engine and shaft alignment

Thats a tough challenge without looking at it .

Vibration could come from anywhere even an unbalanced shaft but the assumption is the replacements should have been ready to run.

Alignment in a boat maybe be difficult the only way that comes to mind is a string it is commonly used for other applications so It may apply .

Check out any carrier bearings and try running the motor separately to isolate the vibration you could have bent the crankshaft or run with the props removed .

I hope thats helpful

Can the shaft and the prop be separated and re bolted in a different relative position? This might be worth a try if it is a balance issue. Or run it with out the prop and see if you still get the resonance?

Step by step procedure is explained in our website: www.yesyen.com > Downloads > free downloads > graphAline.

Yes there is a step by step procedure. But not something for the inexperienced owner to attempt.

That must have been some deadhead and some impact! If you wiped out all your underwater running gear, chances are the struts were also affected. Possibly even shifted out of alignment

The website referenced by one poster doesn't really address the boat hull issue. FRP is flexible. You can only check alignment when boat is on the water and after it has floated for a few days to relieve stresses and distortions created while blocked up in dry dock.

If your vibration only shows up above 2600 RPM chances are it's in your prop. Even new props have been found to have imperfections. There is a process called "Prop Scan" which uses very precise dial indicators and an indexing table to accurately profile and digitize every blade and compare the blade against a computer model and then compare each blade against the others. The Prop Scan process will indicate exactly where and by how much the prop shape has to be changed. Usually this is done by forcing the blade into true alignment. In rare cases cast props which have not been carefully machined will have one blade slightly different than the others.

The process of aligning the engine and shaft coupling faces makes an assumption that the stuffing box, and the strut and cutless bearing are all in perfect alignment and completely concentric. Not always true.

I have seen instances where the strut was bent and the FRP mounting surfaces damaged. The repair glass work meant the mounting holes had to be redrilled . If these holes are ever so slightly out of position, the shaft may be forced into a curve. It doesn't take many thousands of an inch to cause vibration. We once had a boat (at a dealership I worked for)where we could not get the alignmnt right. The factory mechanics said it was the best they could do. Our crew chief said it wasn't good enough.

Sure enough the client took delivery of the new boat from the factory and the starboard engine shattered after less than two hours running time at full power.

As the selling dealer we had to get the shaft log repositioned to make the alignment correct. After that the boat operated for several years with no further problems.

In new builds it is now common to use very taut piano wire and laser alignment tools to verify that struts, shaftlogs and engine beds align perfectly before the running gear is installed.

This is not something for a DIY boat owner to attempt. If the yard in which the boat is dry docked now is not experienced in doing this kind of alignment get a specialist crew in to do it or take the boat to a yard with experience in doing this work.

Vibration wil ruin shaft seals, cause premature failure of equipment like your transmission bearings and generally be a source of ongoing aggrivation.

The first thing I would do, is use a simple deflector clock securely fastened to a point near the shaft or shafts, and check for deflection, in the area between the gearbox and gland seal box, if you find this acceptable, ie within +/- 0.0025" then do the same with the outside, between the hull bearing or stays or whatever you have there, if again you find this acceptable, dismantle the drive coupling, having first made a suitable support for the shaft in the way of a `vee` block just to support the weight of the shaft, if the amount of overhang from the stern tube is not great, it may be possible to do without this, then do the deflection check again, if you are still within limits, then I would run up the engine if this is possible in the dry dock, and check the engine at various speeds using a vibration monitor, Something else has come to mind, if you had to replace both props. have you checked the taper on both shafts for possible `windmilling`It's my bet that most damage would have been done to this area, considering the amount of damage to the props. Hope you find this helpful! I have worked all my life on or near small boats, and vessels up to 120ft. istalling engines up to 2,500 hp, down to a tiddler at 2hp, I always found it easier to go for the simple things first, one problem we did have with an 8 cyl. Rolls Royce Diesel was similar to your prob. it turned out to be a driven coupling which been machine out of concetricity, giving the impression the shaft was bent!

After you try some simple things, look up a vibration consultant in your area with marine experience. Alignment and vibration are complex. I teach a class on both subjects and it is far too much to 'teach' via CR-4. You may have a lot more damage to transmission, coupling, engines, engine mounts . . . . . not just alignment.

I made a blunder when I read your thread, I didn't realise you had also replaced the shafts as well as the props. on the question of your vibration, when you had the shafts replaced, the engineer presumably, checked the alignment correctly to the gearbox couplings, with an ordinary replacement one would not expect there to be hardly any difference in the alignment, however there is a check you can do on the outside gear such as the "p" brackets or stays, Remove the shafts, and make a plug for the inboard gland seal, or stern gland, drill a hole to suit whatever piano wire you can obtain, make up a strong back from the stern of the vessel, with a suitable hole to suit, pass wire from inside, and tension, this can be done simply by drilling a bolt lengthwise, with the nut welded to the strong back, then screw bolt to tension the wire, when the wire registers correctly on the outside stern gland, check this by means of spring loaded inside calipers, (these can be measured by a micrometer if required,) then check the position of the outside stays, again by the same method, having ascertained that everything is within tolerance, I would then replace the shafts, and carry out a similar check as my previous thread on the inside, using a deflector gauge, also run up the engines with the shafts uncoupled, and check for engine vibration with a monitor, in the different speed ranges especially in the speed band that you are experiencing the problem, if nothing is found, then there remains for you to put the boat in the water again, and recheck the alignment with the boat afloat, if OK, then do a series of sea trials and ascertain which engine is giving you the vibration, go for the simple things first! Good luck.

Have you run it at that speed dry before and was it smooth? Were the replacment props/shafts/bearing etc. identical to the original equipment?