Rudder Advice please

[paul_jarrett]

I'm rebuilding a project, Macwester Rowan, the pin on the keel (long keel) which was tufnol had broken so i've manufactured a stainless one, the question is, the rudder was sleeved with fibreglass am i ok to buy ptfe sheet and roll it into a tube and epoxy it in to replace or will the ptfe swell like nylon, if so anyone know where to get grp tube?

Thaks
Paul

 

[Bilgediver]

I'm rebuilding a project, Macwester Rowan, the pin on the keel (long keel) which was tufnol had broken so i've manufactured a stainless one, the question is, the rudder was sleeved with fibreglass am i ok to buy ptfe sheet and roll it into a tube and epoxy it in to replace or will the ptfe swell like nylon, if so anyone know where to get grp tube?

Thaks
Paul

If you have changed the pin to stainless then why not make a Tufnol bush.

 

[BERT T]

PTFE

Yes PTFE will swell when in water, what diameter is the pin?

 

[Iain C]

Acetal rod, suitably machined is good too, won't swell and a lot cheaper than tufnol.

 

[oldharry]

Yes PTFE will swell when in water, what diameter is the pin?

PTFE does not swell at all. Thats why my boat has it for rudder bearings (though hull). How ever it does wear more quickly than tufnol. Nylon can jam up within months.

Edit, would not use PTFE if (when?) I was doing it again, its just a bit too soft.

 

[Neil_Y]

The problem with PTFE is that it is a soft maliable material and it deforms under load but it does not absorb water at all. However as it is soft it suffers from creep the surface layer is dragged and the material deforms, which explains it;s higher wear rates. We use MoS2 and graphite, MoS2 has lower dry friction than PTFE but it is hard in a phenolic resin matrix and doesn't suffer from creep.
PTFE also has a huge thermal expansion so when there is temperature change you need to rund large clearances.

There are a number of composites that are marketed as bearing materials but the actual performance varies quite a bit depending on lubricant/load/temperature/sliding surface material and duty cycle. Tufnol, peek, Orkot, Thordon, vesconite, vespel are examples, however they all suffer from moisture and thermal swell to a degree and this needs to be understood.

Delrin is OK but also softens with heat/friction and deforms under load, but takes a lot more load than PTFE. It does absorb moisture so an allowance needs to be added in the running clearance, it also swells with heat so an additional clearance is needed especially if it is likely to see more than 20C.

Nylon is not good in water as it has quite high moisture absorption.

The latest materials (past 20 years) are composites based on phenolics (so hard) but with ingredients which give low friction when running dry and low or no shaft wear (tested at 20Mpa). These top end materials have answered many of the draw backs of other composites and plastics but they are not cheap.

 

[CreakyDecks]

Delrin is dirt cheap on Ebay.

 

[paul_jarrett]

Thanks for all the answers, I'll have a look how much wall thickness i can accomodate, its not much as the pin is 25mm, i think the old grp was around a 1mm wall

Paul