?

 

[GotMyAlly]

Refresh my memory.....did you come in on the jackplate when you mounted the 3.0L?

 

[K-DAWG XB 2003]

Yea, I put a 5.5 inch plate on it. I just need to get out a get more seat time. This is the exact same thing I went thru when I first got back in 2008. Just gonna have to start slowing down sooner. Apparently I need more room to slow down than before. It doesn't slow and come off the pad as fast as it did with the 2.5. Because I end up further along still carrying speed that causes me to get out of the gas a little harder because Im slowing down for a curve running right at the bank with now where else to go. The next thing I know I am rocking side to side. That's my take I was just wonder the dynamics that went into it and I would have a better understanding of why's and how's. Maybe help me keep from doing it.

 

[whipper]

My gS does that some times also until im below 65. i always thought because Im still 60+ mph as I come off the gas and start to trim down im still on the pad regardless at those speeds. I just thought that with the prop parachuting the hull down and the trim creating more drag it was just harder to ballance for a bit some times if i come off rather quickly? Sorta like chine walk on the way down since im still on the pad? If that makes scents.

 

[whipper]

Oh one more thing i think i noticed. it seems to be worse the higher the jack on that run also. If im at 1/2 or 1/4 below its not even noticeable and or with smaller pitched props. But if im at even to above the pad and come off as i come down in speed there is more of a tendency to have to keep steering until she settles down {off} the pad. ballance also seems to effect this. Or off set.

 

[chad202]

The reason I feel I know this is because I sanded the hooks on my tri-steps off on my 03 and my boat didn't do that anymore. Nor did it walk 75-80 like they all do.

 

[whipper]

The reason I feel I know this is because I sanded the hooks on my tri-steps off on my 03 and my boat didn't do that anymore. Nor did it walk 75-80 like they all do.

Chad are the tristeps the the really curved end of the strake ones and guessing third ones up without going to look?

 

[K-DAWG XB 2003]

So out of all the people who are here on Allison owners this has only happened to 3 people?

 

[xb03fs]

I don't know man. You have a unique setup. Maybe if you went from 14" to 5 and as you say it stays on the of longer, maybe try a set of 2" or 1" spacers and see if a little more setback helps. Or it could be the non ratcheting of the three liter case

 

[K-DAWG XB 2003]

I don't know man. You have a unique setup. Maybe if you went from 14" to 5 and as you say it stays on the of longer, maybe try a set of 2" or 1" spacers and see if a little more setback helps. Or it could be the non ratcheting of the three liter case

It done the same thing with the 200 2.5 liter on the back with 13.5 inches of set back. Nothing unique about that.

 

[chad202]

It's the part that sits on the vertical bunks all the way in the rear. They have a hook just like the pad but WAY bigger.