Help with CSK cat rudder design

Recommended Posts



I have been scouring the forums for info on rudders and have come up with a lot of great stuff.  My questions are mostly about the best/most efficient way for me to make new rudders using what I have.  

I am refitting a 1975 CSK Polycon cat and need to make new rudders.  Old ones were trashed and are gone but I have paper tracing of the original shape.  They are transom hung with tillers and crossbar.  I would like them to kick and want to use existing stainless steel mounting hardware with modification as necessary.  I would hold them down with sacrificial dowels.  No sure what to do the build out of.  I have old growth 1/2" planks of nice doug fir that came with boat for this purpose so would be nice to use what I already have but also thinking about foam core/composite build although.  

Original rudder pic, the original design dimensions, what I am thinking for new design and a pic of the hardware. 

CCI (Phils foils) quoted more than 5K and no kick up design, so not so thrilled with that option. 


Questions are: 

- Is this a feasible design or are the loads too much and should I just stick with non kick up rudders?  How much should I extend the SS cheek plates aft to provide more support if kick up?  How should this be done? Welding, composites? 

- What NACA section should I select.  Is 12% the standard or should I go lower for more performance/lighter multihull? 

- What core material/layup schedule? 


Thoughts, criticisms and any suggestions are most appreciated. 



Displaying image001.pngRudder original.jpgruder harware plate.jpgrudder swing up concept.jpg





Share this post

Link to post
Share on other sites

answers in no particular order many to questions you haven't asked:

1. Even if you want to build it yourself pay someone to design it.  Any advise you get on laminates etc for free will be worth what you pay.

2. Cool kids use Eppler 836 foils instead of Naca these days.

3. Don't go below 12% unless you have a really good reason, particularly on a rudder.

4. Home built kick up rudders are a nightmare.  If you don't have a really solid lock down mechanism (no a pull down rope won't do it) the rudders will raise slightly and loads will go through the roof.  if you want to retract your rudders go with a dagger style.

5. pics don't work for me either.

Share this post

Link to post
Share on other sites

Thank you for the suggestions.  Very happy to pay for design on this, given my lack of expertise and how critical the rudders are.   Any suggestions on who? I have not had much luck in with the people I have approached so far.... 

Ok trying to post pictures again... Not sure whats wrong, I see them when logged in on the thread but not there when I'm not logged in...



Rudder pic1.PNG

hardware overlay.jpg

Rudder original.jpg

Hardware  measurements.jpg

Rudder idea 1.JPG

rudder idea 2.JPG

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now