Bearings instead of bushings. Makes a difference?

[JackBlack26]

I was looking at possibly installing some bearings in the struts of all the boats I own. Would it make a difference just for playing on the water? Not racing right now, just trying to make my systems as efficient as possible.

If so, what type are best? Sealed metal or rubber? Chrome bearings? Stainless? Ceramic balls?

Thanks in advance

[Fluid]

I would say not to use ball bearings for sport use. Lead teflon bushings or sleeve bearings work just fine, in fact I have set all my SAW records with L/T bushings. While ball bearings might supply a marginal speed difference (I'd like to see scientific evidence supporting this), they are more costly, require regular maintenance and eventual replacement. Unless you are a gluton for punishment, KISS.



.

[T.S.Davis]

Plus, the ball bearings are not very forgiving when your prop is out of balance either. They're great if everything is perfect but keeping everything perfect isn't easy. With a bushing it shows wear before it gets too bad. With bearings they just give up the ghost on you......surprise!!!! At least for me they did.

[JIM MARCUM]

If you are running a 1/4" prop shaft there are twin SS NEEDLE bearing stinger & regular struts available. Ball Bearings (and bushings) don't handle axial displacement loads well, and BBs have a larger OD by design. That's why Automotive piston wrist pins have needle bearings. For FE boats, bushings require minimal maintenance & have minimal shaft drag when lubed well. In theory, needle bearing have a slight advantage with less shaft drag & will outlast bushings by far. In reality, bushings are cheap. EZ to replace & nearly as efficent as needle bearings. Listen to the SAW guys. JIM

[siberianhusky]

More drag with bearings underwater
M_drag = V_MK_balld_m ⁵n² this is the formula for calculating bearing drag in an oil bath, change the viscosity to that of water and it will work the same as for oil.
When the shaft is spinning in a bushing it is floating in a thin film of oil and water and shouldn't be touching the bushing at all (in practice unbalances in the drive system cause things to have some runout).
While a ball/roller/needle bearing may feel smoother at low rpm (turning with fingers) at speed a bushing underwater will have less drag on the rotating shaft.

[properchopper]

I've tried BB struts in two boats. Expensive, need frequent replacement. Tricky to install so they stay in place; once removal (for replacement) goes wrong with the outer race stuck in place you have ruined the strut. Ask me about that one .While there may (or not) be a theoretical advantage with BB, I'm now a big fan of lead teflon. I know that Randy has some nice BB struts, maybe he has found the right combination.

[Jeff Wohlt]

Nothing floats in a "thin" layer of water and oil unless it has no prop on it. Side torque from rotation will always put pressure on your bushing. Bearings will not have the resistance under this scenario as a busing will. Water is a great lube as long as you can keep it directing on the sahft. Just because our boats run forward does not mean water is on the shaft. Good discussion but I really do not think your formula applies to this.

[m4a1usr]

John

[siberianhusky]

Cool, But I'll stick with what the SAE folks who come up with this stuff, write the papers and numbers to back it have to say.
ALways been my policy to go with where the actual mathematical proof is.
There is a very interesting white paper put out by SKF Bearing on this exact subject, check it out sometime.
Have a good day.

[NativePaul]

A good racing buddy of mine puts a water inlet and outlet on his struts and runs his water cooling tube through it on the way to the hull to try and keep his shaft floating, its a great idea but I see no way to test it really, if he removed the water tube I doubt it would make a big enough difference to be measurable beyond statistical error, and the same if he tested one of my BB struts, any speed differential if measureable is as likely to have come from not being able to get the strut in exactly the same place as any increase or reduction in shaft friction. I will just say that I have used both lead/teflon and BBs extensively and both work well.

[antslake]

Where do you buy these bushing? Do they make them in metric sizes?

[NativePaul]

OSE sell 1/8 and 3/16, not sure who sells 4mm, I'm sure they are available but for 4mm shafts I use BB struts, loads of places sell 4x7x2.5mm BBs

[Jeff Wohlt]

I do not doubt introducing oils and different weights changes resistance in a bearing...of course it does. I will read the paper but if that was the conclusion then certainly it would make sense...heavier weight oils are certainly going to makes diiferences in a bearing. I am not a staunch bearing user but I do think they work well and sleeves were only used in old systems such as electric motors or other high end components. To each his own I guess. I sell plenty of sleeve bushings so that may say something.

[Darin Jordan]

I personally think that Bearings when using a wire-drive ARE an advantage... The wire, otherwise, forces the stub-shaft into the top of the forward bushing, and into the bottom of the aft bushing...

I haven't build any 3/16" ID sized struts with bearings yet, but on all of my 1/8" OD stub boats, I use stainless or ceramic bearings. It's not that big of a deal to work with for the types of boats these are (2-Lap/SAW)... For heat racing on a regular basis, I'd likely just run flex cables and lead-teflons...