I need way more information.  What engine do you have ?  What year is that engine ?  Was the engine balanced ? 

A common problem with Panther pumps is the shafts are weak.  In turn you could have a bent shaft which will cause a major vibration, but it probably would not go away at the given rpms that you are talking about.  Another problem is this, you could have a total imbalanced impeller; i.e. chip, crack, dents, chunk of wood.  If your u-joint is going bad, it will vibrate, An easy fix.
If the driveline angle is beyond 4 degrees it could cause vibration also. 

Jim

I'm gonna go out on a limb and say that it shouldn't do that!
Replace the u-joints and check to see if the shaft has play in it. Who did the work on the floors and stringers?

ok more info. it is a 21 foot crusader jet boat. the motor is a 454 bored 20 over mid size marine cam some head work and it was pro built by a engine shop in town. the year may not be exact but the boat is a 1980 so i am guessing the motor is from around that period. as far as the engine being balanced.i dont think it was i started it for the first time once it was in the boat. Thank you for all your help. i guess i am going to replace the u joint first since that seems to be the easiest step. once i get it off i am going to run the motor without the jet drive connected to see if maybe the motor is causing this but i dont think so. How do i check the impeller of the jet drive? also the gear oil in the jet drive looks a little milky like there is a bit of water in there could this cause a vibration? and how do you get that oil out of there. i cant find a drain plug anywhere.

thanks for all your help

tony

oh yeah....welcome to the site tony 

I merged the 2 threads you created so everyone is on the same page. 

... You can post everything we talk about. Except what I say about Brad...

Now that is freakin funny! LMFAO   

i guess i am going to replace the u joint first since

Tony,
Just disconnect the driveline and run the motor before you go out and spend money on new parts.  Running the engine with the pump disconnected will tell you right away if it's the pump or not.
Unfortunately, I've read a lot of misinformation given about the Panther pumps in here already......ughhh.
Unlike the Berks, Doms, AT's and others, Panthers come stock with a stainless steel impeller.  It's not real easy to chip, nick or gouge one to cause a vibration.  Engine alignment needs to be within 1? to 3? of the centerline of the pump shaft, if it's off you run a chance of a vibration.  You can also get a vibration from something wedged in the impeller, ie: a piece of wood, a plastic bag, a rock, etc.
As far as the shaft, yes, it can be the weak point with 550 hp or above but bending or breaking one with mildly built engine is very unlikely under normal conditions.
You said that the pump was supposedly rebuilt before you got the boat, there's a real good chance whoever did it put the water seal in backwards.  If that's the case, it's the reason why you have water oil the oil reservoir.  There's also a chance they put the du bushing in wrong or when they removed the old one, they damaged the housing where it sits.
I've seen a few where it appears the person used a saw to cut the bushing out.  They went too far and put a nice little cut in the aluminum.  The worst is when someone decides to use a big hammer to remove the shaft, lots of things go wrong when that happens.
Oh yea, I've been rebuilding these things for quite a few years now.

wow thanks for all the info. i dont think it is the motor itself but as i said i have only ran the motor with it connected to the drive. I am giong to remove the drive from the motor and see how it sounds. if the sound is not there what is the best way to determine between the factors that are left. ie the pump, the u joint, or alignment.
And yes my motor is pretty mild. a smal overbore an intake  and a cam. that is about it. this is not a race boat.lol.

i can not get back to the boat until next weekend i have a wedding this weekend and the boat is in blythe at our trailer. i really appreciate all the help so far guys. this is my first boat and i wish i could have came here first i would have looked for something different.

oh and due to that wedding i can not make the parker race. Hopefully i can figure out this hull vibration without bothering some of you smart guys for help

I looked at another boat last night that had a Panther pump in it. It also had homemade looking engine mounts in it just like all of the other boats I've seen with a Panther pump, which is less than a handfull of boats.     Freakin' thing had a AMC small block engine with that Panther pump.   

That's an AMC 360, 1 of the Panther packages that was pretty popular back then....the least expensive one, from what I understand.  They really aren't bad unless someone is looking to go fast    They did get some pretty darn good gas mileage and would push most 18' boats to 60ish.
I think that boat in the the "Go Wild" Panther movie is a 360.

you guys are very helpfull. i am kind of leaning toward this being an alignment issue. i redid the floor and trusses in this boat and i had never owned a boat before. when we put the motor in we measured the best we could but we basicly just eyeballed it. like i said my first boat..haha should have taken my time but i needed it for easter weekend. I will inspect all these parts as you have stated and post the results when i have finished my troubleshooting. i hope it ends up being an easy fix.

but i dobt it... it never is

later
 tony

i dont know how fast they are supposed to go. i have a 20ft boat and it will only run about 44 at around 4500 rpm. is that normal. also i have not really tuned the carb yet the last trip was just to break in the cam and let the motor wear itself in.

that is the most helpful pic yet. and yes i remounted the motor mounts you see in the pic. i dont think i am too far off but i might be. now that i see what you are talking about i will have a better clue on where to measure.  i am hoping it to be an easy fix. because where those motor mounts are it would be easier to modify the motor mount than it would be to change its location on the truss.

you are one helpfull guy to know. i will be going to blythe next weekend to try and solve this problem. are any of you going to be down there that weekend??

well i will be down there at mcintire park. should get there late on friday night. i am going to wake up and test and tune the boat all day. try the easy things first and see where we are at. and if i get it fixed on sat it is fun in the sun on sunday. if the problem still exists then some more wrenching on sunday.