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Old 15-01-2013, 18:06   #1
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Building Rudder - Carbon Fiber vs Fiberglass

I have build and shaped a new rudder for a 26' sailboat, and am trying to determine what would be best to cover it with. Carbon Fiber is obviously stronger, though more brittle. A friend said upon impact it could snap in half. The boat will have 40" of rudder in the water, is 16" wide and cord is 2".

Just want to use the best, as the prices are not all that far apart anymore. Also would like an opinion on the number of layers of CF or fiberglass.

I am also building a trim tab for the trailing edge, for self steering, and need to cover this as well. It will be thinner of course.

Thanks very much.
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Old 15-01-2013, 18:16   #2
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Re: Building Rudder - Carbon Fiber vs Fiberglass

I doubt that carbon fiber is necessary. I would recommend you use epoxy and glass. The West Systems web site has articles on rudder repair and you should be able to get a layup schedule from there.
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Old 16-01-2013, 09:13   #3
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Re: Building Rudder - Carbon Fiber vs Fiberglass

Thanks very much for the suggestion. I see you are in Winnepeg. I have thought about hauling my boat up there for some cruising. Have you cruised far up north?

Do you know what months would be best to cruise in your neck of the woods? Would hate to go when the bugs are in full swing.
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Old 16-01-2013, 17:28   #4
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Re: Building Rudder - Carbon Fiber vs Fiberglass

Quote:
I see you are in Winnepeg. I have thought about hauling my boat up there for some cruising. Have you cruised far up north?

Do you know what months would be best to cruise in your neck of the woods? Would hate to go when the bugs are in full swing.
Bugs? We ain't got no stinkin bugs! I was out all day and never saw one bug.

No, I have never sailed up north but have canoed a lot of north country. Best time to avoid the black flies is August, but it can get cool later in Aug. It can also be very hot.

I suppose you mean sailing in Lake Winnipeg? The south basin is very shallow and treacherous in a storm, which can happen quite quickly. I have never been in the north basin. They are linked by a narrows that has quite a current flowing through it. North of the Kasakeemeemisikak Islands there is a whole lot of wilderness with very few facilities.

Near the bottom of this page there is a link to download a cruising guide to Lake Winnipeg. It is in Word format.

Cruising Lake Winnipeg | Grindstone Park

I hope this helps
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Old 17-01-2013, 07:37   #5
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Re: Building Rudder - Carbon Fiber vs Fiberglass

Thanks very much. Any ideas on what weight/thickness fiberglass I should use on the rudder?
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Old 17-01-2013, 12:45   #6
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Re: Building Rudder - Carbon Fiber vs Fiberglass

Rdub,

The advantage of carbon over glass is that because it is stiffer you can retain the stiffness of the foil while making it thinner, longer, less chord, ect. Assuming you are working from an existing glass rudder, replicating it in CF won't provide much advantage other than a slight weight reduction. Where the weight reduction really gets going is when you can reduce the amount of material while at the same time make it thinner (less material again) all while increasing stiffness.

The reason stiffness is so important is that a stiffer rudder will flex back less, keeping a truer underwater shape, and minimizing the amount of foil deflected past the bearing. This helps reduce weather helm in the same way a balanced rudder can.

As for layup schedule. It really depends on the boat and the rudder design. Can you find the original rudder from the boat?
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Old 17-01-2013, 13:49   #7
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Re: Building Rudder - Carbon Fiber vs Fiberglass

I would use carbon only if:
- weight is an issue,
- stiffness is an issue,
- available equipment allows to build in carbon so that carbon prime properties are actually taken advantage of.

Otherwise go for well built glass.

BTW I found the hard way that, especially when building foils, it may be easier to use more layers of finer cloth.

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Old 17-01-2013, 16:37   #8
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Re: Building Rudder - Carbon Fiber vs Fiberglass

Weight is really not an issue, and I think it should be stiff enough. I am thinking that fiberglass will be easier and cheaper.

I was thinking of one layer of 4 or 6 oz glass. Are you thinking that 2 layers of something thinner would be better? If so what weight. Getting close to this step in the process after a bit more sanding.
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Old 17-01-2013, 16:47   #9
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Re: Building Rudder - Carbon Fiber vs Fiberglass

I think it would depend on how your rudder is built ?

Is it wood ? Perhaps a very light sheathing.

Is it foam ? Probably depends on the density.
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Old 17-01-2013, 16:48   #10
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Re: Building Rudder - Carbon Fiber vs Fiberglass

You don't say what the core material is, so I'm guessing wood

Either wood or especially foam, you don't want dings on the leading edge, especially near the bottom, to allow water ingress to the core.

I would trim off a strip (parallel looking from the side, flaring out at 45 degrees near the bottom) down the leading edge, and glass around the remainder of the core. (Having bevelled it away appropriately in preparation for the following step):

then: Stick the removed core back on, and glass it so it's structurally integral, but the leading-edge core is sealed off from the core of the main body of the rudder.

If it's too much to do this to the entire leading edge, at least consider a triangle at bottom.

ON EDIT: having personally had to go off the stern of a boat with a lightly sheaved wooden rudder to secure it after it broke in a broach, I am much happier that the owner/builder was persuaded to go for heavy sheathing on the replacement. (I tried to talk him into that when he built the first rudder, but uncharacteristically, he declined to rethink...)
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Old 17-01-2013, 18:07   #11
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Re: Building Rudder - Carbon Fiber vs Fiberglass

The rudder is transom hung, and has been constructed out of red cedar ripped from 2x6 & clamped and glued with Gougeon. Cord is 2".
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Old 17-01-2013, 18:27   #12
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Re: Building Rudder - Carbon Fiber vs Fiberglass

OK, We thought you were talking about a cored rudder with a metal rudder shaft.

But now, I think you are talking about a completely wooden rudder ?

In that case you probably don't need any strength from the skin, assuming that the wood is oriented properly and well glued.

The sheathing is only to keep the water out. A layer of epoxied fiberglass cloth would give you a very good abrasion resistant surface.

Post a picture of your work.
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Old 18-01-2013, 07:51   #13
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Re: Building Rudder - Carbon Fiber vs Fiberglass

I am a bit farther along than this. Hope the pics show up. Don't see a way to upload them. I can see they did not, will try again later.





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Old 18-01-2013, 08:15   #14
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Re: Building Rudder - Carbon Fiber vs Fiberglass

Here they are. Thanks
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