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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

New Rudder? Can I build it?

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sodonnell
1st Mate

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76 Posts

Initially Posted - 09/04/2005 : 09:55:27

It seems like I'm always fighting the rudder on my 1980 C25.
It doesn't have the easy feeling to it that I've experience on other boats of the same size.
Granted, the other boats were J-boats that I race on. I'd expect them to probably be better tuned than my old boat.

Anyway, I'm looking at a tech tip on this site about a "balanced" rudder design.

Can anyone give me advise on how to properly construct a new rudder.
What type of wood, etc.
I'm thinking about this being a good off-season project.

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 09/04/2005 : 11:05:09

>"I'm always fighting the rudder on my 1980 C25."

I have a "Mark I" too and haven't experienced what I'd call a radical lee, weather or otherwise 'heavy' helm when the sails are set and trimmed properly.

I suggest doing some experimentation trimming and tuning your rig. If your rig is balanced for the breeze you should track along very nicely with a slight weather helm and an easy hand on the tiller. First thing I'd check... how's the mast plumb fore/aft?

That said, the stock rudder is about as hydrodynamic as a brick... and there's certainly room for improvement there. Have pondered the same project myself... not due to heavy helm, but for the performance improvement.

Edited by - on

Sloop Smitten
Master Marine Consultant

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USA
1181 Posts

Response Posted - 09/05/2005 : 13:38:16

From the C25 Technical Tips.
http://www.catalina25-250.org/tech/tech25/pictures/brudder3.gif

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tinob
Master Marine Consultant

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USA
1883 Posts

Response Posted - 09/05/2005 : 17:18:42

Well this will be a good test of a failing memory but I seem to remember a fellow named Eric Werkowitz(sp) who built a rudder to the specs that you posted. Archives probably has his post. Haven't heard from him on the forum for some time though. Perhaps he'll respond.

Val on Calista # 3936

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thaind
Navigator

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Canada
145 Posts

Response Posted - 09/05/2005 : 21:30:09

Making a new balanced rudder is not difficult.
There is a lot of information on this site.

http://www.catalina25-250.org/tech/tech25/pictures/bsrudder.gif

I made mine for under $100. I have the plan drawn up on DXF and SKD format and if you have access to an E size plotter you can print a pattern full size. The only problem I found with the plan is that since the leading edge is forward it is harder to clear of weed with a boat hook.

Edited by - on

eric.werkowitz
Captain

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USA
283 Posts

Response Posted - 09/05/2005 : 23:55:58

Val's memory isn't failing at all. He even spelled my name right! See this thread.

http://www.catalina25-250.org/forum/topic.asp?TOPIC_ID=8854&SearchTerms=rudder

I posted some lessons learned from my experience after my old blade rudder snapped during a sail with some friends.

Read up on vacuum bagging. If you can make or borrow a rig for doing it, you'll save a lot of time and gt a better product. You can lay up the glass with out it, but it will take longer. This is a good winter project as it will take severla weeks to build. Mine is still going strong after about 5 years.

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 09/06/2005 : 11:47:01

An unbalanced rudder can induce a weatherhelm-like feel on the tiller due to the lifting force generated by the rudder being well aft of the rudder's pivot point. This rudder induced weatherhelm can contribute to true weatherhelm.

(edited due to poor grammar

)

Edited by - dlucier on 09/06/2005 13:30:17

GeorgeB
1st Mate

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90 Posts

Response Posted - 09/06/2005 : 19:14:26

Scott

Yes you can definately build a balanced rudder. I did using the instructions that I picked up on this web site. I used exterior grade ply wood and epoxy. I found a site that specified the cords for a NACA foil of the proper dimensions. I used a router to cut my core to the desired depths, belt sanded to final shape. I faired it with epoxy filler, and glassed it over using zebra cloth with the carbon fiber running vertically. I built up with glass until I reached My final dimensions. Much better than the old rudder ever was. Boat will balance and stay on course with little effort.
Its not a class legal solution, but that is not important to me.

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ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 09/06/2005 : 20:28:37

Build it... and they will come.

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sodonnell
1st Mate

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76 Posts

Response Posted - 09/09/2005 : 13:19:36

I'm getting ready to go purchase materials.

Can someone give me an easy to understand explanation of NACA Airfoils. Based on what I've been reading about rudder design, I need follow some rules on thickness, etc, to get the best performance out of this.

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Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 09/09/2005 : 13:48:16

I don't even remember the acronym but basically it is a shape that is an optimum lifting foil. We obviously do not want a flat rudder even though rudders were flat for thousands of years. If you want to see examples go look at J-boat keels and rudders. The Catalina 25 fin is not NACA.
[url="http://www.boat-links.com/foilfaq.html"]go here[/url]
[url="http://www.caliberyacht.com/Features_Performance_Detail_NACA.htm"]and here[/url]

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sodonnell
1st Mate

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76 Posts

Response Posted - 09/09/2005 : 16:06:54

Thanks for the reply.
The information becoming more understandable the more I Re-read it.

So I guess the only questionsI have left is what section to choose. It appears that a 0012 is a common one for moderate sized boats.

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eric.werkowitz
Captain

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USA
283 Posts

Response Posted - 09/09/2005 : 18:13:29

Scott,

Given the desired max thickness is 1.5 inches, and the width of the immersed part of the rudder is 16-17 inches, I think you'll find the right NACA (National Advisory Committee for Aeronautics: the predecessor to NASA)foil to be 0009. The last two digits in the foil designator are the ratio of the thickness to the chord (width) of the foil. At least that is what I used for mine.

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sodonnell
1st Mate

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76 Posts

Response Posted - 09/09/2005 : 19:39:58

Eric,

Thank you very much.
I have everything I need. Off to Home Depot!

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 09/09/2005 : 23:08:02

I'd be tempted to go all the way up to NACA0012 or NACA0013, and not get hung up on the 1-1/2" maximum thickness. I think the thicker NACA00xx shape would be less prone to stalling, and would produce more windward lift. I don't think it would add as much drag as its increase in frontal area might seem to imply. But I'm not a naval architect, so don't go and do anything rash based on my word alone.

By the way, the swing keel appears to have a NACA-like cross section. You might want to calculate the ratio on one to see what Catalina's thinking might have been. Remember to take into account the angle of the dangle with the keel all the way down when making the fore-aft measurement. (Measure parallel to the waterline, not the shortest distance between leading to traililng edges.)

-- Leon Sisson

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eric.werkowitz
Captain

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USA
283 Posts

Response Posted - 09/10/2005 : 23:45:56

The 0009 profile of the rudder I built has been less prone to stalling then the old blade rudder (which is closer to a 0012.) It also seems to result in less weather helm, but that may really be because I trim sails better now.

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GeorgeB
1st Mate

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90 Posts

Response Posted - 09/11/2005 : 20:54:30

Here is anothe site to generate foil profiles http://directory.boatdesign.net/detail/317.htm

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JaimeZX
1st Mate

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USA
34 Posts

Response Posted - 09/12/2005 : 09:40:41

For whatever its worth, my friend and I built a new rudder for my Hobie last spring when the old one snapped off. We just used foam and fiberglass (foam being easier to shape than wood). It's quite light and strong. I have a detailed writeup with photographs on my website. You could probably adapt the process to a Catalina rudder fairly easily. :) I think it's "part 3" under the Hobie 16 section.

Edited by - JaimeZX on 09/12/2005 09:41:52

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.