Shaft Alignment Question

[BobL]

Is it possible to check shaft alignment with boat in the water?

BobL

[zboss]

I think that is the preferred method.

I did mine recently and it seemed to work out OK. Its my understanding that you cannot do a proper alignment on the hard because the boat will take on a slightly different shape when its floating. So, you can align all you want on the hard but it won't be correct.

[BobL]

Thanks for the quick reply. Next question is "how is this done?" I've never aligned a shaft before

[svlamorocha]

Originally Posted by BobL

Is it possible to check shaft alignment with boat in the water?

BobL

Sure. When you build a boat or change engine on the hard you do a preliminary alignment out of the water but the one that matters is the one you do in the water. All that said, for the guy or girl doing the alignment the work is the same because all the work is done inside.

[skipmac]

Checking in the water is the correct method. Out of the water the shape of the hull and thus the alignment will change.

The only way I know to accurately check the alignment is to put a feeler gauge between the two halves of the flange which will involve loosening the bolts and separating the flange. Then put a feeler gauge in the crack at 12, 3, 6 and 9 o'clock. Should be within a few thousandths, 0.05" if I recall but would have to look at my notes to check that.

[BobL]

I see. How can it be adjusted if its off more than 0.05?

[exMaggieDrum]

On most boats (I am familiar with) you have to adjust the height of the engine/transmission on the motor mounts. This changes the angle of the engine/transmission relative to the prop shaft. You don't adjust the prop shaft itself. It is what it is. But this can be a very challenging job, requiring a good mental ability to imagine the geometry of the engine and the effect of each adjustment to the alignment. And you have to be sure and lock in the adjustment after it is done (and check again).

It can be very tedious with lots of trial and error. But it is doable with patience. Make sure you motor mounts are in good condition while you are at it and replace if shot.

And the prop shaft mounting plate has to be seated right and tight before you start. It has to be dead nuts perpendicular to the prop shaft itself or it will be worse.

You can rough adjust on the hard but the final adjustment should be done in the water as noted.

[BobL]

Thanks so much for the great info...I'm going to work on it!

[Cheechako]

Originally Posted by BobL

I see. How can it be adjusted if its off more than 0.05?

I think that's a typo... should be maybe .005 (five thousanths) But .010 is fine in my book. it can be tedious. You not only need the gap to be uniform, but the flanges need to be concentric. ie: center of the shaft to be aligned with center of the engine output.
You get there by raising/lowering the engine mounts to get both acceptable. This will require adjusting both fore and aft mounts often. If the gap is not uniform port/starboard, you may have to loosen the mounts and shift the engine... depending on mount type.

[Wotname]

Originally Posted by BobL

I see. How can it be adjusted if its off more than 0.05?

Have a look at this thread, especially the link in post 5.

http://www.cruisersforum.com/forums/...ft-139357.html

[Lepke]

.002" is correct and achievable, some yards would like you to believe .005 or .010 is ok. Slack the flange bolts. You use any combinations of feeler gauges to measure the difference as you go around the flanges. Turning the shaft shouldn't change where the tightest spot is. Assuming a standard installation: If the tightest spot is on the st'bd side of the flange, either the engine front needs to go to port or the transmission needs to move to st'bd or some combination. It won't be that simple. The tight spot rarely is at the exact top, bottom or sides. Too much misalignment (.005"+) will cause bearing wear, either the stern bearing or the rear transmission bearing. In some older transmissions, internal splines will wear. Sometimes when down inside a silent hull you can hear a thumping sound in a passing boat with a missalignment. It also scares the fish if you're trolling.