Stainless rudder

[Croak]

Fiberglass rudder has departed from the stock.

What are the problems with welding a stainless plate, the same dimensions of the rudder onto the stock?

 

[TQA]

Heavier.

Getting some tangs welded on and making a new one from foam and glass is not a big deal.

 

[dt4134]

Stainless steel will still corrode underwater so you will need an anode for it.

 

[wklein]

I imagine you would struggle to get any antifoul to stick to it.

 

[Fire99]

I Have a Galvanised blade on my stock (as opposed to wood, I do believe) and it's bleedin' heavy.

Antifouling isn't a big issue if you use something like Primocon first.

 

[Croak]

Stainless steel will still corrode underwater so you will need an anode for it.

The rudder stock is stainless so does this not corrode under water? or need an anode?

The boat is on a drying mooring.

 

[Croak]

What are the problems with it being heavier.

Would the bearings not take the extra weight?

 

[Tranona]

Would have to be quite thick, at least 6mm, possibly 8mm to be stable enough - therefore very heavy, and flat plates are not efficient. If it is 316 should not have corrosion problems except possibly at the welds. Probably lots of beer tokens to get ss plate of that size cut to shape.

However, as suggested, much easier to have tangs welded on and build up a proper shaped rudder out of ply or foam sheathed with glass/ epoxy.

 

[wklein]

They often make rudders buoyant to lighten the steering, so i imagine that the opposite would be true.

What do steel boats do? Last one i sailed on definitely had a buoyant rudder as it kept banging the hull every time it pitched.

 

[Croak]

Would have to be quite thick, at least 6mm, possibly 8mm to be stable enough - therefore very heavy, and flat plates are not efficient. If it is 316 should not have corrosion problems except possibly at the welds. Probably lots of beer tokens to get ss plate of that size cut to shape.

However, as suggested, much easier to have tangs welded on and build up a proper shaped rudder out of ply or foam sheathed with glass/ epoxy.

Not me, the man in question is no stranger to stainless but is a stranger to fibreglass.

 

[Tranona]

Not me, the man in question is no stranger to stainless but is a stranger to fibreglass.

Suggest he asks himself when he last saw a stainless plate rudder, except on a high speed planing boat? Nothing difficult about building a proper rudder - in fact the most difficult bit is welding the tangs on so that they are at right angles to the pivot point and straight.

I am assuming this is a sailing boat where a foil is required - plate rudders are common on motor boats where they just deflect the water flow from the props.

 

[Croak]

Both of my cats' had plate rudders.

 

[Oldhairy]

What are the problems with it being heavier.

Would the bearings not take the extra weight?

Might cause lee helm and can cause the rudder to take the weight of the boat when aground.

 

[rogerthebodger]

I have a steel boat and my rudder is steel as well with a stainless steel stock

Ribs the shape of the rudder profile were welded to the stock that went all through the rudder and then 3 mm steel plated welded to the stock and together at the trailing edge. Holes were cut through the side plated to allow the side plates to be welded to the ribs.

A hollow rudder like this in fact is too light on water so I filled mine with old engine oil to weight it down and protect the inside from corrosion, this will not be needed if made of stainless which should be 316 to prevent corrosion.

Have a look at this site

http://www.boatdesign.net/forums/boat-design/stailess-steel-rudder-27641.html

and

http://metalboatbuilding.org/phpBB3/viewtopic.php?f=22&t=776

 

[PCUK]

My steel boat also had stainless stock and steel rudder. No problems in 26 years!

 

[John the kiwi]

Keel and rudder design

A flat plate rudder is a bad idea unless you have excess horsepower such as on a power boat. This article explains lots of stuff.

http://www.sponbergyachtdesign.com/Keel and Rudder Design.pdf

Stainless Steel requires to be in an oxygen rich environment to maintain the chrome oxide surface layer that in fact makes it stainless. Therefore stainless is generally not recommended for continuously immersed applications where oxygen is lacking.
However, shallow water is oxygenated to some degree and stainless propellors etc seem to last ok fully submersed.
I have often wonder about making a hollow stainless steel rudder by wrapping say a 2 mm thick sheet of ss around a set of ribs to form a NACA 0012 profile.
Given a suitable press brake you would only need to weld a single seam down the training edge plus a few spot welds to the ribs. Ok it would be a straight parallel sided section, but this could work.
If you do try it, would love to know the result.
Cheers

 

[Croak]

A flat plate rudder is a bad idea unless you have excess horsepower such as on a power boat. This article explains lots of stuff.

http://www.sponbergyachtdesign.com/Keel and Rudder Design.pdf

Stainless Steel requires to be in an oxygen rich environment to maintain the chrome oxide surface layer that in fact makes it stainless. Therefore stainless is generally not recommended for continuously immersed applications where oxygen is lacking.
However, shallow water is oxygenated to some degree and stainless propellors etc seem to last ok fully submersed.
I have often wonder about making a hollow stainless steel rudder by wrapping say a 2 mm thick sheet of ss around a set of ribs to form a NACA 0012 profile.
Given a suitable press brake you would only need to weld a single seam down the training edge plus a few spot welds to the ribs. Ok it would be a straight parallel sided section, but this could work.
If you do try it, would love to know the result.
Cheers

I can't see a comparison between a foil and a flat plate in that link.

It also seems that the performance losses are much greater at higher speed. As this is a 24 foot yacht, I can't see that a great deal of performance will be lost at 4-5 knots

 

[DownWest]

I am just waiting on sizes to build a SS rudder for a small powerboat. Stock is 25mm solid and the foil will be 2mm bent round in an aproximation of a NACA section. The boat will be mostly used in fresh water so corrosion is not really a problem. 316L will be the material. If a larger one for a sailing boat, then ribs, as above.

 

[grafozz]

no it wont ,

Stainless steel will still corrode underwater so you will need an anode for it.

I have stainless rudders and they are many years old and perfect .no anodes required

 

[John the kiwi]

Sorry i misremembered about flat rudder vs profile rudder in the article.
I thought it a very interesting read even though i suspect the author would simply curl his lip and sneer at the very idea of a flat plate rudder on a yacht!
Nonetheless, the turbulent drag from a flat blade rudder could cost you significant and measurable speed. The difference between 5 knots and 4 knots is an extra hour over a twenty mile passage. If your boat is already not a fast boat why would you want to handicap it further? i would be looking to make the most efficient rudder i could.
Just my opinion and the one of the great things about owning your own boat is being able to do with it as you please regardless of the opinions of others.
Good luck