Prop shaft alignment: on the hard or in water?

[jmschmidt]

Both. On the hard for a close fit, splash, then wait a few days and do a final.

[Ken Z]

In the water, so the boat is supported the way it was designed.

[Locquatious]

I used to align lasers w/four legs. It is amazing how similar aligning an engine is.

On the shaft end of the engine note the misalignment distance horizontal and vertical. Then move the shaft end of the engine 1.5 (that is to alignment [1] and then in the same direction an additional [.5]) times those distances. Next move the back of the engine such that the isolator plates are square all the way around. Next go back to the shaft end and again note the misalignment distances. Adjust the shaft end of the engine 1.5 times those distances. Then square up at the rear of the engine. Keep going back and forth this way till the alignment is satisfactory.

The 1.5 times adjustment approach will reduce the number of iterations significantly.

[Cadence]

Originally Posted by Cheechako

It MAY not matter. You wont know how well it stays as set unless it's checked in the water. That's not a bad price for what he quoted.

I went back and reread the OP and would agree that the price does not sound out of line considering the cutless replacement.

[Lepke]

My father was a chief engineer and taught me shaft alignment when I was about 13. I'm 70 now and have always done my own alignments. Sometimes with an engine or bearing change I have allowed the yard to do the alignment, but I always check. Most yards don't adjust as close as I do. They don't always send their best person to do the alignment. I find about half the time it's off. When I had a yard I fixed many alignment problems started in another yard. A misaligned shaft will cause premature wear in the stern bearing, the rear transmission bearing and sometimes the shaft itself will wear in the stern bearing and seal.
Also, the latest labor saving alignment coupling doesn't always work as advertised. A shaft with a single u-joint has to be aligned as close as a shaft without one. With 2 u-joints it can be a loose alignment, but if so will cause noise in the hull.

[TCL]

Pretty sure the answer is both. You'll do, or have the mechanic do, an initial alignment on the hard, but you definitely want to check the final alignment once it is splashed. I just replaced the transmission and while I removed the transmission, prop shaft, thrust bearing, and shaft seal, and reinstalled the transmission and shaft seal, myself, I put in a work order to have the boat yard remove and reinstall the cutlass bearing and to do the shaft alignment (after confirming that one of the guys had the requisite experience and reputation). The payment for alignment is for doing it on the yard and checking/finalizing once it is splashed. For comparison, the cutlass bearing removal/replacement was about 3 hours of labor, in part because a set screw had to be drilled out. The prop shaft alignment should happen this week. I can update with the total time if helpful.

[ferrailleur]

Originally Posted by jasbee

MUST be done in the water. It depends to a degree on the hull material but it should always be re-checked once in the water. We had a wooden carvel built yacht and thought that the engineer/cowboy had done the job properly (in Krabi, Thailand), but he did not do this and we had endless vibration issues until we finally figured out the problem.
You also need to be there to make sure things are done properly. This knowledge from hard-won experience.

Thanks
Nobody touch my boat unless I'm there!

[sailorboy1]

While I feel alignment is of course important and would check it once in the water. I doubt all the effort to try to "get it just right" is worth it. Once the prop is turning and pushing the boat the shaft changes position and the engine mounts "give". Then there's waves, speed flex, prop fouling and balance etc etc etc.

I know I'm going aganist the grain and aren't going to fight back when the arrows come my way, but spend some time a research it.

[Cadence]

Originally Posted by sailorboy1

While I feel alignment is of course important and would check it once in the water. I doubt all the effort to try to "get it just right" is worth it. Once the prop is turning and pushing the boat the shaft changes position and the engine mounts "give". Then there's waves, speed flex, prop fouling and balance etc etc etc.

I know I'm going aganist the grain and aren't going to fight back when the arrows come my way, but spend some time a research it.

You may have a point depending on the type of motor mount.

[Scrimshaw4]

You raised 3 issues regarding your shaft. 1) What is the condition of your cutlass bearing / when was it last replaced? If needed, now would be the time to do it. 2) What is the condition /last time your shaft log was repacked? If needed, now would be the time to do it. 3) Shaft alignment would be started on the hard and then finished in the water. How you do this or who you contract is up to you. JMHO

[boatman1]

Sailorboys' point is valid, but it's not a waste of time to get it aligned as well as you can. If the current installation includes flexible engine mounts that have some age on them, replacing them with new "firm" mounts might be in order. My"seat of the pants" engineering says that if you do have flexible engine mounts then you should also have a flexible shaft coupling to allow for the engines' slight movement under load. There should be two people to do the aligning, as it' awfully time consuming and exhausting for the poor mechanic actually measuring the coupling gapping to have to crawl out of that position to move the engine around. Depending on the accessibity to the coupling, an alternative to using feeler gauges or slips of paper to measure gaps is to "tap tune" it. Lightly tapping the outboard edge of the coupling flange with preferably a bronze hammer will return a discernable difference in tone where the adjacent faces don't touch. You should check alignment again after launch.

[mjgill1]

Originally Posted by sailorboy1

While I feel alignment is of course important and would check it once in the water. I doubt all the effort to try to "get it just right" is worth it. Once the prop is turning and pushing the boat the shaft changes position and the engine mounts "give". Then there's waves, speed flex, prop fouling and balance etc etc etc.

I know I'm going against the grain and aren't going to fight back when the arrows come my way, but spend some time a research it.

That's an interesting point. I'm detail oriented (anal retentive) so I like to know that it was done right. Then all I have to blame when things go wrong is the equipment.
When I was doing the alignment, I learned that one of the motor mount bolts was stripped. Fortunately, I was able to get a washer and lock nut installed. The bolts were simply tapped into the fiberglass. Boat ownership is definitely an intimate experience. I know practically every nut and bolt on our boat pretty well.

[Sailmonkey]

Originally Posted by sailorboy1

While I feel alignment is of course important and would check it once in the water. I doubt all the effort to try to "get it just right" is worth it. Once the prop is turning and pushing the boat the shaft changes position and the engine mounts "give". Then there's waves, speed flex, prop fouling and balance etc etc etc.



I know I'm going aganist the grain and aren't going to fight back when the arrows come my way, but spend some time a research it.

I do feel compelled to agree with you here.

When tied to the dock and I mash the throttle down I can visually see the back of the engine squat with the thrust from the prop. Guaranteed the alignment is out of kilter like that.

[JOHNMARDALL]

The conventional wisdom, that shaft alignment should be done after the boat has been in the water for a couple of days and settled into shape, with the stays and shrouds tight, is correct but easier said than done.
Most monohull sailboats have the engine space under the cockpit, rendering the shaft seal/stuffing box very difficult to get at or even see. In addition, the shaft is usually supported by only one bearing, the cutless at the outer end of the shaft log/stern tube.
Alignment involves centering the shaft in the inboard end of the shaft log and then aligning the engine-gearbox assembly with that shaft position. However, if the boat is fitted with a modern dripless shaft seal (PYI, etc.) connected to the shaft log by a flexible hose, once the boat is in the water, you can't take the shaft seal off to see the shaft position in the log without flooding the boat.
I overcome this by doing the alignment on the dry and marking and measuring the shaft position on a wooden gauge board, set between marks on the engine space bulkheads and located above a section of the shaft still visible when the shaft seal is in position. Once the boat has settled in the water, I put the guage board back into place and can see if the shaft has moved in the log. If it has, I disconnect the drive flange, re-center the shaft on hanger wires from the gauge board and re-align ( a huge pain the butt, but necessary)


I hope this helps, please feel free to contact me at jmardall@comcast.net if you need more information or for a discussion.


All the best
John Mardall
Vetus Maxwell Boat Equipment

[Rob.Lovelace]

how do you maintain the seal on a PPS when doing a shaft alignment in the water?