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Old 19-03-2014, 17:56   #16
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Re: Make a new rudder

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Originally Posted by ilCigno View Post
I would very much recommend to read the information from a specialist on rudders, rudderstocks and materials first.
Thank you. That's very helpful information.
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Old 20-03-2014, 01:19   #17
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Re: Make a new rudder

You might well consider using 2205 duplex stainless rather than any of the 300 series. It is significantly stronger and stiffer and far less susceptible to crevice corrosion. It has been reported here on CF that it is not much dearer than 316, but I have not purchased any lately.

Cheers,

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Old 20-03-2014, 03:30   #18
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Re: Make a new rudder

i have a friend who had his made of monel. A welder who worked offshore oil rigs put it together for him. He has the option of filling it with oil. Sounds like the ultimate rudder to me.
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Old 20-03-2014, 05:10   #19
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Re: Make a new rudder

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Originally Posted by Sailorman Ed View Post
Along the same lines, my "new" boat has a bent SB rudder shaft when picked up by misplaced sling during Sandy. Looks bent backward about 10-15 degrees. PO just removed a little at the top of the rudder where it was hitting the hull. I would have to dig a 30" deep hole to drop the rudder. Not sure what the shaft is yet, assume SS but if so, can it be straightened? Is 10-15 degrees worth worrying about? (you can see the difference between the boot stripe and the bottom of the rudder)
Ed
30" ???

I had to go 5-1/5'... Twice... with MacGyvered bilge pumps in the hole...
Are you complaining ya nancy?

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Originally Posted by hellosailor View Post
Stainless will just bend, "but"...

The problem is that a stainless rudder post will always be subject to crevice corrosion since there is anoxic (still) water inside the rudder itself. Doesn't matter how you seal the post where it enters the rudder, water will get past that seal.

Completely disagree.... water will not "always" get in... Does it??? = quite often yes...

Once this has happened, the crevice corrosion can lead to a sudden and complete rudder post failure, just as sudden as any composite failure. And the beauty of this failure mode is that it is guaranteed to happen. The only question is, five years? Or forty? At some point, it is going to happen and the only question is when.

So if you plan to get rid of the boat in five years, no worry, use stainless. If you plan to keep it for 20 years, pay very good attention to the seal on the rudder post and inspect your rudder to see if it has gotten waterlogged. All in all...I can't help but think that an excessively strong composite shaft will "never" break in normal use. As opposed to stainless, which is laying in wait, conspiring at the molecular level, just sulking down there and waiting for the Least Convenient Moment.

I have no idea what, say, a two inch thick graphite and kevlar composite rod (not tube) stock might cost. But hey, that's accounting not engineering. There's always a 7-11 you can rob, right?
I suggest that a composite shaft and associated framing is beyond the skill set of the average sailor... Just my opinion...
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Old 20-03-2014, 05:45   #20
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Re: Make a new rudder

What about using a duplex SST like 904L? There was a recent thread on CF about making chain plates from something other than 316.
If you use SST, definitely 316L. The "L" means low carbon, which is useful when welding.
Regarding fabricating the rudder: I have seen an expanding epoxy foam product that I believe is sold by WEST. It's expensive but as I recall was a very good choice for rudders as it will not hold any water. Anyone know more about this?
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Old 20-03-2014, 06:05   #21
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Re: Make a new rudder

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Originally Posted by Dale Hedtke View Post
What about using a duplex SST like 904L? There was a recent thread on CF about making chain plates from something other than 316.
If you use SST, definitely 316L. The "L" means low carbon, which is useful when welding.
Regarding fabricating the rudder: I have seen an expanding epoxy foam product that I believe is sold by WEST. It's expensive but as I recall was a very good choice for rudders as it will not hold any water. Anyone know more about this?
Dale... I think the duplex you are referring to in the recent discussion is the 2xxx series as Jim states below...

Foam can be bought at US Composites in Nicholson58's link... But I suggest his use of the micro balloons and epoxy are superior...

This however brings up a different point to ponder regarding a blade rudder... If you build it strong enough with the full epoxy resin/filler/bullet proof skin... Do you want a sacrificial blade end that will leave you maneuverable should you hit something hard??? If it's stout as a house, the likelihood of bending a shaft and jamming a rudder increase...

Pros and cons with both approaches!!!

PS: I lean toward the sacrificial camp... and OBTW... skeg hung rudders are not applicable to this dilemma.....

Quote:
Originally Posted by Jim Cate View Post
You might well consider using 2205 duplex stainless rather than any of the 300 series. It is significantly stronger and stiffer and far less susceptible to crevice corrosion. It has been reported here on CF that it is not much dearer than 316, but I have not purchased any lately.

Cheers,

Jim
Quote:
Originally Posted by Nicholson58 View Post
Ours is 1984. The post is solid 4" diameter SS with 3 ribs welded on. The overall length is about 10 feet. We dug the hole in the ground to remove and to put it back. The hole is easy. (use a mattock) No bends but total delamination. We rebuilt on the same SS using US Composites 635 Thin resin. Fiberglass , Epoxy , Composites, Carbon Fiber - U.S. Composites, Inc. For filler, I compounded the 635 resin with microballoons. 10 gallons of balloons with 3 gallons of epoxy yields about 13 to 14 gallons of syntactic foam. It is 3000 psi compressive strength and totally waterproof for ever. I skinned the rudder with vacuum bagged carbon fiber.
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Old 20-03-2014, 06:11   #22
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Re: Make a new rudder

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30" ???

I suggest that a composite shaft and associated framing is beyond the skill set of the average sailor... Just my opinion...
As to a carbon shaft- there's a discussion over here-

Carbon Fiber as a Replacement for Stainless Steel in Sailboat Rudders

Galvanic reaction will adversely effect carbon fiber, so one of the writers says.

We all want something to work and last a long time. Many ideas have been suggested here for material- carbon, stainless, fiberglass and Monel.

Carbon fiber like any new material has its appeal and is suitable for some situations. Thanks to carbon fiber The America's Cup brought the word "ugly" to competitive sailing in the appearance of the boats and the crew's outfits- black, a symbol of death- a hearse. Sort of like Ishmael's declaration of the Pequod in Moby Dick.

For my boat I suggest a Schedule 80 (thick wall) Stainless pipe of some sort would be more than sufficient for the stock/post. Removal of the rudder every year when the boat is on the hard would preserve the rudder even more.

Just for some humor consider this- make the stock from 2" PVC Schedule 40 pipe. Build the foil shape of the rudder from foam and then glass the foam over. Stick several lengths of 1/2" re-bar down the pipe and pour "water-plug" (or resin if you really want to be high-tech) down the pipe. Now, tell me- that's going to snap off? It will only after my transom has been ripped out.


If we ever buy another boat and it's a big blue water cruiser I'm certainly going to have the rudder and keel x-rayed.
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Old 20-03-2014, 06:39   #23
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Re: Make a new rudder

Here's a good link for getting an XLS spreadsheet for making an NACA foil shape.


Duckworks - Another Approach to Shaping Foils
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