rudder dimensions

[craigyw]

Hello there
I am shortly to become the owner of N3237 .  (collect her after my holidays near end of this month)   I am interested in making a foam/carbon rudder as per the technical section of this site, which is brilliant by the way  big thanks to those who take time to create these articles.  
I know as the boat is old the gains will be insignificant using carbon but it's more to do with the enjoyment and gratification of building one myself, as I would never dream of spending that kind of cash to buy new!!  Oh and I am working on the waistline also!
Anyways..... does anyone have the dimensions or a profile plan of making a rudder.  (lifting type)  I would be very grateful.  or could tell me how to do it in idiots terminology .
I can visualise the use of a router creating depth in the foam and then shaping, but what are the depths??
I had a look at "Profili" as suggested but all this computer wizadry is just withchcraft to me I much prefer something on paper. 
Sorry that my first posting is just a bunch of demands!!!   and more to come re vacuum bagging! 

Regards to all,   may meet some of you at the more northwesterly events -Craig

[grazz]

Profili is good for printing out the the section profiles, it's not too tricky use once you get the hand off it. Most rudders are NACA0012 which is a standard profile in Profili. You simply choose the section (NACA0012), specify the chord (rudder width) and how thick your skin will be (somewhere between 0.5mm and 1mm depending on how many layers of carbon you add). You can then print out the sections, place them in the right position along the length of your rudder and measure the depths from the print out.

There are loads of rudder shapes around,  ours is quite small with a simple curve on the trailing edge and a small curve on the leading edge (roughly 10mm over the length), the dimensions are:
Length (below water line) 750mm
Chord at water line 185mm
Chord at mid section 175mm
Chord at tip 130mm 

Hope this helps
Enjoy the building

 Graham

[craigyw]

Thats a huge help Graham  thank you ever so much.  started to get the stuff together now.

[Mike Storey]

Slightly related to this thread, can anyone advise the dimensions of the restriction on horizontal foil size as proposed (and passed I think) at the AGM.
Cheers Mike
N3491

[Jeremy C]

Mike:
Max width 1500mm, max 'depth' (all when looked at in vertical plan view) 600mm (box rule in effect.)
This is not the absolute wording but interpretation of it...

[craigyw]

Eureka!!!
just printed off my foil profiles in Profili and now I can get to work on shaping the core.  Brilliant.

thanks again to Graham for his advice.  It was all the thinking I was doing that was making the process seem hard.  But the reality was much simpler. 

[Biniou]

1500 mm of width for wings rudder, that's impressive!
Is there many wings rudder with a such size? Where can we see pictures?
But, if there is any interest to make it wider, why this limitation?

[John Meadowcroft]

The limitation was proposed on the grounds of practicality and no one involved at the AGM knew of an existing rudder being used on a N12 that would not comply with the rule.  Gavin Willis claimed to be using the largest rudder wing, and no-one contested this!  He suggested that sailing in big waves with such a large piece of kit was "interesting" and that he would be amused to watch anyone try with a larger one.  Gavin seems to have found that the practical limit is actually smaller than has been found.  However, given that first time round with T-foils in the 1990s, the conclusion was that they did not work, he could be wrong.

I disagree with limitations, but there are bigger things to worry about.

John

[Biniou]

T-foils did not work in the 90s...But twenty years later, do they finally work? We still speak about them, even when there are bigger things to worry about ( I'm new, please, tell us what they are!)

[moomin]

Surely there's an easy answer if you want more T foil but still comply with the box rule,  Twin foils, in a bi-plane type arrangement at different depths on the rudder blade! 

[Jeremy C]

so one of these then?!!!

[moomin]

There really is no such thing as an original idea is there!  Though I was imagining the 2 foils much closer together just below the water line, so that they are a similar distance from the pivot point.  In that arrangement does the angle of attack change more for the bottom foil than the top given the relative distance from the pivot in the rudder stock.  More like this:
http://www.wired.co.uk/news/archive/2012-03/20/mit-sound-barrier-biplane

[angus]

Hmmm there seemed to be a few shock waves at Hayling Island.

[Biniou]

Every pictures I have seen showed wings very far from 1500 mm8)