Handling question

[CCfishing]

2017 Mercury Pro XS 150
Serial #2B361294
2017 Nitro Z18

Hey guys, I have about 230 hours on it. For the first time ever yesterday, I noticed my boat kick out or slide to the right a little only when I trim down. The first time it happened yesterday I was hours into my fishing day, and it kind of scared me when it happened. I tried to make it happen again to see if it was something consistent. I did happen a couple more times while trimming down and driving mid speed, but not as intense. I have an adjustable jackplate that I have never had performance issues out of. Any idea what could be going on?

I appreciate your help.

[EuropeanAM]

Check steering fasteners, bushings, hardware, and adjustment (as well as verify fluid level and no air in system).

Check ENGINE and JACKPLATE fasteners.

Check SKEG for any signs of damage (prop and hub also).

[revlimiter]

Have you changed anything? Hydraulic plate? Sounds like the prop biting when it comes back in the water. Any damage to prop recently?

[CCfishing]

Thanks guys, I'll check on those things...

I have not changed or touched anything since I've owned the boat (Fall 2016)....and always ran great
-Manual Jackplate

I did hit a small floating piece of wood recently, but definitely no damage to the prop, hub, or skeg.

[JOE54]

were you by chance running in water with a current , I have had some move around a lil more when in river with more than normal current

[djb750]

My Ranger did this intermittently too. I typically don't run balls-out, but cruise around 4600 RPMs, which is around 50MPH or so. When mine did this, it felt like the ass-end shimmied real quick. Definitely a "whoa what was that?" kinda feeling. So I got to working on and verifying the setup for my boat, and for me this issue has never come back. The first things I did were as mentioned above with bolts being properly torqued, etc, and your hydraulic steering filled and bled properly.
Here's what I learned:

• Prop to Pad. Since I didn't need to have the ignition ON to measure and adjust prop to pad height, early on I didn't take into account where the needle was on the trim gauge when the lower unit was parallel to the pad. I used a carpenter's level on the pad and lower unit, and once they were level and parallel, I took the measurement and adjusted. It sounds kinda dumb, and I guess it was, but at some point I was like "well, let's just see what the trim gauge is showing..." And I was kinda dismayed that I wasn't trimming it out far enough based on knowing where the trim gauge was went it "felt right".
• A lot of guys can, and say to, go by feel as to how much to trim out on plane. In my case, it felt good, It sounded good, the RPMs went up as I trimmed out. But it needed a bit more is all. It wasn't much, but it was enough that it made a huge difference in handling (and top speed), knowing where the lower unit was when parallel with the pad or slightly beyond.
• I also noticed a spot of cavitation burn on my skeg and I think a bubble was releasing into the prop when I felt this shimmy.
• My transducer is mounted just off center, to starboard, inside my jackplate I changed the mount and raised it a bit. If the water flow is disrupted in that area, it can do weird things. All I can say is there's a whole science behind water flow over a foil, adding a little turbulence to otherwise laminar flow, and all that.

So I don't know what the setup is for your boat, but the guys in the Nitro forum should be able to help with guidelines for your boat, and here for your engine.
Hope you get it solved. I really think it's just something with your setup.

[OldTimer57]

This is not that uncommon, particularly the last two months on the Coosa. 60K cubic feet per second (and up) over the spillway, 30K through the turbines, produces serious current. Odd things on the bottom (big rock, hump, etc) can greatly disturb the water and if the water moves in weird ways, your boat is going to move in weird ways.

Just be sure it is not a steering problem, a motor mounting problem (motor to jack plate, jack plate to transom) and not a motor mount issue. Ought not be able to move the motor much from side to side. ¼" and beyond indicates trouble in river city.