Building a new rudder

[LeighWebber]

I'm building a new rudder for my Columbia 43 Mk III (https://sailboatdata.com/sailboat/columbia-43-miii). The old one was built with an internal steel panel plus horizontal steel ribs, filled with foam and covered in fg. Like so many of this design, the thing had been leaking for years. Upon inspection, the steel was badly rusted (mild steel, not SS). Although I could have cleaned it all out, welded in some repairs, then recovered the entire thing, I decided to build a new rudder from scratch.

I started with a SS rudder post the exact size of the old one (see attached PDF drawings). I had a local machine shop weld four 3/4" SS rods to the post. Each rod passes through a hole in the post and is welded on each side, producing an immensely strong "web". I'm now building the rudder body, which is composed of 15 red cedar boards laminated with formaldehyde glue. The boards are all 2 x 6 (i.e. 1.5 x 5.5) and each is drilled to fit over the rods. At the end of each rod is a SS washer and nut which will hold the rudder body snug into the post. The rods themselves do not extend all the way to the aft edge of the rudder: the final couple of laminate layers are held simply by the glue. This allows me to (1) completely enclose the rods and nuts, and (2) shape the trailing edge of the rudder to a narrow final taper. I will cut and sand the entire rudder body to an airfoil shape. The resulting rudder actually weighs less than the original -- and will also have some buoyancy to offset some of the weight.

The leading edge of the rudder snugs into the post, and I will shape the wood so that it wraps tightly around the aft surface of the post. I'll glue the leading edge of the rudder to the post with 5200. This is not for attachment strength (the 4 rods + nuts do that), but is instead to provide a seal to minimize water incursion into the rudder. I'll make sure the 5200 fills the (small) space between the outer rod surface and the interior of the holes the rods pass through.

The lamination procedure will go like this:

1. Pre-cut each board to its approximate airfoil shape.
2. Attach the inner (leading edge) boards to the post, using 5200. Clamp and allow to cure.
3. Laminate additional boards in groups of 3 or 4, using formaldehyde glue and lots of pipe clamps. Allow the glue to completely set before adding the next set of boards.
4. Add the nuts and washers as the relevant boards get added. Tighten them, but add no sealant or caulk (they will be completely encased in the wood rudder body)
5. When the entire rudder is laminated, do a final shaping, smoothing, etc.

So here are my questions for the group:

(1) Am I nuts to be building a wooden rudder to begin with?

(2) If you were doing it, would you use another species of wood? I chose red cedar mostly for its light weight.

(3) Should I use something like LifeCaulk to seal the leading edge of the rudder to the post? I'm not concerned with future removal, because if this thing has to be rebuilt, the entire wood body would have to be cut away. My main concern is to minimize water incursion between the SS post and the rudder body, to avoid crevice corrosion.

(4) What kind of paint(s) should I use for the rudder body? The SS post will remain bare.

[dannc]

There is a multipart article on the Morgan's Cloud website about old rudders and rebuilds. One has to pay for the site but it is worth the money.

https://www.morganscloud.com/2020/03...oblem-defined/

Part 2 talks about costs to repair and such.

Later,
Dan

[Cheechako]

The easy method would be to use your old fiberglass rudder shell, cut it longitudinal along the post and peel it off. put it on your new SS structure using it as the shape. Then laminate the entire new surface around it. Fill it with Epoxy or other casting resin etc.

Your wood method will work, and cedar is great. I guess I would use 5200 around the post and saturate all the wood with epoxy. I would think of the wood as just shape really. Cedar is fairly soft so I hope the metal doesn't slowly rub it until the rudder is loose on the post.

[ilCigno]

It’s perfectly possible to build a new diy rudder, with equal or better performance than anything on the market. I have replaced my rudderblade myself some four years ago and the effect of the new rudder was dramatic, as if I had a whole new boat. The reason was that I studied the shape and properties a well designed rudder should have. A mere copy of the old blade is in most cases not such a good approach. I have gathered the calculations needed for the design in an easy to use spreadsheet, along with a short manual. As it is in Dutch now I’ll translate it and post it on this forum shortly. It will be unprotected and free for anyone to use, or even to modify if needed so.

[LeighWebber]

Originally Posted by Cheechako

The easy method would be to use your old fiberglass rudder shell, cut it longitudinal along the post and peel it off. put it on your new SS structure using it as the shape. Then laminate the entire new surface around it. Fill it with Epoxy or other casting resin etc.

Your wood method will work, and cedar is great. I guess I would use 5200 around the post and saturate all the wood with epoxy. I would think of the wood as just shape really. Cedar is fairly soft so I hope the metal doesn't slowly rub it until the rudder is loose on the post.

The old one was in such bad shape internally, there was no way to peel off the old shell.

I was thinking of pouring thinned epoxy down each hole just before securing the nuts. This would pretty much eliminate any movement. There isn't much movement possible anyway, because the holes are 7/8 and the rods are 3/4, leaving at most a 1/16 gap. But you just can't drill 4,000 holes (felt like) and have them all EXACTLY in the right spots. All the boards fit on the rods, but they don't wiggle, because of the various teenie position errors in the holes. But thinned epoxy should take care of that anyway.

I think I will paint the outside of every board with thinned epoxy just to ensure that water can't easily get to the wood. Then maybe some fairing epoxy I can sand super smooth before painting with anti-fouling. Plus this boat is in Lake Superior, so I think the rudder will last a looooong time.

[LeighWebber]

Originally Posted by ilCigno

It’s perfectly possible to build a new diy rudder, with equal or better performance than anything on the market. I have replaced my rudderblade myself some four years ago and the effect of the new rudder was dramatic, as if I had a whole new boat. The reason was that I studied the shape and properties a well designed rudder should have. A mere copy of the old blade is in most cases not such a good approach. I have gathered the calculations needed for the design in an easy to use spreadsheet, along with a short manual. As it is in Dutch now I’ll translate it and post it on this forum shortly. It will be unprotected and free for anyone to use, or even to modify if needed so.

Dank je!

[ilCigno]

I have the translated files ready, but it seems to be impossible to upload anything but a .doc or a .pdf file to the library. I've asked the mods for assistance.

[Searles]

Don’t know the model of the project boat ,l have been in the boatbuilding and design foR nearly sixty years ,to me the o,d of the stock is ok but the wall thickness at .2 seams a little on the skimpy side would be happier with .375 in centre less ground 316L, the design would be better upgraded to a more efficient shape I e more area at the top where the water is disturbed and thinner ,and a lower area at the bottom where the water is more stable,plus have about 10 percent of the area fwd of the centre of the stock, at least 3 layers of ten oz cloth glass in epoxy oll over then fair . Having built and rebuilt many production boat rudders I know wot works . Hope this helps ⛵️⚓️��

[LeighWebber]

Originally Posted by Searles

Don’t know the model of the project boat ,l have been in the boatbuilding and design foR nearly sixty years ,to me the o,d of the stock is ok but the wall thickness at .2 seams a little on the skimpy side would be happier with .375 in centre less ground 316L, the design would be better upgraded to a more efficient shape I e more area at the top where the water is disturbed and thinner ,and a lower area at the bottom where the water is more stable,plus have about 10 percent of the area fwd of the centre of the stock, at least 3 layers of ten oz cloth glass in epoxy oll over then fair . Having built and rebuilt many production boat rudders I know wot works . Hope this helps ⛵️⚓️��

See my initial post re the model, with a link to sailboatdata that shows the shape of the original rudder. With full skeg, the post thickness should be ok, as it is supported top and bottom. I like your idea regarding having a portion of the rudder extend forward of the post, which would have to happen below the skeg, of course. It would produce a sort if J shape. Increasing the size near the top and reducing it at the bottom (plus the elongation to produce the forward-of-the-post portion is an intriguing idea. I'm going to sketch it out and think about it. I haven't started glue-up yet, so I can change things fairly easily.

[LeighWebber]

Originally Posted by ilCigno

I have the translated files ready, but it seems to be impossible to upload anything but a .doc or a .pdf file to the library. I've asked the mods for assistance.

Can you save the files in PDF format? Easy to do if you have a "print to pdf" printer driver installed (plenty available for free online). Or email the files to me and I'll convert them for you. My email is my name like it shows on the left at live dot com.

[ilCigno]

@Leigh, I've send you a mail which explains why just a pdf doesn't work in this case.

[Time2Go]

Check out “Sail life”
on Youtube. Mads goes into some
detail about his rudder rebuild
Cheers
Neil

[LeighWebber]

Originally Posted by Time2Go

Check out “Sail life”
on Youtube. Mads goes into some
detail about his rudder rebuild
Cheers
Neil

Yes, I saw that. Many differences between our boats and rudders, though.

[Spot]

Looks like a fun project Leigh.
What foil are you thinking? 12 to 14%?
Image was made with the desktop version of finFoil.io (also available online)

I would recommend glassing along with resin. The wood alone will expand and contract, cracking the epoxy and allowing water intrusion, which promotes even more cracking. Three Minnesota winters and I have lost much of the epoxy (used as a finish) that wasn't glassed on my small plywood boat. The glassed areas look almost new.

[Nicholson58]

Wood filler - ugh!

I rebuilt our monster rudder. It was SS skeleton with foam and fiberglass, all turned to mush

I would never permanently immerse anything in water that I didn’t want saturated eventually. The first law of fluids is water leaks.

I used exclusively all materials from Fiberglass , Epoxy , Composites, Carbon Fiber - U.S. Composites, Inc.

Use 635 THIN epoxy for all layup. I built and shaped the core of 635 THIN and 3M micro balloons. 3 total gallons resin and two 4 gallon balloons Fillers

Use five gallon buckets and a drywall mixer with a heavy duty 1/2” drill. GO SLOW!

Kick time in a cool basement is hours and the cure speed lets you pour five inch thick sections. 3 days before it’s hard enough to sand.

This core is 100% waterproof forever.

After shaping, I had it vacuum bagged with carbon fiber.

See my photos
https://www.cruisersforum.com/galler...d=49581&page=3