----- Original Message -----From: tartan27hull157Sent: Friday, October 01, 2010 8:37 AMSubject: [Electric Boats] Re: Tartan 27, setting up bearingThanks again Denny and Tom and others for these tips & your patience.
It occurred to me as I sketched this up that I don't understand which elements of the system will take the thrust load of the shaft, which is really the whole point of turning the propeller. In forward the shaft should be trying to spear the cabin (until the prop finds out it's too big to get through the cutlass bearing), and in reverse the shaft should be trying to go for a swim.
Is the toothed belt rigid enough to keep the driven pulley aligned with the drive pulley all by itself? Or should the driven pulley be designed to bear against the thrust bearing? This would keep the shaft in the boat in reverse, but I still don't see why the shaft doesn't push itself into the boat in forward, at least until the prop bears directly on the cutless bearing, which I think neither is designed for.
Since nobody has mentioned this, I guess it's designed into the toothed pulleys, probably in how deeply the belt is seated and how it is tensioned, but I would think any fore-aft play in the driven pulley/prop shaft assembly would at least chew up the belts, if not otherwise hurt things.
Hope you can help, Paul
--- In electricboats@yahoogroups.com, "dennis wolfe" <dwolfe@...> wrote:
>
> Sounds like that would work fine with robust tabbing. The flange bearing is self aligning, that is the bearing should be on the correct centerline but the mounting plate does not have to be perfectly square to the shaft in the Y and Z axes. You should try to get it as square as possible though.
>
> Denny
>
> ----- Original Message -----
> From: tartan27hull157
> To: electricboats@yahoogroups.com
> Sent: Thursday, September 30, 2010 10:00 PM
> Subject: [Electric Boats] Re: Tartan 27, setting up bearing
>
>
>
> Thanks everybody for all the thoughts and advice on the bearing.
>
> It sounds like what I was planning to do might not be careful enough.
>
> I was going to fabricate a transverse plate to hold the bearing and fit it loosely in the shaft alley, then mount the bearing into it off the shaft.
>
> Then I was going to mark the current play in the shaft up, down, left, and right; find the center of that play, assume that was where I wanted the shaft to end up...then slide the bearing (already installed in the transverse plate) onto the shaft it and block the shaft at its "center of play" position. Then tab the plate to the hull.
>
> Basically I would be hanging the bearing from the 1in shaft, with the shaft supported forward by blocks and aft by the cutlass bearing, until the epoxy cured.
>
> I used a similar technique when I replaced my chainplate knees--hang the knee from the chainplate until the epoxy cures, to ensure that the knee (and the holes in it) were in the right place relative to the chainplate.
>
> But I am concerned that bearings in the drivetrain need to have better alignment than the chainplate knees did.
>
> I am also worried about doing this out of the water -- doesn't the boat change shape some between the water and the hard?
>
> Thanks again, Paul
>
> --- In electricboats@yahoogroups.com, "Tom" <boat_works@> wrote:
> >
> >
> >
> > Most boats will have self-aligning stuffing boxes (or shaft seals). Just remove the stuffing box and shim the shaft to be centered in the shaft log. In most boats the unsupported shaft is adequately stiff to allow you to accurately place the thrust bearing.
> >
> > This assumes that you have the boat out of the water.
> >
> > It's really not difficult. I've shimmed shafts that only had 3/32" clearance between the shaft and the log without any trouble.
> >
> > -Tom
> >
> >
> > --- In electricboats@yahoogroups.com, "John Green" <v_2jgree@> wrote:
> > >
> > > A way you can go when setting up a bearing is to have it mounted on a plate, with slots or oversized holes for adjustment of the flanged bearing.
> > > Although my own personal choice would be to have 2 bearings, and universal joints and a short drive shaft to drive the actual prop shaft, but whether you have one or two, this setup will work.
> > > The flanges are normally square. You position metal blocks welded on just clear of each of the 4 faces. They are drilled and tapped, and have bolts through them that can be adjusted to butt up against the bearing.
> > > To set up a single bearing, you take a dial indicator, and place it in the vertical position. Set it to zero. Pull the shaft up to it's fullest top position, finding the normal position it would be in if the boat was upside down, that is, do not pull beyond a reasonable resting place. Take a reading of the dial gauge. Say it is 50 thousandths, then you adjust the screws in the appropriate block, in this case the bottom one, and raise the shaft/bearing up by 25 thousandths, then repeat the process for sideways play, pulling to one side, (like gravity did when doing the vertical one) zero out the dial, then pull the other way take a reading, set it up by splitting the difference of the two readings. then tighten the main holding bolts.
> > > You can still do this without the blocks and screws, but they make it easier. They are also a way to maintain the bearing position if the main attachment bolts work loose, buying a bit of time. If you prefer not to have them, try pinching up the flange bolts hand tight, then tapping the bearing flange sides to move it in small increments once you have the readings.
> > > A far better way is to have 2 dial indicators. Then you can be sure that one axis does not move when you are setting up the other. But you can manage with one if care is taken.
> > > The idea behind this is that the shaft itself ends up in the centre of all the surrounding clearances that are currently there.
> > > This info comes from experience as a machinist/millwright and may have snags due to the marine application, I have only just got into boats, so other group members might wish to correct errors/opinions.
> > >
> > > My own personal preference will be to separate the prop shaft, and have the drive through a short drive shaft. I am assuming that the prop shaft has two bearings, one each end of the tube. To have 3 of 4 total on the same shaft is mechanically unsound from a practical sense, particularly if the mountings are likely to flex, such as with a boat hull.
> > > If that is the way you choose, you might be better with two plates to support the motor(s) and bearings, to enable side load without impacting the prop shaft.
> > > Maybe also take a look at fabric universal joints such as are sometimes used in automotive steering on some older vehicles, they are forgiving, and would probably reduce vibration, and require less maintenance than regular UJ's, although of course there would be power limitations, however, they were used for the main drive on pre-war Fiat Topolino cars, so that would indicate a capability of at least 20HP.
> > > I would also favour the motor(s) being mounted from behind, allowing easy access to the drive belts.
> > >
> > > --
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