[Public-List] corroded rudder

[Michael Connolly]

Stephen,
George pointed out what I was going to tell you.  What you posted was only the first of two pages.  The photos in your second recent post clearly illustrate what I was suggesting. That is the rudder stock, i.e., the piece that the tiller head is attached to is indeed 1' in Dia. and NOT continuous as you have shown in your drawing over your photograph.  One piece of the stock at the top goes down to the lower corner of the bottom of the prop aperature and ends there. The second piece is also 1" in Dia. and is 9' long and is the piece at the lower front edge on the blade. This is the piece which has the 1/2" pin which fits into the rudder shoe.  The thrid piece which is shown as George pointed out is 3/4" Dia.  IT IS SEPARATE from the other two and is of a smaller diameter.  It is NOT part of the rudder stock but is actually the middle gudgeon pivot pin. -You do not have two gudgeon with a floating pin as do some boats.  What you have is a split (or two part) gudgeon fitted to the dead wood of the aft keel, and then a pivot pin securely encapsulated in the leading edge of the blade forming the middle hinge of the rudder blade.
This pin is not 1' in Dia but originally 3/4" so you have 64% of the original strength as you have calculated.

I hope I have now made it clear to you. I have tried to suggest that you not make this project more involved than it needs to be. Granted that the middle pivot might be only 64% of the original in diameter.  The boats are over built. 5/8" of pivot pin at that juncture is plenty enough.  I have stated that if when you clean up the corroded pin you can not get down to any brass like appearance then the entire pin might be dezincafied and thus severely weakened.  If you polish the pin and can get to a nice brass finish and color then you still have good metal there. 

If in your case you wish to replace that pin it is EASY for you to do.  Excavate above and below your pivot pin along the leading edge of the blade, just enough to come to the end of the metal. The entire 3/4" pin is only 5" long. You only have to excavate 5" along the leading edge of your rudder.................thats all.  Remove the old pin and replace it with a new piece. If the gudgeon is worn and you use a 3/4" new pivot then you will likely have to make a bushing to make up the difference in diameters. 

If I were doing this I would use a bronze pin and Derilin(r) bushing. If you are replacing the pin you can slip the bushing on before you embed the pin into the blade.

As I mentioned before if the actual rudder stock, upper and lower, are secure then leave them alone.  You can easily replace the middle pivot pin and drill out the lower rudder stock to replace the lower 1/2" pivot WITHOUT removal of the rudder from the boat. 

What other issues do you see with the blade itself?  Fractures, weakness, delamination or water saturation?  If nothing then don't make more work for yourself.
Best,
Michael #133
> On 03/16/2021 3:08 PM George Dinwiddie via Public-List <public-list at lists.alberg30.org> wrote:
> 
>  
> Stephen,
> 
> On 3/15/21 12:17 PM, Stephen Gwyn via Public-List wrote:
> > Michael Connolly:
> > So if the diameter of the shaft was originally 1", and it's only 0.6" 
> > now, then the cross section is 0.6 squared = 0.36 of
> > the original, hence my figure of 36%. If instead the original diameter 
> > was only 3/4" inches, then the remaining strength is
> > (.6/.75)^2  = 64%, still not great, but much more acceptable. However 
> > all the bits of brass I can see are 1", which
> > is also the diameter specified here:
> > http://www.alberg30.org/maintenance/Steering/RudderPost/rudderstock.png
> 
> That page shows the upper post that attaches to the tiller.
> Note the piece in the lower left corner of the second page, 
> http://www.alberg30.org/maintenance/Steering/RudderPost/RudderReinforcment.png
> 
>   - George
> 
> -- 
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