The set up is pretty simple, the stern rudder is about 3 times the area of the bow one as the c of e of the rigs fall about 1/4 of the length of the boat from the stern. They are set on seperate servos, the stern one to the left stick, the bow to the right (I might change that),no daggers. The trick is only to use the big stern rudder when tacking, the bow rudder is used to trim the boat when sailing along. I wish there had been more wind, but the fact it even tacked without stalling in what little wind there was was impressive IMHO, also considering the stern rudder was one I stole off another model and the bow one was a crudely shaped bit of 3mm balsa…
A few years ago I build a model of Tom Blackallers USA ? the twin rudder 12.
Originally I tried sailing with a servo connected to each rudder. When I was sailing carefully by myself I could get it to work (much concentration!). When other boats were around though I would always accidentally tack or crash or hit the mark. D?oh!
I eventually came up with the system shown in the attached file.
The aft rudder was set up with the normal linkages.
The bow rudder used a flexilink connection which passed through a second servo just aft of the bow rudder.
The tiller arm on the bow rudder had a slot cut into it which allowed the connector to slide from side to side depending in the setting for the bow servo.
This meant the boat had two modes. Lift mode where the rudders turned the same way, and Steering mode where the rudders worked in opposite directions.
In Lift mode the boat would crab sideways. It was a really strange thing to see. You could sail along side someone than just slide away. It was cool! In fact there was enough lift coming off the front blade that it would visibly lift the bow when she was sailing fast.
In steering mode the boat spun better than anything I had ever built before. It pivoted on the little center fin and would turn inside other boats.
I tried the same system later on a catamaran but it didn?t seem to work as well. It steered and tracked well but I think the extra drag through tacks slowed it down a bit too much.
Tranth;
I dont think that would work on my cat, theres too big a difference in size between the rudders. I guess that your’s were more or less the same size? You got any pics of the cat you tried it on by chance?
Based on my work with CBTF it seems that the twin foils need to be nearly the same area…
Cool linkage idea Tranth.
Another thing I’ve found is the ease with which a twin foil set up can be done wih a computer radio like the 9c: eliminates linkage between the two altogether.
Matt, did you eliminate the daggerboard?
Doug, this set up isnt really like CBTF, its more like having a big pivoting daggerboard at the back and a small trim tab like rudder at the front. There is no daggerboard between the two, it would be pointless and just cause drag…
Another thought, If I did set thes boat up with rudders as on a cbtf boat they would be so close together towards the back of the boat I doubt it would help tacking much. When the boat went into a tack the whole front of the boat would have one huge lever against the turning force from the rudders, thats not going to be fast in windy wavy conditions. I think that makes sense…
Another little advantage of having a rudder so far fwd is that if I add a T foil to keep the bows up it will be a lifting foil rather than pulling the back of the boat down, thats got to be better surely??
Matt
Be careful using T-foils up forward. Once the bows get depressed a certain angle the forward foil will get a negative angle of attack and drive the bows under. When the foil is at the back, the more the bow goes down the more the foil wll try to counter the nose-diving
Tranth
Forward foils like on the F3 ,X3 and full size Rave are about the most stable form of hydrofoil set up-both in pitch and roll. It is critical that the quarter chord point of each forward hydrofoil is at a point forward of the boats CG such that the forward foils support 80% of the static weight of the boat and an aft T-foil supports 20% of the static weight.
If the fin supporting each hydrofoil is used as lateral resistance then the CLR of the boat will be forward of what is commonly associated as the best rig position on a multihull. No matter since the foils hold the boat rock steady virtually eliminating any chance of pitchpole or capsize and just gets more stable as the wind blows harder. Its important to mention that to have full benefit from the foils they should be equipped with flaps connected to a wand type altitude sensor. More info on this on the multiONE website.
Again, the rig position of a foiler is determined by the load on the foils and generally winds up being considerably farther forward than “normal”. This rig position would not be suitable for a conventional cat or tri. The foil loading described above produces an easy foiling rock steady hydrofoil that is fully automatic with no radio input at all.
One thing that would be cool to try is to turn the outboard foils when the rudder is turned but it gets complicated when you factor in needing to retract the foils in light air…
Note: the foil positions described here will work for a two foil monohull as well.
Well what i was thinking was a wand controlled anti diving foil, though thinking again I’m pretty sure it would just cause more drag and hassle than its worth. I dont think Theres any point making a full on foiler out of this boat, the manovability problems would be solved by rhe foils so there would be no need for having the two rudders.