Subject: Re: [harryproa] Rudder build method?
From: Gardner Pomper
Date: 3/28/2010, 2:09 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Hi,


Thanks for the reply, but I am, as always, a bit dense on understanding it. I looked up the NACA foils on wikipedia, and I think I now understand what a NACA 0012 16" chord looks like, and I have a formula from which I can derive the position of maximum thickness, which is (I assume) where I would place the shaft. I do have construction questions, though.

Are you saying that you are making your rudder out of 1 piece and bending it, or 2 pieces and joining it?

Are you carving foam and glassing over it, or making a flat panel?

You say you are getting the right radius from 1 layer of double bias. That sounds like you are making it flat, without a core, but you then mention that you are using 10mm foam. So are you using 10mm foam, glassed on just 1 side and slitting the foam before bending? Or are you using 10mm foam for the sides and just 1 layer of glass for the leading edge that gets bent?

I tried googling "sheer web" but I don't get any results that seem to have to do with boat construction. Is that a method of attaching the shaft to the rudder?

I can wait for pictures to build, but I may need to order some materials. I was going to order some 3/8" (10mm) corecell for beams and a kayak, so I was planning on using the same for the rudder. Since my plywood proa is only 20' long, and your 16" chord is for your 50', I am assuming I should use something like a 10" chord??

I keep trying to tell myself that there may be lurkers here as ignorant as myself, for which my dumb questions can do some good and that they are not exclusively annoying. If not, just say so and I will send private emails.

- Gardner
York, PA

On Sun, Mar 28, 2010 at 12:23 AM, Rob Denney <harryproa@gmail.com> wrote:
 

I am getting the right radius for a NACA 0012 16" chord from one layer of 400 double bias.  You should manage with 200 plain weave.  Suggest you don't glass the interior until you are ready to close it up, then add a couple of extra layers to the nopse section and an inner skin to the core.  I use 10mm foam glassed on the outside and it conforms to the aft sectionof said foil.    Unless the ply is very thin, I would cut slits in it pre bending.  A sheer web at max thickness (I have a shaft) gives the sheet something to bend around. Glass only ahead of the web.   I totally screwed up my first one, should have the second attempt ready this week, will post some pics.  If you really want to get stuck into it, let me know what is unclear in the above.  


rob


On Sun, Mar 28, 2010 at 1:00 AM, Gardner Pomper <gardner@networknow.org> wrote:
 

Hi,


I was wondering what the current "best practice" idea is for building a simple rudder (I need to build 2 for my plywood proa, from last year). I was considering trying to make it as one panel, with no core material at the leading edge and bending the fiberglass 180 degrees, but the practice piece I made seemed like that was too much of a bend for the fiberglass. It seemed like it wanted to delaminate, because the outer layers had to be longer than the inner layers to make the curve.

My next idea was to build the rudder in two halves, using Derek Kelsall's deck edge radius type scheme and glue the 2 halves together, but I wasn't sure of being able to make a good bond on the inside of the curve.

Finally, I guess I could just carve foam, and layup the fiberglass over it and then vacuum bag it.

What is the current thinking? I would like something pretty simple, and it doesn't need to last long, but I would like to get it done soon so that I can try out the proa sailing this summer.

Thanks,
- Gardner



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