Marine Shaft Alignment

If the packing gland near the propeller is tight (centered) and the bearing with .020 clearance is near the engine, the shaft will need to be lifted .010 for correct alignment when the flange faces are parallel.

Hi Mathew. aligment shafts vertically or horizontally requires a lot of visualization. I don´t know if this site has provision for presenting drawings or photos ( wich could be a good idea).Anyways there are many ways to present the readings and outcome of the final aligment but at the end the shaft is going to be in only one physical place. I mean, you can get confused or misunderstand your own readings (I have been doing this for 28 years in both thermal and hydarulic power plants). In adition taking aligment readings at different times of the day on the same spot may give you diferences that you may think comes from your adjusments. You have to consider that the housings and bases where your equipment is sitting will move, vibrate, expand and contract. You can send me photos or drawings to my address so we can take a look at it and give you an advise if necesary. For sure we will learn of this at the same time. llizarraga@pancanal.com

I think, from the info recieved, that the suprvisor is right. It was said that the propeller was not on the shaft, so all of the static forces had not yet been applied. The shaft sags under it's own wieght. Add the weight of the prop and a fulcrum (the cutlass bearing)at one end to the once sagging shaft and you have found that the calculated alignment was correct. Experience will teach you a lot, but by listening you can learn it painlessly. And I hope you commended your supervisor on his fine skill. Is that Brisbane as in Aussie Town?

I just removed 1 1/2 inch shaft for inspection and to replace the bearing in the strut. How should I check the alignment between the center of the strut and the center of the transmission coupling? I've heard of "target wire" but not sure how this process works.

you said clearance in the packing gland/stern bearing - youmust center the shaft in this area not let it rest on the bottom - it alloes error - also account for sag.

Matthew,

There have been different schools of thought presented to me on marine propeller shaft alignment over the years and I am sure you have seen as many crazy things as I have. The theory your supervisor seems comfortable with is that the difference in the gear output coupling and the shaft input coupling half is there because you had squared it when doing such a fine job of aligning it. In other words, when you made the coupling "square" with the length of the shaft by moving the engine to it, the shaft then being stiff and difficult to bend "flew" to the center of the bearing nearest the gear output flange much as it will do anyway in motion. Rest assured it is still under the influence of gravity and the end of the shaft nearest the propeller is lying in the bottom of the that bearing in the strut. You have simply centered it in the bearing closest to the gear output shaft.

For instance, if you had used a laser or wire alignment fixture to align the engine making the entire support assembly system for the shaft, and the gear output coupling theoretically straight and square, you would have arrived at the same point with the shaft coupling dropping ten thousands on an engine with solid mounting. Because those fixtures, call them a "shaft simulator" would fit into the struts or cutlass bearings with near zero clearance taking away the .020 play. Then when you install the actual shaft (because no boat or ship propels itself on an alignment fixture) the .020 would show. Half of .020 is what Matthew? And, does your compnay re check the alignment when the vessel is once again waterbourne?

I would love to have solidly mounted engines, however I am afraid that 2600 horsepower on each side would crack the marble countertops!

Bob Miller, Viking Yacht Service Center, Florida USA