good vibrations, not so much

Boat: 08 Sanger V215 black scorpion 330 (110 hrs)

So I took the boat out today for the first time in a few months to run it, check fluid levels, perfect pass after servo replacement, and what not to ensure no surprises for our upcoming river trip. I noticed a small vibration while running at wakeboading speed (22 mph / 2500ish rpm). The vibration was running through the hull. My first thought would be the prop or shaft, but the vibration would go away at higher rpms (30 mph 3000ish rpms). Which made me think the motor might just be running a little rough at the lower rpms and it is resonating through the hull. The motor recently had an exhaust leak on the heads (gasket) that was fixed under warranty.

Now the problem, was this vibration always there and I am being sensitive because haven't had it out in a few months, or is something brewing that I need to tend to. the vibration wasn't so severe I was concerned and stopped running it, but I don't want an easy fix now turn into a more expensive fix later. Plus it is simply a little annoying. Any thoughts or suggestions.

Have the prop checked for balance is where I would start. It's common for a prop vibration at certain rpm's but not others. It's like a tire out of balance, at some speeds it will cancel out and you won't feel it but others you will. If you think it's the engine, run it in nuetral to the rpm it's vibrating at and see if the engine is smooth or not.

more than likely your prop. very typical systems of a bent/out of balance prop. also make sure the prop is seated on the prop shaft properly.

An unbalance vibration WILL NOT go away as your RPM increases, it will increase as well. The same goes for it not being seated properly. So I would say that it is not a balance/seating issue.

Without actually being in your boat to feel the vibration it is hard to diagnoise. More then likely it is a resonant frequency vibration that has always been there and that you are just now noticing.

It might be an exhaust vibration if that was worked on recently. A pipe or muffler could be touching on the hull and giving you a noise that is new because it was moved slightly with the work done. Try running the engine up to speed in neutral and see if your vibration shows up or changes. It might not even then because there is no load on the engine.

I have had prop vibrations act just like this. Slight vibration at mid rpm but gone at high rpm. The increase in water pressure at higher rpm on the prop blades as torque is being applied can cancel out the imbalance. Seen it.

I agree that vibes can occur at certain rpms and not other.

SO here is a song by the Natural Vibrations: http://www.youtube.com/watch?v=BGsEYJVZroM

had the same thing last year and it was the prop. Physically looking at it, I could hardly tell the prop had a ding. Put my spar prop on and the vibration went away. So I took the prop and had it fixed. No vibrations since.

If you dont have a spare, see if you can borrow one. It only take about 10 min to switch one out.

Thanks for all the input. I will try to swap out the prop with my spare and see if that fixes it. I will also try the rpms in neutral and will report back with my findings. Hopefully will get the boat out next Tuesday. Thanks again for the help.