Engine to Prop Shaft Alignment with boat out of water vs floating?

[Mirror16]

I have a new prop shaft and couplings on my Bristol 45.5 and it's visibly misaligned with the engine/gearbox. The boat is currently out of water, sitting on its keel, propped up in the usual manner. I am being advised that this realignment should be done after the boat has been back in the water for a few days, but for schedule reasons I would much prefer it's done now. I cannot imagine that engine to prop shaft alignment would change very much on a solid lump of a boat like this between it being on the hard and in the water. Comments?

[CarlF]

I would align now. Your boat has a short shaft and no strut - not much to worry about. And it's worrisome that the new shaft is visibly out of alignment. Something may need to be fixed after they try to align and fail.

But when a shaft is changed, it's no uncommon to have to do an alignment more than once to get it right. You can run fine on a less than perfect alignment until it's convenient to tweak it.

More important, find a really good guy to do the alignment. This is as much art as science. It wouldn't hurt to do a rough alignment, then run the engine in gear on the hard for a few minutes to settle things in, then finish the alignment. They can just run a hose into the strainer with the lid off for cooling water. Did you replace the cutlass bearing too?

[Mainebristol]

To your other point, Bristols have way, way thicker layup schedules than most FRP boats, even more than other classic plastics. That thing isn't going to move much, between land and water.
Edit: just realized yours is recent one. Can't say about one built in the '90's. Still, they were always a quality yard. I bet it's just as stiff as an old one.

[a64pilot]

Just as a reference, I aligned my IP on the hard, and then checked it after being in the water for a few days. I could find no difference. I was told it would be fine by the yard, they said lots of boats flex, IP’s don’t.
However some boats do flex a lot. These boats it’s not uncommon for the interior doors to jam when on the hard etc.
On a boat that flexes, it’s seems logical that rig tuning may make as much difference as does being on the hard?

[Q Xopa]

Yes it is good to get as much as you can get done on the hard when you have the opportunity.
IMNHO the best place to start aligning is at the cutlass bearing. If there is excessive play in that, aligning is a non starter. I think most of us would agree that's easier to check on the hard.
As previously mentioned when in the water it may change. Also as time progresses the eng mounts sag so our alignment goes out. This can happen a bit, quite rapidly from new once the engine starts rattling things into place and torque twists things around. It will settle into a stable period until completely worn. Rubber mounts dont last forever.
So also you need to check the condition of your mounts. They need to be good to have/ keep a good alignment.
So it is also good to check it in the water, and a few times after the first few uses for a little while.
My Yanmar, quite typical, is meant to have eng mounts replaced and alignment checked every 4yrs/ 1000hrs.
Most guys, who do their own, check their alignment by disconnecting the coupling and use feeler gauges in typically 4 places.This is more or less ok, certainly better than nothing. Nothing, or not often enough is more the norm.

However by far the quickest and most accurate is using Dial indicators. Obviously a set of Dials and fixtures is more than set of feeler gauges. In my experience anyone with this set up, being that there aren't many secrets among cruisers, is frequently invited to check fellow boaters.

The feeler gauge method does have some limitations and is slower.
It doesn't measure shaft offset too well. It mostly measures angles. You need to measure and adjust both Angle and Offset to do it properly.
It's slow because its adjust and then check. Using Dials its live so you can see as you are making the adjustment where your zero point is etc.

Just my 2 cents.

[a64pilot]

Also alignment changes when the engine applies torque to the drive line.
Watch one, one side will rise up as of course it rotates the prop in one direction, the engine tries to rotate the other. Drag racing we used to chain the left side of the engine down to resist this.
If I had known I was going to install the Sigma Drive, I may have gone to softer mounts, cause with it the engine can move around as much as it wants and it won’t affect alignment. Of course the mounts still have to absorb thrust.

[Q Xopa]

Driveshaft alignment an Art.

IMO, I think you're unfortunately right. It does seem that the process is a Mystical black art to most people.

However although the process is actually not so complicated, or a secret, it seems to be that it is not very widely understood.
Most people just seem to assume they understand and blunder along. If they took some time to find out how to do it correctly, which is not that difficult to find, it would be far less of an ’Art’ and there wouldn’t be so few capable alignment guys around,

This is simply a relatively straight forward, logical procedure. The base principles can be learnt and well understood in maybe 2 hours invested by anyone willing to seek the answers and of average practical mechanical ability. I would say a majority of people on here would be in that category.

In fact I would say anyone investing those 2 hours would be more knowledgeable than a fair number of the guys doing it.

Just my not so humble opinion.

[Ken Z]

I had a engine and gearbox recently installed by a reputable shop and the owner of the company would onily install and hook up shaft with the boat in the water shes a fiberglass sailboat, I m pleased with the results. The abnormal weight on land sitting on the keel is grossly different than in the water.

[akprb]

SOOOOOOO IMORTANT this is done right!

Yes, align on hard but be sure to check/align again once in water.

Believe me, believe me :-)

[Q Xopa]

Yes it is important.

If it isnt good your Cutlass bearing and engine mounts will have more load on them than ideal. This will mean more/ faster wear than ideal.

It will also most probably mean more noise and vibrations which will wear crew and other boat components at a faster than ideal rate too.

You might get away with it for a while, like many do, until you dont.

OK when to align, take your pick. As mentioned as long as it is finally confirmed in the water.

However checking the Cutlass, and if required replace, is an out of the water job. This should be the first step in a driveshaft alignment.

[JOHNMARDALL]

If your shaft is only supported at the cutless bearing and the gearbox flange, when it's not connected to the flange, depending on its length, the shaft may have quite a bit of angular movement even with a new cutless bearing. To control that and center the shaft in the log, where it comes into the engine space, I roll masking tape around the shaft to make a temporary collar that plugs into the shaft log. With the shaft centered in the log, you can then proceed to line up the engine/gearbox assembly using methods already described by other contributors. Obviously, this can only be done on the dry, as the shaft log is open.
If the boat is fitted with a drip-less type shaft seal, with a hose-bellows connection to the log, when you've put the boat in the water and allowed it to settle, you can't see if the shaft is still centered in the log, so I have a gauge board, that notches over the shaft and lines up with marks on the engine space bulkhead, so that I can still see if the shaft has moved from where it was when the boat was on the dry.

Oh- and I use a flexible coupling between the shaft and gearbox to give me a little bit of forgiveness for my limited skills and patience.

Hope this helps- good luck
John Mardall
Vetus Maxwell Group

[Cheechako]

You can do it out of the water and see when it's back in. Normally do it in the water, but it MAY not change that much. However, in order to find out if it's good in the water, you are pretty much doing the job again anyway. OTOH, if it runs smooth and looks smooth, maybe not to worry. Probably most boats out there are not that close. How long will a boat stay in alignment I wonder? The whole system is flexible.

[Cadence]

Originally Posted by Mirror16

I have a new prop shaft and couplings on my Bristol 45.5 and it's visibly misaligned with the engine/gearbox. The boat is currently out of water, sitting on its keel, propped up in the usual manner. I am being advised that this realignment should be done after the boat has been back in the water for a few days, but for schedule reasons I would much prefer it's done now. I cannot imagine that engine to prop shaft alignment would change very much on a solid lump of a boat like this between it being on the hard and in the water. Comments?

I'd only do a rough alignment on the hard /hill. True it up once in the water.

[Q Xopa]

Yes both good points.

Ensuring the prop shaft is in the center of the cutlass as much as possible at the coupling. I have seen people use a machined tapered nylon plug in the stern tube with no dripless.

I use my dial to feel where the shaft has max up, down, left and right. Then split the difference with my dial readings. This is for the shaft angle changing in the Cutlass. There will always be some movement in the Cutlass to prop shaft.

What is more important to ensure there is minimum play is up and down radial play. If this is sloppy there is literally nothing to align the engine to.

Yes also correct that even sitting in the water with the hull sitting 'naturally', ie not flexed potentially awkwardly from the keel pushing up and the hull hanging down. This is opposite in the water. The question is how much it changes is different for different boats.

I can see the point of the earlier comment about leaving the coupling disconnected until after in the water. I agree this may be the most conservative/ safest approach so I cant be critical of that.

Doing our alignment in this situation is all potentially changed when the there is differing torque and thrust applied from the prop when operating. Also when the boat is healed over that heavy bit of iron wants to lean over too on the rubber mounts.

in a past life I used to align helicopter tail booms for the same reasons, ie driveshaft alignment. Which again the manufacturers recommend. However we know how much a tail boom flexes in flight with differing tail rotor thrust, horizontal stabilizer loads and g loads etc imposed in different stages of flight. It is quite scary to see this in flight. It is more or less an over sized flimsy coke can construction.

I guess keeping this all in perspective the idea is to get it as good as possible to give it a fighting chance to minimize the effect of all these other factors. The name of the game is minimizing misalignment. If we can do this then we are ahead of the majority who are blissfully unaware.

It's not a perfect world we live in.

[onavegador]

My last monohull had a very long shaft. And after my first hauling I had to align engine and shaft, even nothing was done on engine and shaft.

So I aligned shaft and engine when the boat was back in the water.

Fair winds
James