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Rudder Fairing to NACA 0012

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WK 727
1st Mate

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USA
72 Posts

Initially Posted - 12/28/2018 : 23:40:55

I noticed that my rudder has a tendency to have turbulence/chatter/poor performance almost all the time and decided to check the profile. Everything pointed to a NACA 0012 profile that has a thickness of 12% of the cord at 30% back from the leading edge. This is ideal for a 3-6 knot speed.

I built templates for every 3 inches and was surprised at what I found. The port side of the rudder was basically flat and the starboard side was about a 0009 profile (this is well known to have a quick stall point). You can see in the images that the port side had a massive amount of fairing compound added and the starboard side had less and also had a reduction of gel coat all the way into the fiberglass to achieve the NACA profile.

An entire container of West System fairing filler was used for the job (that's how much build up was required). The pictures really don't show how far off the profile was. I think the stock rudder is a great place to start, but definitely is not tuned and needs a little TLC to perform. There is no way the stock profile can perform optimally with a laminar flow. Can't wait till summer to see if it produces the results I expect.

Regards, John
Westlawn Institute graduate
Yacht Design and Naval Architecture
04 Catalina 250 WK
Standard rig w/wheel steering
Yanmar 9hp diesel

Steve Milby
Past Commodore

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5851 Posts

Response Posted - 12/29/2018 : 06:54:32

Good catch! Not many would have noticed that turbulence or known what to do about it. I don't remember a C250 owner complaining about an out-of-specs rudder, so we can hope yours was an uncommon anomaly. Correcting it will make your boat perform much better. If others have the same problem, can you show them how to make the templates?

Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore

TakeFive
Master Marine Consultant

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2269 Posts

Response Posted - 12/29/2018 : 07:24:28

quote:
Originally posted by Steve Milby

Good catch! Not many would have noticed that turbulence or known what to do about it. I don't remember a C250 owner complaining about an out-of-specs rudder, so we can hope yours was an uncommon anomaly. Correcting it will make your boat perform much better. If others have the same problem, can you show them how to make the templates?

My 3rd generation rudder (purchased by PO mid-2009 as a replacement) had exactly the same defect, with severe flatness on the port side. I used it anyway because it came with the boat, and never noticed any severe turbulence, but I wasn't racing it. It always bothered me that Catalina would put out a rudder that was so severely asymmetrical on the two sides. I don't really know anything about NACA specs, but the defect would be obvious to anyone who looked for symmetry in the profile.

I recall one other person here about 10 years ago who sent his 3rd generation rudder back to Catalina for the same reason and went with a 3rd party rudder instead. You'd have to search for it - maybe it was Steve/piseas in Newport Beach? Based on the timing of when he did his return (and when my boat's previous owner bought the rudder), I always wondered if Catalina turned around and re-sold the same rudder to my PO. But now it appears that it was not a one-off defect, but perhaps a defective mold (or lay-up plan) that may have led to lots of defective rudders.

Rick S., Swarthmore, PA
PO of Take Five, 1998 Catalina 250WK #348 (relocated to Baltimore's Inner Harbor)
New owner of 2001 Catalina 34MkII #1535 Breakin' Away (at Rock Hall Landing Marina)

Edited by - TakeFive on 12/29/2018 08:46:11

Russ.Johnson
Commodore

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833 Posts

Response Posted - 01/09/2019 : 00:42:54

John,

This is an interesting topic.
I have to be honest, I've never thought about rudder shape.
How did you conclude 12% is ideal for 3-6 kts?
It's not that I doubt you, it's just I don't know enough about the topic to comment.

Here's a link to Wikipedia with what I found.
https://en.m.wikipedia.org/wiki/NACA_airfoil

Off topic, your photo is a 3rd generation rudder for a winged-keel.
The water-ballast rudder is shorter and has worst performance.
There is a whole series of discussions about the rudder changes over the years.
Your post may help clarify rudder issues.

Russ Johnson
2005 C250WB Hull 793

WK 727
1st Mate

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USA
72 Posts

Response Posted - 01/09/2019 : 08:39:54

Russ, great question. I explained what, but didn�t go into why. There are many previous posts that discuss how mast rake and static weight distribution impact the sudden weather helm the C250 is known for. There are many posts about the different rudders produced for the C-250 over the years (depth, width, style). But we never really discuss the impact of the rudder profile and the fact that if it loses its bite then the control is gone and weather helm happens. So my journey of evaluating the rudder began over a year ago. Like many others, my generation 3 rudder had the crack on the leading edge near the pintles and didn�t have confidence in it. I completely removed all gelcoat from the rudder and did a full inspection. If you go back last year I did a post on this topic with images of the bare rudder.

Factory rudder Observations
The form used for the rudder appears to be two fiberglass molds assembled like a clam shell. The trailing edge of the rudder had about a 1/16� gap and wasn�t bonded together with fiberglass. A sliver of internal foam was visible the entire length. The bottom of the rudder had an oval shaped gap where the foam had been shaved smooth with the fiberglass mold. The top of the rudder had an oval shape gap that was much larger and filled with foam. An uneducated guess is that the foam was poured in from the top and would fill the cavity and then expand out the top and bottom. The leading edge of the rudder had one side of the fiberglass including the leading edge like a �C� shape and the other side matched up to it. The gap was large (1/2�) and filled with gelcoat. Ironically the gelcoat didn�t hold up structurally and cracks. I removed the gelcoat and filled with fiberglass strands and epoxy. The leading edge was wrapped in fiberglass to encapsulate the rudder. During this process I checked the profile and noticed how flat one side was molded. At this point, the rudder was gelcoated and placed back on the boat.

Sailing Season Evaluation
I spent the entire sailing season evaluating the rudder performance. I sail with many friends and they enjoy having the helm and adjusting the sails. So I am usually free to observe the action of the boat and watched the rudder. The first observation is that most individuals oversteer the wheel and the rudder doesn�t smoothly transition the change. The reasons are (1) the wheel only has a range of 180 degrees because of the lever arm and lack of a quadrant (which is another project that is underway) and (2) the rudder is pretty flat and water would gurgle with turbulent flow IMHO. The result was that the rudder didn�t hold as well as I want when heeling and driving the boat forward on a line.

Why NACA 0012?
Maybe these Catalina specific links help. Go to Catalina Direct and search rudder. The C-22, C-25 and the C-250 all have a performance rudder that reference the NACA 0012 which is not eligible for class racing. From there, I researched aftermarket performance rudder and saw the same result. The search continued to one class racing forums discussing fairing the rudders. As an example, the J-22 class rules allows a 13% thickness to the chord length. Back to our manufacturer. Rudder Craft makes performance rudders for the Capri line (our flagship for performance). These rudders conform to NACA 0012 on the website. Every article read seemed to support the flaws encountered with the factory rudder on the C-250. So, that is why I chose the 12% thickness to chord length profile of the NACA 0012.

The strength added last season seems to be more that the boat needs and having a factory fiberglass and foam core is what I really want to keep. Fairing the rudder was a fun off-season project over a few nights and was relatively inexpensive. At the end of the day, why not do it?

Regards, John
Westlawn Institute graduate
Yacht Design and Naval Architecture
04 Catalina 250 WK
Standard rig w/wheel steering
Yanmar 9hp diesel

Edited by - WK 727 on 01/09/2019 18:32:11

Russ.Johnson
Commodore

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USA
833 Posts

Response Posted - 01/09/2019 : 16:22:14

John,

Thank you for the explanation.

Russ

Russ Johnson
2005 C250WB Hull 793

glivs
Admiral

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USA
822 Posts

Response Posted - 01/10/2019 : 06:53:10

Russ...Mainsheet article? I'm only one voice but to me an interesting topic.

Gerry & Leslie; Malletts Bay, VT
"Great Escape" 1989 C-25 SR/WK #5972

Russ.Johnson
Commodore

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USA
833 Posts

Response Posted - 01/11/2019 : 12:31:43

Gerry,

Good point. I will follow-up.
Here's a link to the Catalina Direct C250 Rudder page.
https://www.catalinadirect.com/index.cfm/category/686/rudders.cfm

As John described, the replacement rudders use the NACA 0012 profile.
They have both Fiberglass and HDPE rudders available.
Regarding the note about class rules:
"Since these rudders are not original equipment and are a more advanced shape, they are not legal for class racing.".
This is a disclaimer from the manufacturer, which is important for strict one-design classes (Capri-25).

In the case of the C250, it is not one-design boat.
For PHRF racing, the rudder can be "declared" as not OEM and raced "as equipped" or "as sailed".
It is then up to the race officials to adjust the handicap (probably no adjustment).
Keep in mind the PHRF format "assumes" a 155% jib as the default, which no one uses on a C250 anyway.

If you are racing against another C250 in your local club, then you can use the OEM rudder or give the other guy a few handicap points.
It's always been hard to compare racing a winged-keel to a water-ballast anyway.

To summarize, John's post offers improved performance.
Fairing the rudder is good project and a whole lot cheaper than spending $1,000 on a new rudder.
If anyone is racing another C250 at your local club, declare the fairing.
For good sportsmanship, offer to help the other C250 owner fair their rudder too.
Two faster C250's is a good thing.

Russ

Russ Johnson
2005 C250WB Hull 793

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