Foiling the 23's rudder

[Greene]

Before I start on this foiling project on the 23, I was wondering what dimensions others ended up with.  On our 16 and 19 rudders I added about 1" on the leading edge and kept the trailing edge and length original.  I believe others added as much as 2" to the leading edge and I was reading on another forum that a guy had added 12" to the depth or length of the original rudder. 

So, what did you do with yours and what were the results?

Mike

[Bob23]

Mike:
  My original blade, when fully down, is past the keel (in depth) by about 10 inches. If I were to do this again, I'd shorten the blade before the forming of the new foiled blade. I'd also re cut the front edge of the blade to make it sit plumber when fully down.
  I don't have my rudder here but I'll stop over and get some measurments for you tomorrow. I think I added about 2 inches to the leading edge but I'll check it.  Here are a couple of shots, you may have seen these in International Rudder Magazine:


Bob23

[Greene]

Mike:  Here are a couple of shots, you may have seen these in International Rudder Magazine:
Bob23

Brenda doesn't let me subscribe to magazines like that.  I spend too much time looking at the centerfold pictures instead of reading the articles.

Mike

[NateD]

I would really appreciate the measurements as well. I went down to the boat this weekend to remove the stock flat rudder to bring home and add a foil before spring. The boat was under a tarp and I removed the rudder before measuring (doh!), but it looked like a max clearance between the rudder and the transom was only about 2.25" tops, so I was planning on only adding 1.5" to the leading edge. My understanding of fluid mechanics and sailboat design is pretty minimal, but my understanding is that adding surface area forward of the rudder stock will "balance" the rudder and help to reduce weather helm, so I would like to move the leading edge forward a bit. I've also read that creating any kind of disturbance in water flow slows the boat, so I was planning on the foil coming up and out of the water (so the flow is uninterrupted by going from foil to flat stock underwater). On Bob23's beautiful rudder it looks like the foil remains fully submerged, so there is no physical restriction to the amount of leading area that can be added.

I wasn't planning on adding any depth, but I haven't fully thought that out yet. I was planning on using just foam and fiberglass without a harder leading edge material, so I don't want to make it any more vulnerable to grounding than it already is.

Anyone have any insight into what weight fiberglass to use?

[Bob23]

Mike:
   I understand. Linda (my admiral) caught me with IRM and it was embarrasing, to say the least. "Sure, I don't look like those new rudders in the centerfold, but who else would put up with steering you for the last 32 years?" She had a good point. I threw out all my old issues, but kept a few beauties for, let's say, future research!
   See what I mean in the photos about the rudder not sitting plumb? If the wood blade itself would sit plumb, that would mean more of the blade being forward resulting in less weather helm. Maybe I'll try to recut the top of the blade to achieve this.
Nate:
   You are correct in your assumptions about how the rudder behaves in water, at least as far as I'm concerned, your'e correct. I would put some kind of hard leading edge on the blade but it could be done in foam and glass, especially if it's a prototype. I'm just an incurrable wood nut so that's why my is done in wood. It has a foam core. And a mahogany leading edge with white oak top and bottom. All stuff I had lying arround except for the 3mm okoume plywood which I will not repeat what it costs me. I still have 2/3 of a sheet left over for the next project.
   Here are a few construction photos:



Bob23

[Greene]

Is that backward rake typical?  Neither my 16 or 19 had that rake.  I didn't notice it on the 23 when I picked it up, but my friend is the one who removed the rudder for the long trailer home.  That looks like it would really add to the weather helm.  I'd be tempted to cut a bit off the top shoulder of the aluminum to allow it to pivot closer to vertical.

Mike

[Shawn]

Bob,

For 'next time' shaping the foam looks like it could be a bit easier/quicker/cleaner if you try the hot wire trick to cut it. You could likely do the entire blade in a single pass if you made an inverse form and used a bow to hold the wire.

Sort of like in this video...

http://www.youtube.com/watch?v=R0ZCnR_g6ZU&feature=related

Except using a bow for the wire with forms on both ends. I think most use a guitar string for the wire and things as simple as a small battery charger for the power supply.

Shawn

[brackish]

Is that backward rake typical?  Neither my 16 or 19 had that rake.  I didn't notice it on the 23 when I picked it up, but my friend is the one who removed the rudder for the long trailer home.  That looks like it would really add to the weather helm.  I'd be tempted to cut a bit off the top shoulder of the aluminum to allow it to pivot closer to vertical.

Mike

Don't think it is typical.  I have the Com Pac version of the foiled rudder, the one that is stock on the 23's these days.  Every once and a while the tang that holds the rudder down will slide out to the side allowing the rudder kick up very slightly and  form that angle.  I don't have to look back to see that it has happend, weather helm increases dramatically.

[NateD]

Is that backward rake typical?  Neither my 16 or 19 had that rake.  I didn't notice it on the 23 when I picked it up, but my friend is the one who removed the rudder for the long trailer home.  That looks like it would really add to the weather helm.  I'd be tempted to cut a bit off the top shoulder of the aluminum to allow it to pivot closer to vertical.

Mike

The rake isn't typical. You can see in Bob's construction pictures that his wood foil guides stick out a little bit more at the top of the rudder than they do at the bottom. The only picture I have of the stock rudder from the side is a little obscured, but it looks like the stock blade is straight down.

[Greene]

I should have known Bob would be half a bubble off center.

Mike

[Bob23]

Actually, Nate:
  What you are looking at is the top frame sticks out a bit because it is on the angled part of the original blade. The overall shape of the rudder follows the line of the original aluminum blade.
When I first bought the boat, I suspected that the rudder was not original and emailed Gerry a photo of it. He confirmed it was the stock rudder. I plan to recut the leading edge of the aluminum blade where it sits inside the rudder head to achieve a more plumb rudder.
  The only thing I can account for the un-plumbness of my rudder is that I did redrill the hole in the rudder head. It was quite corroded. If I mis-drilled it, that would make it sit as shown in the photo. Here is a shot of the original blade taken not too long after I purchased this fine craft:

bob23
Half a bubble off center on a good day!

[Bob23]

   This is the first time I've looked at before and after pictures of my rudder hanging off the boat. Indeed, as pointed out, she sits a bit raked back- a bad thing indeed. I must have been careless in drilling the new hole for the pivot bolt, which is now 1/2" ss sitting in nylon bushings. The main body of my wood blade is parallel to the original leading edge of the aluminum.
   I'm hoping that when this is corrected, I'll continue in my quest to banish weather helm from my boat forever. Or just lessen it a bit.
   Thanks, gents, for pointing this out. It may this weekends project! I'll take a few photos and look at them side by side.
Bob23

[Bob23]

Well, the mystery is solved! It gnawed at me that I could have created a rudder with aft rake until it dawned on me: In the photo, the rudder was pulled back a bit and the bolt tightened, all for no apparent reason. I knew it was plumb so I installed it today and took these shots:

Here is the 1/2" ss bolt with some ss and nylon washers:

And, last but not least, a shot of the nylon bushing I use to try to isolate the aluminum rudder  from the ss bolt and also reduce wear:

Cool, huh. Measurements to follow.
bob23

[newt]

Bob,
As you know, I am welding part time in a class. Have progressed past acetylene torch, and now in the middle of MIG. (anyone want any jackstands or  painting platforms out of cold steel??) Will start TIG soon, and plan on welding a rudder with Al stock. Have already cut the rudder 6 inches shorter, but plan to make it longer and of course foiled. Sorry I am taking so long to get these projects done, but I just insist on doing em the way that will last.
Over the next year, when I get good at TIG-
All metal Bobstay/bowsprit with two anchor holders and perhaps twin forstays.
Metal doger with boomkin and perm. solar panel.
improved boarding latter (bigger steps)
Cutter configuration
Oar aux instead of motor
watertight
improved cleat design

[Greene]

You are an ambitious man.  That is quite a list of improvements.  You will love TIG welding.  I did a lot of stainless welding back when I was doing industrial maintenance and always enjoyed TIG the most. 

Mike