aluminium experts

[tyce]

i am going to remake the rudder stock on my parker 27.
the present one is made of aluminium, does anyone know what grade of aluminium would be suitable for a replacement

 

[FullCircle]

Alubat Ovni make their hulls from Aluminium 5083 T111. Works for them.

 

[oldsaltoz]

G’day Tyce,

You might want to look a bit further, I found this at:

http://www.azom.com/details.asp?ArticleID=2860#_Grades,_Tempers_and


Grade. Comment.
1XXX excellent formability, weldability and corrosion resistance. Low strength.

2XXX Excellent machinable and high strength. Poor formability, weldability and corrosion resistance.

3XXX Formable, corrosion resistant and weldable. Moderate strength.

4XXX Formable, weldable, corrosion resistant

5XXX Formable, weldable, excellent corrosion resistance

7XXX Machinable, poor corrosion resistance and weldability. High strength.

8XXX Excellent formability

I suspect I would be looking for stainless myself, of course we can steer by sail if required.


Avagoodweekend......

 

[cliff]

5083 is usually supplied in flat rolled form (sheet and plate)
5754 is usually supplied as tread plate
6082 is usually supplied as sections
6262 is usually supplied as round bar and is used in marine fittings including hinge pins

If I was making a new rudder stock I would go for stainless steel as first choice but if I had to use Aluminium I think I would go for 6262.

Your boat, your choice but I would go for at least a 5XXX series if not the 6XXX types. (Stainless steel as first choice though)
--------------------

"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[kengill]

whatever you do don't use a 7XXX series alloy

Iif you clean a section and lightly press a clean dry finger to the surface you can read the fingerprint the next morning which has been etched into the surface.

 

[Ships_Cat]

That is not quite correct. 7075 is used quite often for situations where weight is important eg race boats, due to its higher strength. Therefore it is important to make sure that an existing stock being replaced is not 7075 because if the existing stock is 7075 and one replaces it with another alloy then one will end up with an understrength shaft.

However, 7075 is not so corrosion resistant in seawater so may be anodised and at least regulalrly inspected. The important thing is that if ones existing stock is 7075 then one must stay with it in order to maintain strength.

6082 is the alloy normally used for rudder stocks.

SS has been mentioned - while its tensile strength and elastic modulus is higher than aluminium it will permanently deform under lower loads than aluminium of similar dia - therefore it also should not be used instead of aluminium if the original stock is aluminium. Due to aluminium's lower elastic modulus it will deflect under load (but not permanently deform) more than ss so if using an aluminium stock one should be sure that the bearing arrangements account for this (often self aligning) - one assumes that the original poster's bearing arrangement is fine in that were built for an aluminium stock.

Out of all that the original poster would seem advised to replace with aluminium, probably 6082 but should ensure that a higher grade alloy was not used in the original build eg 7075 (I am not familiar with the actual boat) else will end up with an understrength stock. Would also be unwise to substitute ss as if the current design is operating over the proof load of ss (that being lower than for aluminium) may end up with a bent rudder stock.

(Most of the above comes from a sad experience where for a new build large yacht with aluminium stock and going into class had its stock underdesigned - was not discovered until hull and rudder were built /forums/images/graemlins/frown.gif)

John

 

[tyce]

thankyou all, as usual very helpful replys looks like 6082 is the best bet