Rudder bearings

[connor_carson]

Hi all,
I'm replacing rudder bearings on a Hurley 18 - a 1 inch rudder shaft passes through a metal tube in the stern locker and out to an unsupported spade rudder. The tube itself is corroded so I will replace the whole assembly. I was advised to use a cutless bearing as the lower bearing in my new tube - this looks like a bronze metal sheathe with a water lubricated rubber lining which is a kind of star shape in cross section. Upper bearing (not in water) to be nylon bush or similar.
I'm having second thoughts about this idea - will the rubber insert in the cutless bearing be sufficiently rigid to stop side to side play in the rudder? And is it really a good idea to put the outer bronze sheathe in contact with the wall of the new rudder tube (planning stainless steel) and then dunk the whole lot in sea water?
Any advice or superior plans would be gratefully received.
Connor C.

 

[boatmike]

Its an often used solution. The cutless bearing is designed for propshaft use really and often set in a stainless steel tube with a stainless steel shaft so not really a problem. As far as loads are concerned it will take a lot more than you will impose on your little Hurley.
Great little boat by the way. Took one to the Scillies once a long time ago. Proper little yacht!

 

[eyehavit]

C_C

I agree with Boatmike in that rubber bearings are designed for prop-shaft applications. High turning speed shafts promote hydro-dynamic lubrication. Where these conditions exist, there are relatively small axial forces and rubber works fine. However, a rudder bearing is an application where high radial loads can exist, so it makes sense to look for a stronger bearing material.
There are a number of reasons.
The length of the bearing can be significantly reduced without compromising overall strength.
For example, say on a 1" dia. shaft, using a 25mm long hard non-metallic composite type bearing. it is entirely possible to subject that bearing to more than ten tonnes of axial load before it fails.
Shorter rudder bearings enable shaft support to be closer to the load so contribute to overall shaft straightness, less shaft drag and overall better feel.
Hope this helps.

 

[boatmike]

There is absolutely no way that the sideways load on a Hurley 18 rudder bearing could approach 10 tonnes. Come on! The boat is 18 ft long! Anything like that load would snap the little rudder like a carrot. A cutless bearing is a very reasonable solution and if it does wear it's easily replaced.

 

[eyehavit]

C_C said :..............."I'm having second thoughts about this idea - will the rubber insert in the cutless bearing be sufficiently rigid to stop side to side play in the rudder? And is it really a good idea to put the outer bronze sheathe in contact with the wall of the new rudder tube (planning stainless steel) and then dunk the whole lot in sea water?..............."
C_C is asking for options/advice. I am providing exactly that.
The cost of buying a composite bearing say 2" long is reasonable, probably cheaper than a 4" long bronze backed rubber bearing.
A composite bearing completely avoids C_C's concern about galvanic corrosion between the bronze and stainless, regardless whether that concern is real or perceived.
It will deliver an easier and more positive steering feel than rubber.
These are tangible advantages to assist someone to make a logical selection.
In my opinion it is a better choice than rubber for a rudder bearing.

 

[connor_carson]

Many thanks for the advice ... I'll think it over.
Cheers for now, Connor C.

 

[georgesoilis]

Oil lublicated shaft???WAS:Re: Rudder bearings

So how about the OIL LUBLICATED SHAFT (bearing rather ) that i have on my Bostrom 31 sailing yacht.
It came with the YAnmar 12 hp 1977 built ,and it aseemsa lot more advanced than the cheapo grease lublicated ones.
But there is only one problem.
I do not have any info on the make,the oil i should use,or how often to vchange this oil,i dont know if i should top it up ad to what level,in other words i need any info on this i can get.

 

[eyehavit]

Re: Oil lublicated shaft???WAS:Re: Rudder bearings

George.
I am going to assume your oil lubricated bearing is for a propshaft.
If you cannot get that information from the manufacturer take a small sample of the oil and have it analysed. Also have the viscosity determined. I expect you will find it heavily contaminated with seawater.
Given the age you may also want to check whether the aft seal is actually keeping out water. Unless the boat sees frequent service, barnacles and other sea-growth destroy seals resulting in oil slowly seeping into and polluting the water. /forums/images/graemlins/frown.gif
If I am correct with the above when the opportunity arises you may wish to convert to water lubricated bearings.