Propulsion shaft alignment

And?

In other words, what are the design tolerances supposed to be?

Hello Guest,

I had a few minutes to read your Posted Topic.

I have decoded what you are asking, I think.

You do not give your location, Ship size, engine HP, RPM, bearing type, or shaft and flange size.

So...it is much of an educated guess here.....

The mating flanges should be perfectly parallel, in all directions = equidistant all around.

Tolerances for bolting up, are normally within .005 inch, or 0.1 millimetre.

Otherwise extra lengthwise (= longitudinal = in line with the shaft), strain is put on the bearings.

Your Gearbox and shaft are mis-aligned.---- (Top and bottom)

For bearing long life, both the mating (=joining) flanges need to be perfectly parallel.

If you accept what you presently have, and allow the shipyard to just bolt up those flanges, you are going to ruin those expensive new bearings.

Ask the shipyard to properly align the motor - gearbox, and all shafts, so that all mating/joining flanges are equal distance all around.

The flanges MUST be perfectly parallel, if they are to be bolted together without damaging the bearings.

Apart from that, misaligned couplings are going to give the ship large vibrations, which may damage the ship's welding joints, undo structural bolts and nuts, also will annoy the Captain, crew and passengers.

There is also another problem from misaligned shafts: Leaking shaft seal, which will flood your bilges, and sink your ship.

Advise here further .....

Am I completely off base, I would have thought that such tolerances should be allowable, they seem fairly small.....does a universal coupling of some sort not handle that amount......?....but others of you feel that it must be perfect....

I am going to keep an eye and see what you all come up with.....

Does your hull flex?? Alignment should be checked when afloat.

First, I agree with JohnDG (#1)... And?

Second, I also agree with Andy (#4) that a coupler should be able to handle a certain tolerance of misalignment.

Now, you say the shipyard is DOING the alignment. Are they telling you they cannot align it or that you need to pay big $$$ for them to align it, and you are having second thoughts?

The .1 mm most certainly would be included in the tolerance of a coupler system. The .5 mm I'm not so sure. Looks like the manufacturing specs should give you a clue on this.

-John

As already posted there are a number of items that need to be stated.

When I was working in the ship yard, When they installed the struts they where roughed in prior, and after they where installed, they mounted a portable line lathe for the machining for the drives for the screws.

Are you asking what you should do, to this misalignment, or if it will pass?

First of all what type of couplings are fitted on your drive line assembly, e.g. rigid or flexible?

Is the gearbox close coupled or remote mounted?

Does the prime mover have inspection doors? You then may check final alignment by taking a crankshaft deflection test. (This is rule of thumb and dependent on engine/gearbox manufacturers recommendations).

What are the dimensions of your shafting and where are the two pedestal bearings placed, particularly the distances from the couplings.

What are your stern tube bearing details, e.g. inner and outer bearings?

Is the stern tube conventionally packed or is it a PSS type seal?

If you have a conventionally packed stern tube what type of packing are you using and what is the propeller shaft material.

If you would care to answer the above questions I will try to assist you to carry out your alignment correctly.

Before final alignment is carried out ensure that:-

1. The vessel has been in the water for a minimum of 24 hours.

2. Ensure that all fuel, water and ballast tanks are between half and three

quarters full, this will equate to a normal vessel loading whilst underway.

3. All permanent ballast in place.

4. All major machinery...over 450kg....is in place, or simulated equivalent masses

appropriately placed.

For the best maintenance free coupling existing, contact Coupling Corporation of America, at 1-800-394-3466. They are in Pennsylvania and have a very good product.

David, Guest