Trimaran Turning Radius: Ama Position

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Trying to better understand the effect of a short distance between the cl of the rudder and cl of the daggerboard and a longer distance on tacking ability. Are you saying the question can't be answered because there are too many other effects?
I presented the question poorly by saying "turning radius", what I was trying to get to is how is turning affected by a short or long distance between the rudder and daggerboard on a trimaran?

Original post with rephrased question:

 

James,I was just referring to the program Doug was using to try and draw the radius as the are limitations as to what you can do with the paint program.

 

One of my points is that the fine bow actually takes over and that the pivot point moves from dagger position to halfway, three quarters-way, maybe all the way to bow - and the combined pivot/bow now acts like a turning dragging brake ... plus your rudder at full turn isn't helping either (this is a lightweight tri, little momentum forward when head to wind).

 

Gary, Thanks for your full discription of going though a tack.
One of the thing I had been wondering has the effect of a deep forefoot on a bow, so it adds to directional stability.

 

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So the dagger position relative to the rudder has little to no effect on turning?
I don't know, Gary: Right or wrong, I've developed my own theories on the subject based on a lot of "real world" experimentation. In the 14 and 20' tris I designed and built my impression was that board position was critical for tacking well. In subsequent RC tri tests the position of the board was very important-if it was too far aft(with both versions properly balanced sailing upwind) the boat would stall in any wind, whereas the same boat- with the board forward- always completed a tack.
It was a revelation to me that a "properly balanced" tri is no guarantee that the boat will tack well. I've learned since then that the board can be placed anywhere you need it to be-for instance a foiler needs the daggerboard quite far forward- which just so happens to improve tacking in a trimaran -in my experience. Balance can be achieved regardless of where the board is by juggling the relative areas of the rudder and daggerboard.
The distance from the rudder to the daggerboard is not the only factor in turning a tri but, in my experience, it is a major factor.


This article is about a cat(or tri flying the main hull?) and specifically discusses the concept of juggling rudder/daggerboard areas to place the daggerboard forward
of its usual position. http://www.aquarius-sail.com/catamarans/arc21/index.htm

 

Gary Baigent summed it up pretty well.
Sorry James for trying to get doug to think about the whole picture as Gary B discribed.
Glider Kilo Papa is a very nice machine, outa my $ league. I will stick to my vintage Ka8b for now.
The relevance of the glider flight if you tell yourself that the wings match the centerboard and the elevator matches the rudder, you get to see/feel the motion of how they work together. Where as some keelers will virtually spin about there keel, multihull typically won't. Hence doing a loop in the glider

 

Doug interesting comment about the boared fwd and then being able to tack.
If it is the relationship of the board to rudder distance, you may well be able to make the balanced version tack by mounting the rudder further aft like the !8ftrs, I14's etc on a frame network

 

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Really?!

 

may be the problem has been the term turning radius, everyone is seeing it in a different way.

 

If the said tri turned about the centerboard the turning circle would be more like this with no other factors considered

 

Gooday all. What can we all learn here ??? Doug - I have found that the farther aft the rudder the better the 'turning' - 'tacking' manouver could be carried out. 1st/ let's say - that I don't 'pivot' a vessel in any manouver - as I've found that to take a vessel through a nice sweeping curve is to keep maximum boat-speed & thus the manouver is carried out faster, smoother & quicker especially having lost less boat-speed.
So - I don't pivot a vessel - mono or multi ! ! The faster the vessel is moving the quicker (better) is the total manouver.
2nd/ I've moved several rudders from under the back of the boat - to either 'transom-hung' or on extensions out the back of the transom & every time this was done - the boat increased it's ability to manouver & go higher to windward -
Oh & they all won more races - which with those boats - was the result the owner was looking for.
'Farther-aft' being from the CoE, CoLR & well behind the hull - ie - in clean water flow area.

Is it possible to consider that the distance between rudder & c/b might have a similar effect - on turning or manouvering - as to a short or long wheel-base motor vehicle - - in which we all notice a great difference in the steering capabilities of different wheel-base length models Yes/no ???

Re - the 'glider loop' thing - 'fng' (oh boy - there are so many things I can do with that name- me thinks you might change it - eh) as Oz/K1's we could - take the micky out of each other - but I'm worried that the rest of the forums would think we were having a deadly hate session - rather than just having a tad bit of fun. Now - back to this 'loopy-thingy' - front bit (nose) down circle - I think I'm beginning to see how that can be related to a multihull turning - especially a light-=weight ocean going tri. By-the-by - I'm also trying to get one of those to go cruising up in SE Asia - so I've a personal vested interest in all these - discussions - taking place with this subject. That arc - turning circle - might be like a easy elongated looping curve - eh ??? What say you all ???

There we are - I've covered some of it. More to come yet - see masts section forums - cause 'blunted' sure did say some interesting things about wing-masts & 'C' class. Ciao, all, james

 

What I'm seeing is leverage,
That is with an aft board you have a short lever (rudder to c/board) turning a long bow.
With the c/board forward you have a long lever turning a short bow. Long lever wins every time.
Just my 2c

 

redrb, yes, also because the stern is pushed outside the circle relative to the centerline the vessel gets through the tack more often than not.
where as the aft board has to push the bow around the raidus typically running out of velocity.
I'm not sold on the aft framed rudder being the answer doug wants, but it will be a gain on the aft board fwd rudder.
Here is the big assumtion ( making an *** outa .... ) if dougs fwd board was fwd of the beam and rig it would definatly aid in tacking.
If It's easy I'll do anothe red line or two.

 

pictures

 

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Well done. Did you do that with paint?