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Old 23-11-2019, 16:20   #1
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Align in water?

Forgive my ignorance, rebuilding an old Pearson 390... Have a new transmission old Perkins 4108 aligning the shaft on the hard to Splash it, but with advice will realign in the water? And how do I go about realigning in the water something I have found no information on. Seems counterproductive to remove the packing gland and try to reset the prop shaft if there is a lot of settle in the boat, have been on the hard for about 8 months.
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Old 23-11-2019, 16:24   #2
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Re: Align in water?

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Originally Posted by hooch View Post
Forgive my ignorance, rebuilding an old Pearson 390... Have a new transmission old Perkins 4108 aligning the shaft on the hard to Splash it, but with advice will realign in the water? And how do I go about realigning in the water something I have found no information on. Seems counterproductive to remove the packing gland and try to reset the prop shaft if there is a lot of settle in the boat, have been on the hard for about 8 months.
Align the engine/tranny to the propshaft, no need to remove the packing gland.
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Old 23-11-2019, 16:54   #3
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Re: Align in water?

I actually understand your difficulty, on our boat the settlement over time of the mounts was such that the shaft was rubbing on the shaft tube. And you can't tell that with the packing gland in place. So, how do you verify that the shaft remains in the center of the tube? Since the packing gland and the engine mounts are all flexible. Short of a bearing to hold the shaft in place you have to guess.

On our boat we aligned (out of the water) with the gland open so we could see that the shaft was in the center of the tube. Then we put a mark on the shaft and took some caliper measurements from the shaft to the hull/keel. Wrote those measurements in indelible ink right on the hull. For port/starboard we just eyeball as we can see down on the shaft/tube, but for up/down we use the measurement. Can detect a change of about 2mm (I'm not a perfect machinist) which still keeps the shaft pretty much in the center (we have 6-8mm annulus). Then align coupling as per normal. We now check once/year against the measurement to see if the engine is settling on the mounts.

[Edit] another technique I've seen, but doesn't work in our space, is to put a laser pointer on the shaft and then mark a target somewhere. In the water you can then check to see if the same pointer has shifted up/down compared with the target. Usually takes a bit of shaft run to make that work, we don't really have the space.[/edit]
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Old 08-12-2019, 06:41   #4
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Re: Align in water?

Thanks! Will take the measurements against the stern tube ring. When I bought the boat everything wasd far enough out of whack that I had to rebuild the inner stern tube since the shaft rubbing had opened a trough in the inboard end.
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Originally Posted by Dsanduril View Post
I actually understand your difficulty, on our boat the settlement over time of the mounts was such that the shaft was rubbing on the shaft tube. And you can't tell that with the packing gland in place. So, how do you verify that the shaft remains in the center of the tube? Since the packing gland and the engine mounts are all flexible. Short of a bearing to hold the shaft in place you have to guess.

On our boat we aligned (out of the water) with the gland open so we could see that the shaft was in the center of the tube. Then we put a mark on the shaft and took some caliper measurements from the shaft to the hull/keel. Wrote those measurements in indelible ink right on the hull. For port/starboard we just eyeball as we can see down on the shaft/tube, but for up/down we use the measurement. Can detect a change of about 2mm (I'm not a perfect machinist) which still keeps the shaft pretty much in the center (we have 6-8mm annulus). Then align coupling as per normal. We now check once/year against the measurement to see if the engine is settling on the mounts.

[Edit] another technique I've seen, but doesn't work in our space, is to put a laser pointer on the shaft and then mark a target somewhere. In the water you can then check to see if the same pointer has shifted up/down compared with the target. Usually takes a bit of shaft run to make that work, we don't really have the space.[/edit]
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Old 08-12-2019, 07:42   #5
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Re: Align in water?

I'm assuming you have a f/g or grp boat, so yes do the alignment in the water after the boat has time to settle in the water. If you think of your boat as a whale and only being supported w/4-6 jack stands (and the keel), once it goes into the water it will be more evenly supported and reshape itself to where it needs to be. IMO would get the alignment somewhat close on the hard (get it roughly centered, but don't fuss too much at this point), then finish it in the water. Don't have any real time period to wait for the hull to settle, but maybe a week(??)

The way it is typically done to align the shaft coupler to the engine coupler is to get the 2 inner surfaces perfectly parallel to each other when you tighten them. Used to use a thin piece of ditto paper (probably something newer) that would leave a mark on the paper where it unevenly hit. Continue motor mount adjustment until you had an even circle.

Once you do it its fairly straight forward.

The adjustment of the standing rigging is similar in the sense that you want the boat to settle in the water before tuning the rig.


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Old 08-12-2019, 08:38   #6
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Re: Align in water?

we have realigned mine while in water not just once but repeatedly as needed. why haul out when something can be done more reasonably in water. engine mounts also can be changed out while boat in water. many issues folks think need haulout are doable easily in water.
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