Help my boat in vibrating

[A&EPerico]

Hi Guys. I took my boat out for the first time this season today. It was running great all morning. On our way back to the dock area I was going about 20-25 MPH for about 5 mints, and out of know where I felt a large and violent vibration. I immediately put the boat in neutral and opened the engine compartment. Everything looked normal engine mounts in place nothing unusual. So I put the boat back into forward motion and it appeared to be ok, but 30 seconds later the vibration came back. Any ideas as to what this could be? Once out of the water I inspected the drive shaft and prop, they appeared to be ok to me. The boat only has about 30hrs on her. It is a 2005 22I. Any help would be great thanks guys!

[R&T Babich]

.... It was running great all morning. On our way back to the dock area I was going about 20-25 MPH for about 5 mints, and out of know where I felt a large and violent vibration ....

My first thought was maybe a bad plug wire or plug, because our boat had a cracked plug (I think from the factory), but it actually ran ok. It had a fuel rich smell to the exhaust and now has a lot better feel to the power.
Second thought was maybe a cracked or faulty distributor cap firing a cylinder at a really bad time, like in the middle of an upstroke.
Did you check the driveline connections between the engine and the prop shaft. Maybe the shaft coupling bolts are a little loose.

Does the vibration feel like it is the engine vibrating around or is it in the hull of the boat which would tend to be driveline related.
Did the vibration come back at a certain speed?

[samw]

My first thought was maybe a bad plug wire or plug, because our boat had a cracked plug (I think from the factory), but it actually ran ok. It had a fuel rich smell to the exhaust and now has a lot better feel to the power.
Second thought was maybe a cracked or faulty distributor cap firing a cylinder at a really bad time, like in the middle of an upstroke.
Did you check the driveline connections between the engine and the prop shaft. Maybe the shaft coupling bolts are a little loose.

Does the vibration feel like it is the engine vibrating around or is it in the hull of the boat which would tend to be driveline related.
Did the vibration come back at a certain speed?

Also along with R&T, run the engine rpm With Out engaging the trans. See if the vibration or any other noise comes apparent. If NO then you know it is something regarding the trans Vdrive. I hope that helps a bit.

[A&EPerico]

Thank you very much. I am going to take a close look; at everything you mentioned hopefully I will be able to figure this out. Thanks again.

[A&EPerico]

The vibration felt like it came from the Hull. It started to vibrate at about 20 MPH. I was freaking out!

[A&EPerico]

Thanks guys for all of your input. But, I gave up I made an appointment to have the boat looked at. I can’t figure it out.