#6: The Boat Is Vibrating
The faster you try to go, the worse the vibration is. You might also notice the engine racing, while the boat loses speed.
Something's likely gone wrong with the propeller. A nick or gouged blade can create imbalance and vibration; a towrope or fishing line can snarl the shaft; a direct hit on an object could remove or misshape enough metal to make the prop ineffective.
Sometimes a seemingly good prop might have enough unseen distortion or damage to cause cavitation and vibration. Short of changing to a spare propeller - which isn't always possible or advisable when on the water - your best option is to slow down and concentrate on getting to shore.
If fishing line - especially monofilament - has worked its way into the propeller hub, you might have to trim up the motor until you can remove the propeller and clean it out. Most outboards and I/Os can stand a bit of mono, but if there's enough to cause a noticeable decrease in performance, you shouldn't ignore the problem, as it could lead to permanent damage.
With outboards, the rubber bushing inside the propeller hub can begin to slip and fail, causing a loss of power. Again, you might need to idle home.
Consider carrying a spare propeller, along with the necessary tools to make the swap. Practice changing propellers so there are no surprises, if you have to do it away from home.
Gloves to protect your hands from propeller blades and a brand-specific propeller wrench.
We hope this List assisted you in your ability to remain calm in the face of possible "on the water" problems, helping to insure many a successful boating adventure.