DIY CP23 Foil Rudder

[NateD]

After seeing everyone's homemade rudders I figured I would give it a shot. The process was fairly easy, although this was my first time laying fiberglass, and the inexperience shows. I think the total came out to about $100 in materials and probably about 10-15 hours.

I started by grinding off the bottom paint from the stock rudder.



I used a spreadsheet (http://www.duckworksmagazine.com/09/howto/foils/NACA0013-with-Jig.xls) I found on Duckworks (http://www.duckworksmagazine.com/09/howto/foils/index.htm) to generate a NACA 0014 template that was 14" long which would add 2" to the stock rudder. I printed the template out on 2 pieces of paper, taped them together, cut out the pattern, traced that onto some plywood, and cut out my wood template.



I cut 14"x31" pieces of 1" pink foam, along with a couple of thin strips to use as fillers, and epoxied it all together over the stock rudder. Because of the shape of the foil I modified my original plan and only had 1.5" of foam extend past the leading edge, and a 1/2" hang off the trailing edge of the rudder. Then I traced the foil shape onto the ends.





The actual shaping of the foam was easier than expected. For the life of me I can't remember what the tool is called, but it is a small hand tool with an abrasive screen. It did a good job of catching a lot of the foam dust. I think it took about 45 mins per side, maybe less. I was smoking a cigar, listening to the radio, and taking periodic breaks.



I ordered 12.5 ounce fiberglass mat from Defender, and had some West Systems epoxy on hand. I drilled a small hole in the bottom of the metal plate to stick a nail in to hold the rudder between my saw horses to do the fiberglassing. One of my last steps was to pull the nail out and fill the hole with epoxy just before painting it.



I thought I could get away with only one layer of fiberglass, but I ended up doing two. I applied my first piece as one large single sheet, which was very hard to work with. The picture below is with the first layer of fiberglass and a couple coats of epoxy. After putting 4 coats of epoxy over the glass, the rudder didn't seem firm enough, so I ended up adding another layer of 12.5 ounce mat over the first one. For the second layer I did it in 3 pieces, which were much easier to handle.



After attempting to fair the edges with thickened epoxy, I sanded the whole thing down with 60 grit to give the bottom paint something to bite. You can see some of my poor fiberglassing in this picture. Next time will be better....



Here it is on the boat with two coats of bottom paint. It will still be a few days before I get the boat back in the water, and I won't really have an opinion on it until we get some real windy days to see how much it reduces weather helm.

[JJ]

NateD

That foil looks great!  I just got done yesterday priming a NACA 0012 rudder for my CP 16.  I made a hot wire cutter and two foil templets like you did to cut the foam.  The foam came out smooth and didn't need any additional sanding.  I too put on two layers of fiberglass.   The fiberglassing and applying the epoxy were very time consuming and the hardest part of the project.  Over all it was a fun project and can't wait until the water temperature warms up to get my boat in the water and try the new rudder!

Happy Sailing!   JJ

[Greene]

Nice work.  I like the tip on putting a pivot pin on the bottom end.  It should make handling these much easier while they are under construction.  I've made one for my 16, 19 and now will need to do one for the 23.

Mike

[Bob23]

Nate: Very nice job. The tool is a Surform by Stanley and you are hereby a certified master Surform operator. Question: How wide is your rudder? I want to compare it to mine.
Thanks,
Bob23

[NateD]

Nate: Very nice job. The tool is a Surform by Stanley and you are hereby a certified master Surform operator. Question: How wide is your rudder? I want to compare it to mine.
Thanks,
Bob23

Bob, the stock rudder was 12", my foil is 14" wide by 31" tall with 1.5" of overhang on the leading edge.

[Bob23]

   That is about the same dimensions as mine although mine looks much thicker.

   Mine took forever to complete. I have an uncanny ability to over complicate my boat projects.
Essentially I did the same thing but I bolted foil shaped hardwood frames to the original blade, filled in with HD pink foam, sheathed it in 3mm Okoume plywood and glassed the entire blade.
   You'll love the increased performance!
Bob23

[NateD]

Well, I had a chance to try it in the water and I have to say I am unimpressed with my work. Winds were about 15-20 with occasional gusts to 30. This was the first sail of the season and I had 4 on board (including myself), 2 being non-sailors. I didn't want any excess drama and only put out about 3/4 of the jib, which had us moving nicely (and buried the rail in the gusts). Unfortunately there was still some excess weather helm despite not having the main up, but more annoying was a vibration that could be felt in the tiller (and sometimes in the boat) that varied with the speed of the boat and was obviously being generated by the rudder.

In my mind there are a couple of possibilities:
1. The rudder isn't fair enough. There were still some bumps and ridges which could be causing disturbances in the flow over the rudder.
2. The rudder bushings are worn and that could be contributing to the vibration. I will replace these, but I doubt they will completely fix the problem.
3. The foil ends a few inches below the water line and there could be an issue with water flowing over the foil and the few inches of stock plate at the same time, but looking at Bob's pictures, it looks like the foil ends below the water line, so I am thinking this isn't the cause of my vibration.
4. The foil may not be symmetrical. One of my crew brought up this suggestion, but I think if it wasn't symmetrical the water would flow faster over one side and it would create a "pull" to one side or the other (like a car out of alignment), which I didn't detect at all.

So I guess I will attempt to replace the bushings with the boat in the water and see if that improves things, then this fall I will sands off the bottom paint and try to fair the rudder better with thickened epoxy unless anyone has a better suggestion.

[cfelle2]

I have heard of beveling the trailing edge of a rudder to prevent vibration.  I know that Chuck Leinweber of Duckworks advocates this to resolve the issue.  Below is a link to a note sent by Tom Hamernik to Duckworks referring to it.  There is a chart which gives some trailing edge forms with there relative vibration amplitudes.  This would be easy to do and definitely worth a try.

http://www.duckworksmagazine.com/08/reports/feb-mar/index.htm

Chris

[fawsr]

Just an observation ...

I have a sunfish with with a wooden daggerboard. It had split and been repaired before I bought it from the PO. The wood daggerboard repairs are waterproof and fair, but not at all symetrical. One side has a longish raised vertical 'hump' at the repaired area. Sailing slowly, all is good, but when the boat begins to plane it REALLY begins to vibrate. Nothing more than annoying on that boat, but definately a strong vibration and at least in my mind, definately caused by the repair and resulting lack of symetry in the daggerboard.

[Salty19]

Nate- Bummer.   I bet it's not symetrical.    I doubt i's the length, mine hangs down several inches below the waterline on our 19.   Performance is exceptional, granted it's the IDA CNC machine cut version so it's perfectly shaped.

[NateD]

I have heard of beveling the trailing edge of a rudder to prevent vibration.  I know that Chuck Leinweber of Duckworks advocates this to resolve the issue.  Below is a link to a note sent by Tom Hamernik to Duckworks referring to it.  There is a chart which gives some trailing edge forms with there relative vibration amplitudes.  This would be easy to do and definitely worth a try.

http://www.duckworksmagazine.com/08/reports/feb-mar/index.htm

Chris

Chris, very interesting! In my earlier research I read something to the effect that the theoretical ideal trailing edge should taper to infinity, which isn't possible in reality and the point where you cut it off should be based on the strength of the material. I wasn't sure how strong the foam/fiberglass was going to be, so I have a very blunt trailing edge (about 3/8" wide).

fawsr, it's been a while but I can recall some vibration from the dagger boards on other dinghies too. I just did a little search and this site (http://www.glen-l.com/free-book/rigging-small-sailboats-10.html) says it is usually due to the shape (squared edges) or the fairing. I image symmetry plays into it too, maybe the vibration is partly due to water moving faster over one side creating a "pull" to that side, which stalls it slightly, and the tiller moves back the other direction with the pattern quickly repeating.

Either way it looks like I have to remove the paint, fair the rudder better, and bring the trailing edge to finer point.

[Bob23]

   Maybe theoretically the trailing edge should be sharp, but in practice, it should not. I tried to get a 1/8" flat edge but it ended up being about 1/4". I have no vibration and I know my rudder is symetrical.  It could be the bushings but I sailed mine with extremely sloppy bushings due to a corroded gudgeon and experienced no vibration.
   Is there any play between the rudder blade and the rudder housing? Before I added zincs, the hole wore and there was play at that location. I since have overdrilled to 3/4", added nylon bushings and a new 1/2" stainless steel bolt. Voila! no play!.
    Maybe you could cut a plywood template with a true symetrical foil and use it for a guide. Keep us posted...sorry to hear your first attempt didn't quite work.
   Remember that the 23's are known for thier inherent weather helm. I eased mine a bit by raking the mast forward about 2 degrees. Looks wierd but it works.
bob23

[hockeyfool]

I also want to have one of those - but dont have the shop to do it: If someone can do a retro foil for over my blade I will
be able to pay a fair price for it !

[cfelle2]

IdaSailor makes a replacement rudder for the compac 23.  See link below.

http://www.idasailor.com/catalog/product_info.php?cPath=24&products_id=36&osCsid=7064f45435b470ad2803efd0aa6df94b

Chris

[NateD]

*UPDATE*

So I was irritated by the vibration from the rudder, so I brought it back home and ground all the bottom paint off to fair the foil and extend the trailing edge to bring it to a finer point. After grinding the paint off I put a tape measure up to the trailing edge to see how thick it actually was and I was surprised to find it was about 3/4"! The stock metal rudder was 3/8" of an inch thick, so my goal was to bring it down to about 3/8".



First I took it down to 1/2" with thickened epoxy, which I was then able to cut a clean trailing edge with a jig saw. I took it down to the boat and tested it out and the vibration was much better, but still there. I added more epoxy and get it down to 3/8" of an inch, painted it again, and tried this weekend. Success!



From what I read trying to figure this thing out, as the water comes off the trailing edge it creates little vortices. My guess is the 3/4" trailing edge throws relatively larger vortices than a 3/8" trailing edge, which is what was causing the vibration. Or it could be that I was able to achieve a much "cleaner" edge cutting the trailing edge with the jig saw compared to the fiberglass wrapped around the foam (creating more of a rounded edge).

As my rudder stands now I only have about 1.5" of overhang on the leading edge, and with all the epoxy buildup to get the trailing edge thinner, the trailing edge is now about 1.75" past the metal plate. The rudder handles better than the flat metal plate, but it doesn't have that "power steering" feel that some talk about. I think if more of the surface area was moved forward the balance would be better.

If I did it again I would still make a 14" foil with 2.25" of overhang on the leading edge and the trailing edge tapering down to the metal plate so that the trailing edge of the rudder would essentially be the metal stock with a layer of fiberglass (or just thickened epoxy) over it.

You live, you learn, and my next one will be better.