Rudder bearing (again)

[isandell]

I know that the subject of rudder bearings has been discussed here before, but I think that my query is slightly different.

Three years ago I got some bearings made from what I was told was the correct material (I believe a type of nylon). After a few months they tightened up and at the next scrubbing ( a year after fitting the new bearings) I dropped the rudder and eased the bearings again. All seemed fine.

Over the next year, the bearings tightened again. The boat is now out of the water again and I am wondering whether to ease the bearings again, or replace them with something else. It's now nearly 3 years since the bearing were replaced. Will they have taken up as much moisture as they are going to, or will they continue to swell?

Ian

 

[eyehavit]

Ian,
Where humid conditions and direct contact with water occurs nylon is unpredictable. Nylon can absorb water up to 10% of its mass, along with resultant dimensional change.
Heavy-wall bearings immersed in water can take a long time to completely absorb moisture. They continue to change dimension until saturated with moisture. This can only be exacerbated if the bearing is prone to moisture swell as well as exposed only intermittently to water.
Whether you decide to persevere with your existing nylon bearings and get lucky 3rd time 'round or decide to pull them is your call. I guess a lot depends on how difficult they are to remove and replace. /forums/images/graemlins/frown.gif
There are a number of purpose made materials that exhibit very low to neglible moisture swell and suitable for use as rudder bearings.
You may wish to check this website www.maritexbearings.com

 

[JOHNOO]

If it.s a Dehler send me a PM

 

[boatmike]

I agree that Nylon is not a material that should ever be used for rudder bearings but it's not unpredictable. It's highly predictable being very hydroscopic. It WILL swell up!!!! Sorry to nitpick though Richard. I agree with you in principle!

 

[eyehavit]

boatmike,
You are correct. Nylon is indeed hydroscopic and therefore will always swell whenever it can absorb water. By saying it was unpredictable, my sentence inferred that it would not neccessarily do so, and that is just wrong, so thanks for spotting that.
What I <u>meant</u> was:
The swelling of a nylon part is unpredictable in that swelling can vary significantly depending how stock material is stored as well as for how long it is stored. For example nylon kept for lengthy periods in dry, or, very damp conditions prior to it being machined into a part, will vary the amount of swelling if and when the part is later immersed. What grade the material is made from also plays a role, (nylon 6, 6/6 unfilled, glass filled), and even how it was formed (cast or extruded) affects how it swells.