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Old 22-08-2008, 04:37   #16
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Quote:
Originally Posted by koreasailing View Post
Every site I've checked has said to use hard wood. And as far as I know, fiberglass doesn't flex that well. Is it possible to have the wood be more flexible than the glass and have the skin rupture because of too much flex?

I'm looking into the wood rot thing now. If cedar is okay, I may use that. The place I checked yesterday didn't have African Mohogany or Oak but they did have red cedar.
Make sure you stipulate clear grain, NO knots. I would put a few layers of uni directional cloth then a biaxial, all 450 gram per square meter. Or better yet one full layer of uni then 4 or five layers down the thickest part about the same width as the flat area, slightly widest for the first then each one slightly narrower. Then cover the lot with a layer of biax. This gives a stiff stem up the middle which takes the bending loads and the cedar is just a core.
As said before don't try and wrap the glass around the trailing edge, just lay it past then grind it back later to square and straight. Don't grind it back so far as to expose the cedar.

This is basically how my daggers are made. They are 3 meters by 600mm but have 10 layers of uni 150mm wide,each side, forming the stem up the middle.

Mike
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Old 22-08-2008, 09:00   #17
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Koreasailing, You are talking about a rudder for a 22' Catalina, not a Maxi racer. The loads are simply not that great. Since this is your first (I assume) building project, JUST DO IT. Make it out of plywood, for starters. It's cheap, it's easier to fabricate, and if you epoxy and glass it, perfectly strong and functional for your application. Hard wood, soft wood, foam, etc. are options, but they are more complicated from a building standpoint, require possibly more skills than you have acquired, yet, and keep you from going sailing, which was your original objection for ordering a new, replacement rudder from Catalina.

This is the most common problem builders have: the inability to choose a course and carry it out. Instead, we debate with ourselves and others, forever, and somehow the original project falls by the wayside while we get jazzed by the discussion. It's one of the reasons why two out of three boats never get finished. Ask any of the real builders on this forum. I'll bet they will concur.
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Old 22-08-2008, 09:58   #18
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.
This is the most common problem builders have: the inability to choose a course and carry it out. Instead, we debate with ourselves and others, forever, and somehow the original project falls by the wayside while we get jazzed by the discussion. It's one of the reasons why two out of three boats never get finished. Ask any of the real builders on this forum. I'll bet they will concur.

Paralysis by analysis.
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Old 22-08-2008, 10:57   #19
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Roy and Charlie are absolutly right. This ain't rocket science! Plywood will work just fine. Marine if you can get it, ACX if you can't. Laminated cedar would be better but more work. A compromise would be to use a central core of say 1/2" ply and glue cedar to the sides and shape it down then glass it. This keeps things flat and gives you reference lines while shaping. But like Roy says, just pick a method, "git 'er done" and have some fun in the process.

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Old 22-08-2008, 20:54   #20
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Agree but...

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Koreasailing, You are talking about a rudder for a 22' Catalina, not a Maxi racer. The loads are simply not that great.
I agree but the rudder failed on a short ocean passage and I understand koreasailing's concern to make it "stronger than new." Which brings up the next issue.

If the rudder is built wo withstand whatever force broke it, how about the pivot points? And if you beef up the pivot points points how about the transom strength.

Analysis paralysis. I like it.
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Old 24-08-2008, 00:46   #21
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Of course ply will work just fine. But it will break again. As I said earlier, ply does not like cyclic stress. It eventually fails. A new ply rudder will work just fine until it has done ruffly the same number of seas miles, then it will fail. Hence why the use of solid timber is used more now. It takes no more work, but certainly a different approach. There is more work up front in the preparing and laminating the pieces of timber, but the shaping is much easier than trying to shape ply. Provided you want shape of course. If you want a plain straight piece for a rudder, then the easiest would indeed be ply. If it is a quick emergency rudder, then once again and plain ole piece of ply would be easiest. But if you want to go to a proper hydrodynamic shape and strong long lasting piece of rudder, then laminated pieces of timber is the best way to go.
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Old 24-08-2008, 09:05   #22
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Why not build the plywoood rudder first, since it is Koreasailing's first (it sounds like) boatbuilding project. As we all have learned, the first projects teach us a lot about using the tools and adhesives and techniques. Then, when he gets bored with sailing his low tech rudder, he can learn, experiment and perfect his technique on a more sophisticated rudder. But, in the meantime, he is actually doing what he originally intended - sailing.
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Old 24-08-2008, 21:49   #23
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Hi guys,


Well... the rudder is still in the planning stages. After going to 2 large timber yards and calling 3 more, all I ended getting was a bad case of frustration. Plenty of non-marine grade plywood and stacks of pine, but no cedar or spruce.

Luckily I think I do have a good lead on some wood throught the Busan Yachting Assoc. I'm hoping to score some kind of wood this week. If not, I'm seriously considering using normal ply or pine and just epoxying the hell out of it.

As some of the posters said, Just do it. Come hell or high water, a rudder will be made this weekend, if even a temporary one. So here is the next question. Regular ply or pine?
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Old 24-08-2008, 22:31   #24
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I wonder about a rudder of solid fiberglass glass if you can find no suitable core in your neck of the woods.

Heavy as heck...

Zach
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