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S&S Swan Maintenance - Nyloc or a locking double nut?
09 April 2016 - 22:19
#1
Join Date: 01 February 2007
Posts: 234

Nyloc or a locking double nut?

I recently read an article ref the Oyster 82 that lost its keel and thought the idea of securing a locking nut on the keel bolts sensible, as this stops the lower nuts from creeping.

However the question I am seeking an answer too is what is the best approach to the problem of creep in nuts.  I have recently launched my 411. After using a torque wrench on the keel nuts they all had some further tightneing to achive the recomended torque setting. Have removed the keel some years back the nuts must have worked loose slightly over time.

From an engineering point of view is it better to use (a) Nylocs  (b) a second locking nut 

10 April 2016 - 19:59
#2
Join Date: 02 January 2008
Posts: 1547

Dear John

The recommendation is to use Nyloc, this is a straightforward way. Pls note that the torque should be increased slightly because there is increased friction in the nut locking ring. Ask the supplier how big the prevailing nut torque is, and add this to the prescribed torque.
Two nuts require more thread length, and special procedures to achieve proper locking and pretension.
You say that the nuts worked loose slightly over time, I would suggest that this was the result of a slow creep in the GRP when in constant compression. 
Kind regards
Lars

11 April 2016 - 09:08
#3
Join Date: 02 February 2007
Posts: 200

Hello John and Professor.

Should not these nuts be also carefully be glassed over to avoid any intrusion of salt water and subsequent risk of oxygen deprived corrosion???

I also read the story of the oyster keel disaster in YW. It was really an horrific construction. But this is not the place to discuss it!

Kind regards.

Philippe 41/022

13 April 2016 - 09:48
#4
Join Date: 02 January 2008
Posts: 1547

Dear Philippe


Would suggest that crevice corrosion to stainless caused by oxygen starvation may be avoided in two alternative ways - either encapsulate the keel bolts completely, so water can not reach their surface, or leave them open, allowing the bilge water to carry around oxygen.
An intermediate solution, i.e. leaking encapsulation, is likely to be the worst solution.
 
Before encapsulating the bolts it must be made absolutely sure that there are no leaks around the bolts from the outside, because there will then be no signs of this on the inside. 
Kind regards
Lars

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