Rudder top bearings

[4HMainer]

Make sure your bearing has enough of a clearance on the shaft, you need to allow for moisture absorption as well as thermal expansion and add these to the minimum running clearance. If it's too tight it will get tighter with heat and friction.

[coopec43]

Originally Posted by 4HMainer

Make sure your bearing has enough of a clearance on the shaft, you need to allow for moisture absorption as well as thermal expansion and add these to the minimum running clearance. If it's too tight it will get tighter with heat and friction.

There shouldn't be any water absorption if it is proper bearing material.

https://www.cruisersforum.com/forums...p/t-81297.html

[4HMainer]

Sorry Coopec but all current composite and plastic materials used as bearings absorb moisture. Some less than others but all of them do. Unless you are talking about metal bearings you need an allowance for moisture expansion. In typical advanced composite material with the lowest moisture absorption (less than delrin or UHMWPE) for a 2" x 2.5" running clearance is 0.05mm allowance for moisture swell is 0.04mm and for thermal expansion unplanned 0.06mm. So 0.15 is considered min clearance. When we know a system will be constant temperature then we can ignore thermal expansion and run smaller clearances.

[4HMainer]

Actually Coopec you're lucky as the best marine bearing materials are made in Perth WA. Look for Maritex.

[coopec43]

Originally Posted by 4HMainer

Sorry Coopec but all current composite and plastic materials used as bearings absorb moisture. Some less than others but all of them do. Unless you are talking about metal bearings you need an allowance for moisture expansion. In typical advanced composite material with the lowest moisture absorption (less than delrin or UHMWPE) for a 2" x 2.5" running clearance is 0.05mm allowance for moisture swell is 0.04mm and for thermal expansion unplanned 0.06mm. So 0.15 is considered min clearance. When we know a system will be constant temperature then we can ignore thermal expansion and run smaller clearances.

So you are saying "0.15 is considered min". Is that 0.15mm allowance on a 2 inch shaft?

I've had this argument before (on a different forum). When I installed the rudder on the yacht I am building I had advice from the experts and I can assure you the tolerances were not so critical that you had to consider 0.15% water absorption.

[coopec43]

Monday, January 14, 2013

Surveyor Guide Notes for Rudder, Rudder Stock and Pintle Survey


https://marinesurveypractice.blogspo...le-survey.html

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[4HMainer]

Yes I used a bearing with ID 50.80 x OD 63.5 as an example. The wall thickness also has an impact on running clearances.



If you want a bearing to have a long life you want it to start at it's minimum clearance, so why not consider all the variables. The example you gave shows a 1.00mm clearance which is 6 x what's needed for a bearing material with low thermal and low moisture swell. As thermal and moisture swell is a percentage, the wall thickness of the bearing should be taken into account. We calculate the clearance for each bearing. We end up with bearings lasting a long time.It's what I do for a living although we now mostly supply bearings for critical pumps where smaller clearances mean greater efficiency, but we started in Lloyds marine bearings.

[Searles]

If that stock is alu or sim keep all copper anti fouling paint at least 12inches away in all directions ,just hope it’s s s .😇⚓️

[vladkri]

Thanks everyone for the input. The material I used is Delrin and the stock is aluminum. Due to grinding for many years before, the stock now has some shaved area and a bit of play. I used silicone lube and covered previously exposed top to prevent dirt coming into the top bushing. Seems fine at the end of the season.

[coopec43]

Originally Posted by vladkri

Thanks everyone for the input. The material I used is Delrin and the stock is aluminum. Due to grinding for many years before, the stock now has some shaved area and a bit of play. I used silicone lube and covered previously exposed top to prevent dirt coming into the top bushing. Seems fine at the end of the season.

Nice to get that feedback