Building a Rudder for 23' boat - SailNet Community
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post #1 of 15 Old 09-11-2008 Thread Starter
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Building a Rudder for 23' boat

I am building a replacement rudder for my Coronado 23. I have the blueprints for the dimensions. I have read on another forum about someone who built one for the same boat using two pieces of 5/8" marine grade plywood (held together with bolts and epoxy) and glassing it to achieve a thickness of 1 1/2", in which the builder noted success and long term use of said rudder. I am just looking for any thoughts, advice, or comments from anyone who has done this type of thing before. Thanks in advance.
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post #2 of 15 Old 09-11-2008
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A few years ago I built a rudder for My Catalina 22 MKll fin keel. I did alot of offshore racing with the boat and the rudder would come out of the water when cresting a wave.
Because the keel was apx. 5 feet down, I had plenty of room to go down with the rudder.. Design was the next concern.. I made a templet of the fin of a blue whale about 5 feet tall.. built a box of 2x4s and poured 2-part foam into the box.. when it cured, I started grinding the foam to copy the shape of the whales fin..
once the shape was finished, I covered the foam with 3 layers of carbon fiber and finished with epoxy paint...
The fin was about 5 feet tall but only about 8 inches for-to-aft..
Took alot of 1st places with that design....
The foam (2-part) becomes very hard after curing and workable with a grinder to get the right shape.. and the glass work was really easy....
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post #3 of 15 Old 09-11-2008
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How is the rudder blade going to be attached to the rudder stock?? is it a transom hung rudder using pintles and gudgeons??? If so, that should work fairly well.

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It did hang off the rear of the boat and the tiller was set to rest in a notch in the forward part of the rudder.. The hinge point was two pieces of aluminum strap, bolted solid to the tiller and a thru bolt on the tiller.
Wher the thru bolt went thru the rudder, I epoxyed a dowel of teak and drilled out the center for the bolt.. the dowell was aroung 1 1/2 inch and the bolt was a 1/2 inch.. when the tiller (hinged) was pulled down over the rudder, it fit the notch and thus held solid and had NO slop to it.
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post #5 of 15 Old 09-12-2008 Thread Starter
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sailing dog, the rudder I am planning on building for my C23 is mounted on the transom with pintles and gudgeons. I wasn't sure if you were asking about my original question or the post about the foam rudder in the first reply. As I am quite new to this type of project, as well as the main use of my boat being daysails and little cruises and not racing, I hope to keep it as simple as possible. Thanks.
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post #6 of 15 Old 09-12-2008
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The question was directed at you. Given that the rudder is a stockless design, being held on by pintles and gudgeons, I think you'll be fine with making a rudder up that way. I would use two 3/4" pieces of ply though, not 5/8" if your goal is a rudder 1.5" thick. You'll want to shape the rudder to a NACA profile, and then glass over the wood and fair it with thickened epoxy. If you use microballoons for the epoxy thickening agent, don't forget to skim coat it with epoxy after sanding it to seal the microballons and prevent them from absorbing water.

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her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Last edited by sailingdog; 09-12-2008 at 08:10 AM.
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post #7 of 15 Old 09-12-2008 Thread Starter
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thanks sailing dog. i guess my thought on the thickness of plywood was that the glassing would add the additional 1/4" total on the thickness of the rudder (1/8" per side) if I used two 5/8" pieces together, but it sounds like I may have overestimated how much thickness the glassing process would add to the rudder. I am shooting for 1 1/2" based on my old rudder and the width of the band that bolts on the pintles. Will the glassing add any noticable width to the finished rudder? thanks for your help and advice.
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post #8 of 15 Old 09-12-2008
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Yes, fiberglassing the rudder will add some thickness..but you will be shaping the plywood to an airfoil shape (in an ideal case), and that will remove some of the thickness of the plywood... so starting at 1.5" thick would probably be better than starting off 1/4" shy of it.

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thanks sailing dog. i guess my thought on the thickness of plywood was that the glassing would add the additional 1/4" total on the thickness of the rudder (1/8" per side) if I used two 5/8" pieces together, but it sounds like I may have overestimated how much thickness the glassing process would add to the rudder. I am shooting for 1 1/2" based on my old rudder and the width of the band that bolts on the pintles. Will the glassing add any noticable width to the finished rudder? thanks for your help and advice.

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her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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post #9 of 15 Old 09-12-2008 Thread Starter
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Right on, Sailing dog. That makes good sense, I will definitely be shaping the rudder for good flow. I read a good thread on rudder shape on this forum and feel like I have decent idea of general shape guidelines. Thanks for helping me think this through. It will be a good learning experience for me I am sure. As you can probably tell, this is my first boat and certainly a bit of a project. (Mostly interior rebuild, with the exception of the rudder) After I learn to fix my boat, i will actually be able to work on my actual sailing skills.
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post #10 of 15 Old 09-13-2008
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It's really helpful (and easy) to loft your NACA profile onto fine graph paper and glue that to some Masonite. Carefully shaped to your line, it provides a half-profile template for checking your work. You'll need accurate centerlines down the the leading and trailing edge to index your template off of.

Have a go -- by the end, you'll know how to build a rudder.

Buccaneer18, Grainnia
SJ21, Diarmuid
Albin Ballad 30, Fionn
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