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Old 19-10-2012, 02:19   #1
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Crevice Corrosion On Rudder Stock

I just pulled the rudder to renew the bearings and boats being boats have found two new problems, one is 5mm deep crevice corrosion at the bottom of the stock for about 2-3 cm the other is the rudder has a slight movement speperate from the stock.

So the rudder ive drilled some exploratory holes and determined the bars that runs from the stock have came loose , so need redone.

The crevice corrosion i am wondering if it is ok, to drill/grin back to bear metal the weld to fill and machine to flat again, or should i replace the stock? time is kinda of the essence as its bloody costly , needing to stay in hotel just now and pay for boat on hard at daily rates..

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Old 19-10-2012, 06:17   #2
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Re: crevice corrosion on rudder stock

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Originally Posted by stevensuf View Post
I just pulled the rudder to renew the bearings and boats being boats have found two new problems, one is 5mm deep crevice corrosion at the bottom of the stock for about 2-3 cm the other is the rudder has a slight movement speperate from the stock.

So the rudder ive drilled some exploratory holes and determined the bars that runs from the stock have came loose , so need redone.

The crevice corrosion i am wondering if it is ok, to drill/grin back to bear metal the weld to fill and machine to flat again, or should i replace the stock? time is kinda of the essence as its bloody costly , needing to stay in hotel just now and pay for boat on hard at daily rates..

oh the joys!!!
it is probably not crevice corrosion,it is more likely to be electrolysis,where the stock exits the hull.

what is the diam of the stock?
welding can distort shafts,though i suspect yours is around 70mm at the base.

loose tabbing is more serious and will need attention,though fairly easy to repair with epoxy and pu foam.
use a fine ss cutting disc to seperate the two halves.
shepards in marina bay should be able to supply materials.

a tip for using 2 pack polyeurathane foam,put comp A and B in the fridge before mixing.
also glassing in the tabs to one side of the rudder moulding will greatly improve the strenght of the repair.
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Old 19-10-2012, 08:32   #3
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Re: crevice corrosion on rudder stock

hi alex, i took the rudder to a local stainless specialist, where we ground out the corroded parts and welded new, made them do it very slowly, keeping it cool.

The movement was caused by the rudder stock and tangs?( 4 rods that come through the stock at 90 degrees angles) coming slightly loose,they are apparently epoxied (not welded) together.

They are now welded, so i now have 4 8cmx8cm holes in the rudder that i need to fill, im thinking chopped strand epoxy mix? maybe remove some of the foam to allow some keying to take place?
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Old 19-10-2012, 08:38   #4
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Re: crevice corrosion on rudder stock

NB funnily enough the corrosion was above the lower rudder bearing, kind of like pitting,some areas fairly deep, the lower rudder section is 65mm the upper 55mm, i had to cut the lower bearing to get it out, however the new one went in very easy, upper was much less worn but replaced as well.

Ach well its all part of the learning curve.
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Old 19-10-2012, 13:07   #5
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Re: crevice corrosion on rudder stock

Quote:
Originally Posted by stevensuf View Post
hi alex, i took the rudder to a local stainless specialist, where we ground out the corroded parts and welded new, made them do it very slowly, keeping it cool.

The movement was caused by the rudder stock and tangs?( 4 rods that come through the stock at 90 degrees angles) coming slightly loose,they are apparently epoxied (not welded) together.

They are now welded, so i now have 4 8cmx8cm holes in the rudder that i need to fill, im thinking chopped strand epoxy mix? maybe remove some of the foam to allow some keying to take place?
filling the voids,you could use epoxy with microfibers mixed in,but this will be quite expensive,a cheaper option would be to use car body filler,or poly resin/micro balloon mix,then epoxy cloth over the top after grinding out a fillet in the surrounding glass on the rudder.
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