rudder shaft bushings

[Fritz Koschmann]

I am building a 40' sailing catamaran with big rudders. The rudders have wooden (purpleheart) gudgeon blocks with a 1" diameter stainless steel rod connecting the rudders to the blocks. The rod has to be bushed where it passes through the rudder flanges, also wood, and the blocks. I was going to use stainless steel tube for the bushing but am having trouble finding stainless tube with the right combination of ID and wall thickness for the required close fit. I suppose it would be possible to have a machine shop machine what ever I need but my pocket book is getting thin. It occured to me that I might use a plastic tubing such as Acetal (delrin) or nylon for bushings. I can get it with a 1/4" wall thickness and a 1" ID, I would have to drill it out slightly to get a good fit. One problem I forsee though is how to fix the delrin tube in place to allow the rod to turn in the tube and not the tube in the rudder flange or gudgeon block. I know I would not be able to glue acetal. Also I don't know how the plastic bushings would work out in the long run, though they might be fairly easy and inexpensive to replace. Any suggestions?

[JimConlin]

I've discovered that there are many styles and sizes of manufactured plastic bearings.
One manufacturer is Igus (http://www.igus.com/)

[sangraal]

One possible low budget, outside the box, and homegrown machinest solution- make thick walled bushings from glass tape and epoxy wrapped on the shafting.of course they'll wear, but its cheap and 'backyard'. If you need the O.D. dimensioned accurately for the bore in your gudgeon blocks you can true them in the drill press-taped with real duct tape-top and bottom on a 1" bit. or other means, with a file or sanding belt etc.A little trial and error and you can find what will work. Or over size the bore in the gudgeon and epoxy the bushings in when you hang the rudders. I'd go with a tight-ish fit of the bushing/gudgeon myself. And make a second set of bushings while your at it. Not sure how your purpleheart blocks are arranged, but i'd be inclined to have straps and bolts reinforcing the cross grain and backing it all up in case of the propabable grain failure in that situation, purpleheart will split.
Having said that, the rudder on any boat is a serious and critical system and no place to be skimpy. Real failures can lead to big trouble. Your 40' cat will obviosly carry big dynamic loads. But you must know that already, building such a project. Personally, I'd save my change until I could get real fittings fab'd by a pro. 316 ss abv the w.l., Sl/Bz below.

[carlg]

I've also discovered IGUS and I think they are available via McMaster Carr.

[Del Lansing]

One problem I forsee though is how to fix the delrin tube in place to allow the rod to turn in the tube and not the tube in the rudder flange or gudgeon block. I think it would rather easy with a titanium drill bit to put a hole in the outer tube and use a roll pin to keep the delrin from spinning/slipping. Or perhaps a short sheet-metal screw if you plan on easy replacement later.
A source of various size delrin stock is US Plastics (http://www.usplastic.com/catalog/product.asp?catalog%5Fname=USPlastic&category%5Fname=8765&product%5Fid=12806)

[David Tabor (sailordave)]

I think it would rather easy with a titanium drill bit to put a hole in the outer tube and use a roll pin to keep the delrin from spinning/slipping. Or perhaps a short sheet-metal screw if you plan on easy replacement later. Exactly what he said!! First thing I thought of when I clicked on this thread.
BUT, if you have the $$$, or even if you almost have the $$$, go first class! ;)