rudder modification

[Ken Juul]

I've got the tech notes and diagram with fuzzy numbers.  Read all the posts.  Does anyone have the length of wing keel rudder?  Can I cut the extension out of a 4' section of plywood or do I need a full sheet?  Plan to do the cutting and fitting at the boat, but need to shop closer to home.

[Ron Hill]

Ken : If you look in the Mainsheet Tech notes, I published an overlay of the standard and elliptical rudders for the wing keel.  It has the dimension's listed.
BTW, I'm wondering why you want to use plywood?  I wouldn't and didn't when I modified mine.  I used mat and glass.  You might want to re look at my article in the Nov 2004 Mainsheet on "Rudder Modification".  The article also has 4 pictures in stages.  Plywood can pick up moisture - glass can't!!   A thought.   

[Ken Juul]

HI Ron,

I have both the articles.  Just can't read the numbers.  My thought was to use the plywood as the core of the extension.  Of course it will be fully covered by fabric and resin.  Since there will be no holes drilled for fittings etc like on the deck I didn't think moisture intrusion would be a problem.

Is my logic flawed?

[Ron Hill]

Ken : There are a number of reasons that I didn't use plywood.  Some are listed below:
1.   I suspected that the thickness of 1/4" plywood is too thick!!  By the time you overlay with mat and glass (numerous) times and sand it down you won't have a taper that wouldn't expose the plywood on the trailing edge!! - I'd guess.
2.  The pressure on the trailing end of the rudder is the greatest.  I didn't think that thin plywood would be as strong as mat/glass.

To answer your original question, a 4 foot piece of plywood will be adequate for the task.

I don't want to discourage you and think you ought to try your plywood idea.  You're an engineer, let us know how it comes out.  I'm sure there are more ways to do a modification than "Ron's Way".       

[Bruce Hanson]

Hello Ken: Another approach is to use epoxy resin over glass cloth. This combination is stronger and slightly more flexable per the marina guys. You could build the extension with a sharp V shaped attach point at home then epoxy it onto your rudder at the marina or better yet take the rudder home where the environment can be controlled. The temperature and humidity are critical for all composite repairs regardless of the product used. Cost of material would be higher however considering the application it would be worth the expense.

[Ted Pounds]

Bruce brings up an improtant point.  You do NOT want to use polyester resin for modifications or repairs.  It does not have adequate adhesion to old, cured resin.  Epoxy is the only way to go.  W.E.S.T. is the big name on the market though there are others that are probably just as good.  I like the nice dispenser pumps that W.E.S.T. uses.  Your choice of core material is probably not too  important.  Plywood might be easy to work with.  At least two coats of cloth and epoxy and it should be sealed up just fine.   

[Ken Juul]

Are you saying the whole modification should be done in epoxy or just bonding the new piece to the old rudder? 

Assuming you just mean the initial bonding, I have read that Vinylester resin is preferred over polyester resin for repairs to older fiberglass.  But the book I was reading was discussing crack/small hole repair.  Since this is such a large area will the polyester provide sufficient bond?

[Ted Pounds]

I'm saying you should do the whole modification in epoxy resin.  I don't know about vylester resin.  But I do know epoxy will do a great job and is readily available from Defender, West Matine, etc. 

To quote Nigel Calder: "Note that polyester resin is normally used on fiberglass because it does the job and is relatively CHEAP.  Various epoxies, however, will provide a BETTER BOND to old fiberglass, and make a STRONGER and MORE FLEXIBLE repair."  (emphasis mine)

With the total cost of materials for a job like this being less than $100 for epoxy based materials, and with the rudder being a critical component, I'd say you'd be penny-wise and pound-foolish to use anything but epoxy.  Just a few thoughts... 

[Ron Hill]

Guys : There will be a short Mainsheet article and picture in an upcoming issue about my rudder mod. - 2 seasons later.  Sent it in in early December.  Basically it looks just like the day I finished it.  No plywood or epoxy was used. 
A thought.   

[Bruce Hanson]

As kind of a offshoot to Ken's original question does anyone know if epoxies require different paint primers than polyester resins? This winters project is our rudder's water injestion problem. I have routed out several large areas to inspect and fill, there was little if any corrosion, only damage caused by freezing. I have sanded the entire rudder which now needs paint, we ultimetly want VC17 on the whole bottom but for now only want to do the rudder. I wiil hit the paint guys at Strickly Sail but there is nothing  like hearing someones good or bad experiences.

[Ken Juul]

Finally got the rudder measurements.  I'll post in a separate message so they are easy to find.  I didn't realize that the trailing edge was only 3/16" wide.  Think I'll go with Ron's  suggestion of using a couple layers of impregnated cloth as the extension piece.

[Ron Hill]

Ken : Here's color picture of my rudder 2 seasons later.  The Mainsheet article with it's black & white doesn't do it justice.  It's had some hard sailing in those 2 years and appears to be the same as I made it. 

If it'd heavier, we don't notice it.  Backs better with more control at slower speeds and the uncontrolable round up is GONE.  Simply - you have more rudder!!!.   

[Phil Spicer]

Ron,
I never told you how good your rudder mod looks. It looks like factory ! Fantastic job.