Stock Rudder Blade Needed for Shade Tree Engineering Experiment

[Pacman]

I have an idea for a new way to make a balanced NACA foil rudder that I would like to try as an experiment.

If you have installed an aftermarket foiled rudder and have a stock one laying around that you would be willing to donate for experimental purposes, I can pay shipping costs.

I would keep everyone informed of the success or failure of the experiment.

If it works, everyone will benefit.  If it is a failure, I'll keep trying.

Thanks,

Dave

[capt_nemo]

Since you only need the bottom plate portion you might be able to get one cut out of a piece of scrap aluminum plate from a sheet metal shop at reasonable cost. Or, for early experimental purposes, use an epoxy coated 3/8" piece of harwood or plywood as a base from which to start.

By the way, I've been thinking about a foiled rudder for my Sun Cat and am considering making one since they are so expensive. I'd be very interested in any experimental efforts to fabricate one at home. I think the CP-16 and Sun Cat call for the same rudder, a NACA 0012 foil with 12" chord and about 37" overall length (bottom rotating piece only).

capt_nemo

[Greene]

Just search the forum for Foiled Rudders and you'll find a lot of good info.  This is one that I started that has ten pages of info and a bit of foolishness to boot.  If I remember correctly there is even a bootleg photo of Bob's original effort. 

http://cpyoa.geekworkshosting.com/forum/index.php?topic=3106.0

Mike

[Pacman]

More detail on the project:

The reason I want another rudder blade is that I plan to add 2" to the leading edge to create a "balanced" rudder.

Then I will make a foiled rudder (NACA 12) as per the link above - but using a 14" chord instead of the stock 12" chord.

This might work very well if it simply lightens the tiller.  However, it could be too much of a good thing if it eliminated weather helm altogether. 

I want to retain a small amount of weather helm but with a light feel on the tiller.

Although I am confident that a stock 12" chord faired to NACA 12 alone would give excellent results, this experiment is to see what happens with a rudder that is both balanced and faired to the NACA shape.

[Bob23]

Pac:
   I don't know on the 16's but on my 23, adding 2 inches to the leading edge didn't eliminate the weather helm. I built my stock aluminum blade into a wood foiled blade (NACA 0014) and it has vastly improved my 23's performance. It also vastly helped to deplete my $ but that's only because I have a tendency to over complicate things a bit. I think there is a thread on the 23 section about my wood foiled rudder blade.
   The reality is this: The foil shape in conjunction with the longer leading edge greatly lessened the weather helm but the body of my blade is addmittedly too big so that I feel contributes to the still ever-present weather helm, albeit, much less than before.
   Hey, it was the first rudder I ever made-what did I know?
Here's a secret photo:

And another:

Bob23

[Pacman]

Bob23,

That is really great!

You are a kindred spirit indeed.

I notice that your rudder appears to extent past the trailing edge of the aluminun stock rudder.  If that is the case, it might mitigate the effect of extending the leading edge to some extent.

All that aside, it is beautiful.

Thanks.

[Bob23]

Thank you, Pac:
   Yes, I think you are right. It wasn't supposed to get quite that big but you know how things go sometimes...not the way you planned. I think the sheer largeness of the blade detracts from it's perfomance but, all in all, it came out pretty good. Cost was about equal to the space shuttle and in terms of time spent: Well, glaciars moved faster than the progress on my rudder. But I've used it for 2 summers now and it's a keeper. The next one, if there is to be one, will be a lot shorter and not made of wood. Although I still have 2/3 of a sheet of 3mm okoume plywood left!
   I have construction pictures if your'e interested.
bob23

[Mark F.]

Dave:

I've got an original rudder from my 1990 Com-Pac 16 you can have for the cost of shipping.  I live in Jacksonville, FL.  Let me know if you're still interested in doing this.

Mark

[Pacman]

Mark,

PM sent.

Dave

[Pacman]

Mark,

Thank you very much.

Having a second rudder to work with will allow me to test the results of my experiments against a stock rudder that will be used as a standard.

My first step will be to simply add 2" to the leading edge to create a "balanced" rudder.  This will be done by adding aluminum plate to the leading edge but without fairing of any kind.

The "balanced" rudder will be compared to the stock rudder blade.

The second step will be to fair the "balanced" rudder to a NACA foil shape with a 14" chord.

The "fair and balanced" (I just couldn't resist) rudder will be tested against the stock rudder blade.

Then, I may fair the stock rudder blade to the same NACA foil shape with the stock 12" chord.

If I do that last step, I will be able to compare faired rudder blades of 12" vs 14" chords.

Right now, I expect that the 14" chord NACA rudder blade will perform best.

Thanks again Mark.

[Bob23]

Mark:
  I'll be interested to hear of your findings, although if it were me, I'd not waste my time just adding the 2" to the flat plate blade. But wait, I take that back- anything in the quest for knowledge! I don't expect that you'd notice much difference between the 0012 and the 0014 although, again, I for one will follow this thread with interest.
  I've toyed with the idea of converting my CP23's rudder system to and inboard rudder ie, rudder shaft installed running through just forward of the transom and a fixed, nonkick-up foiled blade. I wouldn't make such a drastic alteration without consulting with a designer who is familiar with the 23. However, I feel this change would have the possiblity of removing all weather helm, although I do admit to knowing that weather helm is the result of much more than just  rudder placement.
   If I remember correctly, there was a recent article in Good Old Boat by designer Robert Perry about weather helm. He noted that some boats just have it. That article may aid you in your investigations into the world of rudder design.
Bob23

[Pacman]

Bob,

I did not explain my project well so I'll try again:

First I want to compare flat blades with chords of 12" (stock) and 14" (with 2" added to the leading edge) to evaluate the effect of a "balanced" rudder.

Then I plan to fair the "balanced" one with a 14" chord to a NACA foil #14 shape. 

My only concern is that the NACA #14 shape combined with the 14" chord might eliminate weather helm altogether and that would be too much of a good thing.

If that happens, I will simply fair the one with the 12" chord to the NACA #14 shape which is a proven performance enhancement.

A while back, Doug sent me patterns for the NACA foil #14 shape for a 14" chord and now Mark is sending me a stock rudder blade for my shade tree engineering experiment.

Thanks to Doug and Mark, I have what I need to complete this project.

This is a great community of Com Pac sailors.

Dave (Pacman)

[Bob23]

Dave:
   Like I said, I'll be following your results with interest.
   On the 23, I can say the 0014 did not eliminate all the weather helm. I don't know how the 16 will perform.
   If you need any of my construction photos, search here or pm me and I'll email 'em.
Best,
Bob23
(Love the reference to "fair and balanced". It's good to know it's achievable with a rudder. Sorry, guys...couldn't resist. I'll stop now.)

[Mark F.]

Pacman:

You're welcome.  I'm glad I could help.  You should receive the rudder on Monday.  The Ida Sailor rudder made a huge difference on my boat.  Your experimental approach looks to be sound.  You've got a stock rudder to compare to your modified rudders.   

We had a nice sail on the St. Johns River this afternoon.  Winds were 13 knots for the first couple of hours and died down to around 7 knots.  The boat makes good speed in the lighter winds with my new Doyle-Ploch sails. I tied line into both sets of reef points so that it will be easier to reef if the winds kick up unexpectedly. 

Mark