tubes for the rudder shaft to enter the boat through… i am using 1/8" interior diameter carbon, but i am running out, and can’t find anyplace that carries exactly that interior size… what are you guys using? i guess i could just drill out something in wood on my press, but that seems a little low tech [heavy too:mad:] lol. anythoughts?
Have you tried on-line kite shops? They carry both tube and rod - but not sure of specific diameter sizes.
Why bother?
It is a very odd obsession of Footy designers that the rudder should be inboard. Why is very hard to see. Very early ‘modern age’ (i.e. post 1950) boats with separate rudders had the rudder stock substantially forward of the after waterline ending. This was found to give very poor control and rudders rapidly migrated aft to the end of the waterline or a little further.
Along comes the Footy. This is a normal(ish) hull sawn off at the after waterline ending. So what do we do with the rudder? Move it fowad under the hull, so that it would ‘look’ right if the boat had a full overhanging counter stern. Actually the visual effect is comical and - predictably - control problems manifest themselves.
Hang the rudder where it belongs - on the transom - unless you have highly devious reasons for doing somethng else.:devil3:
smile… you never know if i have devious reasons… lol.:devil3:
i have thought of that, but even doing that i would still use a tube as the gudgon… [or do you do something different?]
i think it would make a difference, probably in a good way… hmmm, now i have to try it!:rolleyes:
Point is tht if it’s up the outside, doesn’t need to be watertight, water lubricated, clearances not so critical. I sand to fit.
good point. thanks!
one thing though, with a transom mounted rudder, don’t you lose the “endplate” effect? and so you lose some effiancy… i guess, the benefits of having the rudder off the transom cancel out the lose of the endplate effect?:graduate::zbeer:
No, put the ‘balanced’ bi under the counter. That’s the bit where the endplate really matters - on the uphill side of the pressure curve. It aslso helps stop air entrainment.
In my opinion, the main benefit to the transom hung rudder is the longer lever arm it offers(in terms of distance to the fin keel “pivot” point), enhancing turning moment. My Footy’s rudder is inboard, having been built per Brett’s early plans on one of his fiberglass bare hulls. Last fall I was having some difficulty coming about in choppy conditions, so I was considering moving it outboard.
However, since I’ve been experimenting with the MacRig in preparation for the Sheboygan event this spring, I have found that difficulty coming about is no longer an issue. So I have decided to leave it where it is & I suppose my “highly devious reason” is simple laziness. 
But with the longer lever arm the iduced drag from tacking is less. Sometimes laziness prompts us in the right direction.
Let’s not in our haste to promote one over the other lose sight of a potential for “TOO” much rudder movement from longer arms and transom mounted rudders, thereby applying brakes when tacking during heated moments on the course or around the pins!
It was long considered a good idea to use rudders as brakes for multihulls approaching the starting line, rather than dumping jib and then main when a bit too early for the gun. A few “wags” of tiller caused boat to actually dip bows as it stopped, whereas the guys who let out the sheets, had to sheet in and try to trim at the same time as steer through the crowds. I found it much easier to watch and worry about where I was going, than over sheeting when trimming back in and watching sail instead of competition.
With a short, high-tech, space-age, ultra-sleek hulls as found on the footies - keeping up speed seems to be a better payoff than losing time by jambing the rudders over when excited.
my opinion, of course.
Sure - hence my preference for whipstaff steering - and self-discipline
Here is my simple solution to the question for transom hung rudders.
Model aircraft hinges, Lightweight, cheap, self aligning, easy rudder removal and replacement, available from LHS, simple engineering, easy fit.
As Dick rightly points out with a transom hung rudder a longer moment arm means a smaller throw is needed thereby smoothing out control movements and therefore being faster.
There is also some conjecture of a benefit from buoyancy in the ends which I won`t go into here.
As an aeromodeller I cannot help but like that solution Ian.
If you do want to use carbon tube Barrett, the sizes I use are 3mm OD 2mm ID tube with 1.8mm rod as the shaft. This is the closest fit I have come across in these small sizes. I have a good stock of this and other useful small sizes from my kit production. I would be happy to help anyone out with 50cm or 25cm lengths at sensible prices. The 3x2 tube mentioned above and 4x3 is also ideal for Brett’s new rigs. 50cm lengths will ship pretty easy.
Let me know,
Graham
thank you graham. i actually have some aluminum on its way that i think i will try out… we’ll see. but i also may have a go at ian’s hinge idea… i like it!
now, shall we open a new can of worms here? the rudders i see on most footys are probably about 4-5" deep and about 1- 1 1/4" wide at the root… this is not toaking advantage of the entire box in the sense that a long narrow foil will have as much lift, with less drag than a short one… any thoughts on why this seems to be modus operandi?:graduate:
:zbeer:
howzit guys
Just been reading through the threAD, what would the best method for putting rudders on a cat? I’m stuck with this. . . . .
i would say that any of the methods mentioned in this thread would work… once you have the rudders installed, you can either put a pushrod on either side of a steering servo mounted between the two hulls, or, you could try to rig something up where you have a bar tying the two rudders together, and a servo in one hull controlling it… that would be more reminiciant of say a beach cat…:graduate:
My thoughts are as big a lever arm as is consistent with keeping some of the rudder under the hull (avoid air entrainment). Keep rudder size to the minimum (it slows the boat down, not speeds it up). However, ‘minimum’ is influenced by the quality of the hemsman (poorer helmsman, less anticipaion = bigger rudder to correct after things have started to happen), how well balanced the boat is (poor balance = increase rudder size and make the brute work for its living at a low angle of attack), how much it lifts the stern out on heeling (please leave somethng in the water). There is also the little matter that the higher its aspect ratio, the easier the rudder is to stall - which we do not want.
Put all those parameters into my magic pot and what comes out is generally a Footy rudder! The exceptioin is the rudders on the UHPC boats, which are cut down at 45 degrees from the bottom of the transom.
I’m pretty sure the finer details of the planform don’t matter very much. I once read somewhere that the elipitical wing of the Spitfire was one of the minor economic disasters of WW 2 - no detectable improvement n performance over the much squarer wings of the Bf 109 and Fw 190, but much more expensive to make.
does where the rudder pivots, have any thing to do with sensitivity and such?
more forward, and the rudder vanes easier, more back and the rudder has more “grab”. as well as effects on servo load. any other thoughts?
from my understanding you are right on nigel… if you go too far however, the rudder ceases to work properly… as angus was saying above, there is a happy medium… now, we just have to find it…:rolleyes:
The rule of thumb for 1 Meter boats always was 1/3 fore, 2/3 aft of the shaft. Seems to give the best trade-off between boat response and servo loading (not many things worse than a rudder that can’t respond in a blow!).
That might go right out the window with Footy-size rudders, but then again, lots of folks are using micro servos to drive the rudder.