Another Hunter Rudder!

[pbiJim]

Originally Posted by hellosailor

Dan, it is common when bending thin copper tubing (icemaker water lines, etc.) to fill them with sand if you don't have a bending spring, before bending them.

I normally use a low melting point alloy called Cerrobend. It's pretty convenient to work with as long as you remember to quench it before it solidifies.

[neilpride]

Originally Posted by hellosailor

Dan, it is common when bending thin copper tubing (icemaker water lines, etc.) to fill them with sand if you don't have a bending spring, before bending them. The sand prevents them from collapsing on the bend. So filling a tube DOES work, but everything depends on the relative merits of the tubing wall and the filling material. If you had an unlimited budget and really wanted to max out the rudder post, you could insert multiple tubes inside of it, snugly, and "honeycomb" the rudder post making it almost as strong as a solid rod but at greatly decreased weight. And of course increased cost.

Bronze got a bad name when the "miracle" of stainless steel cookware and knives was sold to the world in the (50s?). Tell a boat buyer you are using bronze parts, bronze structural parts, and you'll frighten them away. Bronze, that's like, something that came in between the stone age and the iron age, right? No sale. Forget the price, no sale.

Not quite true, my rudder stock is made of naval bronze, 2 inch and half solid, is 35 years old, the rudder is droped from the boat now, the shaft , rudder stufing box, quadrant, and heel plate are solid bronze , no pitting, pink color, or damage, not even the small trace of corrosion, is a hell of rudder... droped because i cant paint well the skeg inside and top , but i get the chance to inspect the shaft , clean it, and repack the stufing box . 35 years old!!! i wonder if a hollow fill it alu or ss can last this years..

But you are right about how expensive is bronze for a rudder... Now SS take the place...

[pbiJim]

Originally Posted by Rakuflames

It's high quality stainless steel. I forget the number -- don't have the background knowledge on the different types.

If you can dig up the number, I can probably find some information on it.

A lot of the "good" stainless alloys can actually become fairly brittle from prolonged fatigue. I've seen this first hand on 316 shafts well over a foot thick in industrial applications.

[neilpride]

Is quite a good idea in case of rudder refit to use Aquamet or better Nitronic 50, Aquamet is used in prop shafting and have better corrosion resistance than 316 or 304, even the torsional strenght is far better, Nitronic 50 ? never hear something like Nit 50 used for rudder stock, but worth to ask, corrosion resistance is also in the `+side...

[pbiJim]

Originally Posted by neilpride

Thx for the info, i just believe CF is lighter and stronger than regular FG and even in some cases stronger than SS, repairs can be made in the same fashion as normal Fg , but anyway i dont know the circunstances or the reason why this 2 Cf rudders fail.

I've worked with CF shafts. I've worked with stainless shafts. I've worked with hybrid CF/stainless shafts. I've worked with hybrid CF/aluminum shafts.

Carbon fiber is strong & lite weight, but it wears more easily than many other materials, it doesn't do repeated elastic deformation very well & it generates a lot of abrasive when it deteriorates. I have not yet had good luck repairing CF. Perhaps others have.

CF is not my first choice of material where I want something to last a long time. It is however, a great material for short-lived race vehicles of many descriptions.

Hybrids of CF tend to give better long range performance when properly designed & constructed, but creating those marvelous hybrids is generally not an inexpensive 5-minute task.

[neilpride]

Originally Posted by pbiJim

I've worked with CF shafts. I've worked with stainless shafts. I've worked with hybrid CF/stainless shafts. I've worked with hybrid CF/aluminum shafts.

Carbon fiber is strong & lite weight, but it wears more easily than many other materials, it doesn't do repeated elastic deformation very well & it generates a lot of abrasive when it deteriorates. I have not yet had good luck repairing CF. Perhaps others have.

CF is not my first choice of material where I want something to last a long time. It is however, a great material for short-lived race vehicles of many descriptions.

Hybrids of CF tend to give better long range performance when properly designed & constructed, but creating those marvelous hybrids is generally not an inexpensive 5-minute task.

But where is the wear?? at the bearing races? sorry if i ask , i see some stocks made of Fg and at the bearings point there is a metal bushing atached to the stock, all the wear is there? or i miss something, cheers....

[pbiJim]

Originally Posted by transmitterdan

I think if you do a finite element analysis of the tube you will find it is not much stronger when filled with something. The side loading forces on the the shaft cause tension on one side of the tube and compression on the other side. The tension stresses are not much affected by the filling material.

Your point is perfectly valid in some circumstances & invalid in others. Generally speaking, hollow round metal tubes are much stronger than solid shafts of the same material & weight, when evenly loaded. The addition of a concentration factor, like a fulcrum, changes everything.

[pbiJim]

Originally Posted by neilpride

But where is the wear?? at the bearing races? sorry if i ask , i see some stocks made of Fg and at the bearings point there is a metal bushing atached to the stock, all the wear is there? or i miss something, cheers....

The bearing point would be the area most likely to see the fastest & heaviest wear. A metal ring fitted firmly to that area of the CF would be an example of the hybrid shaft that I spoke of. The hybrid joint itself is an area of potential wear, but hopefully takes much longer to give out than the bare CF would. There may also be internal stress-related wear, but that generally takes even longer to materialize, unless the CF was under built for the application. I don't think that you missed much.

[pbiJim]

Originally Posted by psneeld

Has anyone addressed crevice crack corrosion on the stainless shafts for these rudders?

I'm not real well versed on that subject. Can someone point me to a good place where I can read up on it? I'd like to learn a little more about that possibility.

Thanks,
Jim

[robert sailor]

Nothing will steer a boat as well as a spade rudder however spade rudders have a poor reputation offshore primarily because most of them are under built for continued offshore sailing.
It costs quite a bit more money to build a bullet proof spade rudder but they are certainly out there, have a look at some of Dashew's rudders.
They are not built by Hunter or Beneteau or Bavaria or any other mass produced builder.

[pbiJim]

A couple of months ago, I went to look at a Hunter that was for sale down in the keys. I think that one was a 27. It had a bent rudder post. That was only one of the reasons why I passed on the opportunity to buy it, but hearing about these other rudder problems makes me think that I probably need to learn more about this possibly-common flaw if I am going to continue to keep Hunters on my may-buy list. This thread has been very educational for me.

Thanks Guys

[neilpride]

Zincs!! come to my mind and avoid tricky marinas...and well if you have a bad + leak onboard , a couple of friends in a wauquiez found the rudder stock with just mm left of metal holding the rudder in a haulout, the culprit? a positive wire rubbing with the stainless steel wires cables inside of the pedestal, to late for the rudder, but at least the couple found the problem with the boat out of the water.. after dismantle almost all the elctrical system onboard lol..

[fgd3]

Originally Posted by hellosailor

"A hollow shaft is weaker than a filled shaft,"

A hollow shaft is weaker than a filled shaft, all other things being equal.

Originally Posted by hellosailor

Only marginally. This is why spinnaker poles, masts, booms, structural support columns in buildings, are all unfilled columns, not solid posts.

All of those examples are used to support compression loads, not side loads. A rudder shaft is quite different.

Originally Posted by hellosailor

Unless your "filling" is quite substantial, it contributes very little. Even when it is quite substantial, it doesn't add much compared to a slight increase in column wall thickness.

If you increase the wall thickness all other things are not equal.

Originally Posted by hellosailor

A typical rudder post is supported internally in the rudder tube, and then externally inside the rudder itself. There is really very little rudder post exposed in between the hull and the rudder, which could be subject to buckling from side loads. It is fairly simple to make the post stronger than the hull or rudder which are attached to it.

And again, if the post is stainless steel? Doesn't matter if it is filled or not, it can still fail from crevice corrosion. Stainless is the wrong metal for this application.

The question wasn't how to build the best possible rudder shaft, it was why did the manufacturer fill the shaft with foam? The answer is he was trying to get a little more strength from the thin-walled tubing he chose.

There's no doubt different design choices would have resulted in a more robust rudder shaft.

Fabbian

[neilpride]

Thin wall filled with foam sugest me Builder saving costs at the owner risk...

[fgd3]

Originally Posted by robert sailor

Nothing will steer a boat as well as a spade rudder however spade rudders have a poor reputation offshore primarily because most of them are under built for continued offshore sailing.
It costs quite a bit more money to build a bullet proof spade rudder but they are certainly out there, have a look at some of Dashew's rudders.
They are not built by Hunter or Beneteau or Bavaria or any other mass produced builder.

I wish you would expand on your assertion that nothing will steer a boat as well as a spade rudder. It seems to me that a transom-hung outboard rudder will steer a boat better than a spade rudder. The outboard rudder can be a little smaller because it is farther from the boat's center of rotation, so it can produce the same torque with less lift. I thought the preference for spade rudders was that the rudder mounting could be made stronger than pintles and gudgeons on the transom. Can you elaborate?

Fabbian