What about a stainless steel rudder?

[Cspirit]

I have a Westerly Corsair with the usual rudder arrangement - stainless shaft/web with a GRP cover. I've been told by another Corsair owner that he has replaced his rudder with a stainless version - same dimensions etc. Apart from costs, can anyone think of a reason not to do this, rather than removing and renovating the existing rudder?

 

[janeh]

stainless is not designed for permanent underwater situations.

it needs oxygen to work as it is supposed to, but lots of people still do use it underwater permanently

 

[Phoenix of Hamble]

What is the weight difference between the two?

I would have thought that an all stainless rudder would be excrutiatingly heavy... probably sufficiently so that it would upset boat balance when hung right at the stern....

 

[VicS]

[ QUOTE ]
it needs oxygen to work as it is supposed to

[/ QUOTE ] A rudder blade is in well oxygenated water surely. The bit most at risk, from crevice corrosion at least, would be the shaft where it passes through the bearing bushes.

Would like to take advice from a metallurgist familiar with the use of stainless steel in the marine environment especially regarding the welds that would be necessary.

 

[janeh]

Yes, especially turbulent water - perhaps this is why the metal rarely fails in these conditions.

Have welded stainless; both mig and arc. You have to match the quality of the metal being welded with the rods or wire. And choose the right gas with mig.

Welds must be as smooth as poss and polished well afterwards to limit crevice corrosion, as you mention.

Have no info on strength of welds though.

Welding in aluminium however does weaken the overall structure (in local vicinity) by an amazing 50%.

 

[Twister_Ken]

Weight in the end of the boat. Apart from the trim effects it would increase pitching considerably. Look up 'polar moments of inertia'.

 

[Blueboatman]

If you were to build a hollow metal rudder you will have to add weight internally to counter its buoyant tendency to fight you at the helm as it tries to twist about the shaft and 'float' to the surface,which would make the helm feel distinctly weird if it were attached to a free moving tiller,for example.. For this reason rudders tend to be solid and heavy (neutral buoyancy).
I would think that where the stainless is welded you may have problems but, hey, try it and report back ?

 

[NormanS]

Quote:- "If you were to build a hollow metal rudder you will have to add weight internally to counter its buoyant tendency to fight you at the helm as it tries to twist about the shaft and 'float' to the surface,which would make the helm feel distinctly weird".
That's a really strange idea,-- wood (which floats) has been used for making rudders for centuries.

 

[BAtoo]

If a stainless steel rudder was a good idea we would all have one..........










And Westerly would have gone under sooner..........











And if they were all going to corrode and fall off you would not be asking this question...... /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

 

[Otter]

[ QUOTE ]
Quote:- "If you were to build a hollow metal rudder you will have to add weight internally to counter its buoyant tendency to fight you at the helm as it tries to twist about the shaft and 'float' to the surface,which would make the helm feel distinctly weird".
That's a really strange idea,-- wood (which floats) has been used for making rudders for centuries.

[/ QUOTE ] Wood is massively less buoyant than air.

 

[NormanS]

Quote:

"Wood is massively less buoyant than air.)

Yes, and stainless steel is massively less buoyant than wood. You would have to build a very fat hollow stainless steel rudder, before it would float. Do the maths!

 

[oldsaltoz]

web page

 

[Bajansailor]

Almost all of the commercial fishing boats here have flat plate S/S rudders, and they do seem to work very well - many are over 20 years old, and do not appear to have suffered from crevice or any other types of corrosion.
The owners are invariably assiduous about protecting them with zinc anodes though.

Here is a photo of a typical rudder on a timber fishing vessel :

 

[damo]

Rudder heels and skegs are often stainless, the shaft is stainless, your anode bolts are stainless, your prop shaft is probably stainless, so where do you get the idea that it is not for underwater use??

It is the exclusion of oxygen that leads to crevice corrosion, so as Vic said the shafts are far more vulnerable.

A mate made his windvane rudder from thin stainless plate - hollow with internal webbing. Sure it's a bit heavier, but then there are no problems with water getting into the grp/shaft area and causing, ahem, crevice corrosion and the loosening that is very common on the usual rudder construction.

For the OP, I am surprised that it isn't the standard method of construction.