[Electric Boats] Re: Tartan 27, setting up bearing

 

Paul, Dennis has it nailed in my opinion.
From a mechanical point of view, in some dry land applications, some bearings that might be mounted in the same manner as a cutlass bearing might be of a design to take thrust as well as rotation loads, and it would be easy to assume, as you have done, that the prop hub or boss face provides the thrust, but that is not the case.
In a boat setup, the ICE transmission will no doubt have a thrust bearing on the output shaft. This will likely be in the form of a dual purpose bearing, that can take thrust as well as regular loads.
This, combined with the fixed transmission mounts, will prevent the shaft moving forwards to enable the prop to rub on the tube.
So there should be clearance between the prop and cutlass bearing.
No doubt that in reverse, the same transmission bearing is designed to take a thrust load in that direction as well.
So you should be replicating that, I think. I have never seen details of which bearings electric boats use, but it should take forward and reverse thrust, as well as supporting the shaft as a regular bearing.
If you look at car cam belt setups, most have a separate disc like a large washer that is assembled right next to the toothed crank pulley. It has a 'curved-away' edge to prevent belt rub at the outer edge, but will effectively stop the belt sliding off the pulley, and some installations have one on both sides of the pulley, others have it only one side, but have a similar shaped, 'curved-away'(but larger diameter) part on the other side. But this in no way means that this is meant to take thrust, presumably merely to guide the belt. Only one pulley in the drive train has this feature, the camshaft pulleys have open sides.
The amount of play in a suitable typical industrial bearing would be just a few thousandths. Perhaps other group members who actually have bearings in use can give the make and parts number, so that the specs can be looked at.
Sorry if I confused things in my original response post where I had incorrectly assumed that there was a top bearing in the tube. From the descriptions of other members, it is simpler than that.
Hope this helps,
John

--
_______________________________________________
Surf the Web in a faster, safer and easier way:
Download Opera 9 at http://www.opera.com

__._,_.___

Reply to sender | Reply to group | Reply via web post | Start a New Topic

Messages in this topic (10)

Recent Activity:

• New Members 20
• New Photos 1

Visit Your Group

Switch to: Text-Only, Daily Digest • Unsubscribe • Terms of Use

.

__,_._,___