Re: Ang.:Re: [electricboats] Material Choices and Thrust Bearings

The double spherical roller bearing from grainger looks fine.

Even a smaller bearing than the shown will be fine for your 12KW motor...

I found an old thread in boatdesign.net. Please see reply #6 from the honorable Mike Johns:

https://www.boatdesign.net/threads/smaller-vessel-thrust-bearings.46072/

I guess not feasible to make housings, when they already exist.

In the above thread, there are suggestions for housings too.

If in doubt, call SKF tech. dept. They are actually nice guys !

For ease of lubrication, they make these bearings in sealed versions too.

I would be happy by fixing the housing to the base plate properly aligned with shims (or ChockFast), and thus avoid a flexible coupling. (The belt drive should be flexible enough in itself.)

However, it takes a sturdy design of frame and base plate.

In my case, I will first try to modify my old saildrive to avoid a change to shaft drive (hellofwork).

Dan, from your photo, your lathe seems to be underpowered for this kind of shaft turning, IMHO.

On Friday, 26 March 2021, 23:07:08 GMT+8, Dan Pfeiffer <dan@pfeiffer.net> wrote:

Some more on thrust bearing specifications...

My boat came with a Volvo 23HP diesel and a Walter RV-10D v-drive that contained the thrust bearing.   The Walter RV-10 is specified for 2HP/100rpm or 48hp at 2400 (the max RPM on the Volvo).  So that's about double the capacity needed with the Volvo.  The thrust bearing in the unit can be seen in this drawing.  It is part number 15 (sorry for the silly long link...). 

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.moyermarineforum.com%2Fforums%2F%2Fattachment.php%3Fattachmentid%3D14693%26d%3D1575224869&psig=AOvVaw3BxXBt2iXbDdDJ4lHXYFXj&ust=1616798626542000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCOj3l7LCzO8CFQAAAAAdAAAAABAJ

It is a double row angular contact ball bearing type 5304.  

The bearings in the trailer hub I have been considering are L68149 and L44649 tapered roller bearings.  

I found some load specs on all these bearings in this document:
https://blog.misumiusa.com/wp-content/uploads/2019/01/NSK_CAT_E1103_partC_Ball_Bearings.pdf

Basic Load Ratings (radial)
   type   -               Cr              -        C0r
  5304  - 24,600N (5530lbs) -  15,000N (3372lbs)     v-drive
68149   - 35,000N (7868lbs)  - 47,000 (10,566lbs) trailer hub large
44649  -  27,600 (6204lbs)  -   32,000 (7193lbs) trailer hub small

The second figure is a static load rating. 

I also found this regarding axial loads in deep groove ball bearings:
http://www.rbcbearings.com/ballbearings/axial.htm

Deep groove ball bearings by nature of their design can
carry axial loads either alone or in combination with radial
loads. Axial load capacity of standard bearings is 0.5 times
the Basic Static Load Rating, C_O of that bearing. Smaller
bearings should not be subject to a load greater than
0.25 times C_O. Excessive axial loads can lead to serious
reduction of bearing


I am not sure how all this relates to the bearings in the trailer hub or v-drive but I am thinking the bearings in the trailer hub are at least as strong as the bearing in my v-drive.   The trailer bearings are tapered roller bearings which I think are supposed to be better suited than the ball bearings for axial loads?  I don't know if that makes the trailer hub assembly a reasonable thrust bearing or not.  But at least the bearings are up to the task?   And from this is it possible that the trailer hub is actually stronger as a thrust bearing unit than the v-drive that was running in my boat for 43 years?     I am sure there is more to it all than that.  But there are some numbers to consider. 

But, another relevant consideration with the comparison between the angular contact bearings (v-drive) and tapered bearings (trailer hub) is friction.  The angular contact are lower friction and in a housing set up to run in oil rather than grease (my v drive is filled with 30wt oil) maybe they would be a better choice with less power lost between the electric motor and the prop.   Now we just need an appropriate housing.  And that's really what the trailer hub was about. 

Are the double roller spherical bearings something in between the roller and the angular contact? 

I don't know the answers to these questions but I'll keep researching. 


Dan Pfeiffer

On 2021-03-25 5:17 pm, Dan Pfeiffer wrote:

Carsten,  Thanks for the useful details. I have googled it.  Many hours spent.  I should have said I was a hobbyist, not a novice.  I don't have the knowledge on materials but I have some experience with the machining.  I have a very capable Sheldon 11" lathe with the appropriate tooling for this and a Bridgeport.  Worst case is I waste the 30-$50 on a blank for some useful practice.  It is a more challenging fabrication but worth a try I think. 

The spherical bearing is very interesting.  Maybe something like this:
https://www.grainger.com/product/SKF-Spherical-Roller-Bearing-36MD98

Not crazy expensive but there is still the housing.  And that will need to have lubrication and seals.  I'll look further into it.   Let us know when your housing design is ready. 

Yes the shaft will be in the engine room.  No exposure to sea water unless a hose bursts.  And I am on fresh water. 

Thanks, Dan Pfeiffer

 

On 2021-03-25 3:04 pm, Carsten via groups.io wrote:

Dan, 34CrNiMo6 is for hard working shafts, and easy to machine in properly sized lathe, given the right treatment is done before machining.

It is NOT stainless steel, and thus, not prone to "self-hardening".

Please google it.

 

I don't know your machining skills, but please contact a shaft machining shop (I did not say ANY machining shop) with your design at hand. This is definitely not a DIY novice job.

 

There seemailer wheel hub bearings lately in this forum, mostly triggered by the Thunderstruck (etc.) base plate designs.The shaft of a propeller has mostly only (bi-directional) axial forces, exept where we cons to be a tendency to choose standard trnect our belt pulley.

A hub bearing is meant to deal with radial forces, and some axial forces.

There are torsional forces too.

My suggestion is to use a double roller spherical bearing, set in a proper housing.

I contacted SKF (the inventor), and they recommended this bearing for this purpose.

(Hmm, maybe I should mass produce a range of housings ? ;-)

 

For corrosion, Dan, your shaft is to be in the engine/motor room, and not submerged (I hope), so it should only be protected for exposure to humidity, like a car body.

A clear Dinitrol spray will do fine.

Priming and painting looks nice, but ehh, not necessary for a simple shaft, right ?!

 

I hope this information will be useful.