Steering a dinghy sailing backwards always feels realy positive with only a small movement being needed to steer the boat. I’ve more or less given up on sail steering on my cat but i dont particualy want to remove the nice skegs from the back. Ive been wondering wether it would work if i fitted a small rudder to the forward beam. If its more positive that means that i would get away with less movement, and therfore less drag in tacks right? Or atleast i could use a smaller single rudder blade without it losing grip at low speeds.
So if you have a fixed foil(skeg) aft and rotating foil forward will it be beneficial,right?
The old rule of thumb used to be that you want weather helm so that the rudder develops a positive angle attack; the fact is that weather helm is NOT necessary for the rudder to develop a positive angle of attack. The boat is in essence drifting sideways a small amount so if the rudder is neutral AND the boat is going to weather both foils-the keel and rudder or the forward rudder and skeg in your case are at the same angle of attack to the water and at 0 degrees angle of incidence. This is a low drag way to sail to weather. Weather helm helps if you don’t want to concentrate too hard since if you let go of the tiller(stick) the boat will round up–a good ,safe characteristic.
With a forward rudder and a fixed aft foil you can’t have weather helm: if the boat was balanced so that you had weather helm then the forward rudder would have to be sailed upwind at a negative angle of incidence! Thats slow for upwind vmg.
If the boat was balanced so that the aft foil was quite small and the forward rudder(turnable daggerboard?) much larger AND the boat had neutral helm then you would be at least as fast as a normally configured boat that was turning the rear foil and because you have more area doing the turning tacks should be quicker-if the sideways movement of the hull was not too great.
But why not use twin rudders as in a CBTF arrangement: they allow an infinitely controllable balance coupled with collective control of the angle of incidence on both foils upwind so you can dial out leeway all together which is a huge upwind drag reduction and the proper placement of the twin rudder leads to a reduction in wavemaking drag. And since it’s on a cat(right?) you don’t need a canting keel. And you just made your cat point better and turn faster than any cat I’ve yet seen! Of course theres always a negative: how in the hell do you retract the foils in the windward hull?
I was thinking of having a single rudder on the centerline right up front on the forward beam. I think it would be hard to fly a hull on this boat as the center of effort is so low with the twin rigs, I haven’t got it to heel much at all so far in up to 15knot winds. As to the weather helm problem making much difference, it sails to weather with no rudder anyway (it just dont tack without going backwards for a bit!). Twin foils is interesting though, if I kept both on the centerline and ditched the skegs, then the retracting problem is no more. I can see twin foils working downwind too as you could use it to induce an apperent wind forward of the beam. I would have thought that using the foils to crab away from the true wind would allow you to sail effectively deeper without losing your apparent.
Hey, Matthew: I think you hit on something with the twin foils going downwind using a negative crab angle!You would DEFINITELY improve vmg downwind . You couldn’t do the same thing on a CBTF boat because the canting keel would then develop induced drag but on a level boat downwind with just two foils you’ve got something…
Matthew, is that you on the trap? What boat?
Doug Lord microsail.com monofoiler.com
High Technology Sailing/Racing
Right oh then I’ll be doing some modifications to the cat in the next couple of weeks! Yes the pic is of me sailling my Rs 600. Its regarded over here as just about the hardest singlehander to sail, as it is VERY unstable and pretty quick (we were clocked sailing at around 25knots on a beam reach one windy open!) Its one of a range of boats produced by a company called LDC, which are hugely popular over here. Take a look at; www.ldcracingsailboats.co.uk
I used to sail a little 22" monohull back in high school. I tested it with a regular rudder and a bow rudder. The bow rudder seemed to make the boat point higher and turn faster. It did seem to have a little tendancy to “wander”. I never took the time really adjust to see if it was possible to overcome this issue.
I am planning on adding it to the list of mods to the “Wildcat Project”. I have one of the 4 channel radios from Hitec, the v-tail mixing should be perfect for coordinating the rudders.
Pure speculation here.
I wonder if it would be possible to have a boat that uses the twin foil concept along with hydrofoils. If say you had a foiler cat on 4 T-foils, 2 of which would be conventional T-foil rudders but the other two would be bow rudders/turnable daggerboards, surely it would be posible to make one hell of a fast boat to windward!
Well, I think the trimaran would still be the better boat for foils because you would only need three foils, have a wider beam and because the outside hulls don’t carry the boat except in the lightest of wind they can each be 1/4 the weight of the main hull.
But the big problem would be:what do you do with foils on the bottom of turning rudders in light air?
So far I think the fastest solution may be retractable foils mounted on the forward single cross beam with just a single rudder. Though if you could turn the forward foils AND retract them then you’d really have something…
I wonder if you could not make a set of folding foils. Imagine if you cut off the bottom half of a rudder. Then split that along the chord, yielding 2 thin foils. If you could cause them to sit at a 90 degree to the foil they would provide lift, if flat against each other it would look like a normal rudder… If you used 2 torque rods to open and close the foils there would be little drag…
Kris, thats an idea; you would reduce hydrofoil wetted surface 50% and thats good;the net gain or loss in rudder or dgr. board area would be-to some extent-made up by the endplate effect when the foil is deployed.On the rudder foil it might be a problem because it should be a symetrical section. Kind of complicated ,maybe, but worth some serious thought…
I cant see that realy matters in a model, as long as the foils are removeable between races. In marginals it would be down to the skippers judgement. If you were to add folding foils all it would do is increase weight and lower marginal wind performance, making the forward foils turn is going to add enough weight as it is. If you were say applying this to an ocean racer maybe it would be good, but then it would have to be bloody reliable to be worth it. My main concern would be making a system to adjust the trim of the foils or a flap that wouldn’t get screwed up by the foil being turned.
Got the boat on the water today with just the bow rudder and original skegs, had a bit of a balance problem, it woulden’t bear away out of a tack for anything. Mind you it was silly winds to be sailing it in, gusting about 25knots, after sailing backwards for a bit it got hit by a big gust and pitchpoled backwards, resulting in a wade to go pull the masts out of the mud! It looked real good when it was going though, just flying a hull and tearing along on a tight reach. Now just gotta build up the corage to hack of the nice carbon skegs and add a rudder at the back too…
Just heard on Multihulls Digest that a Formula 40 “Fluid Design” had forward rudders and aft fixed daggerboards and supposedly did well with them…Still think that fore and aft foils like CBTF with no daggerboard could be real fast…
If not, keep in mind you have a long straight keel (very little - if any - rocker) and the boat will track very straight - meaning it will provide difficulty in tacking/changing direction. The long keel is often added to kayaks used to travel lakes and rivers, while “white-water” boats have no keel and look like a curved banana peel for easy change of direction.
Matt
I owned the fastest mini40 cat in our club for a while. It was built by me using Snapdragon floats. Thye were 850mm outside to outside at the widest section of the boat. I had underslung twin rudders. There was a “t arm” on top of a brass rod that was fixed into the rudders. In each hull I had a servo controlling each rudder. I had steering arms attached to each side of the servo and rudder arms in both sides. The inside arm had more movement than the outsideI.E. the servo arm and the rudder arm have holes in them, if you position the outside arm in hole No5(let’s say) then the inside arm get’s positioned in hole No 3(taken from the pivot point)on the rudder arm. The positioning on the servo arm is the same on both inside and outside. The idea for this is so that when you tack your boat the weather hull turns tighter than the leeward hull creating a faster turn. I had a central “pod” that housed the winch and receiver as well as the mast step. Obviously both servo were connected together and the wiring harness ran from the “pod” to each hull through the beams. This boat sailed really well with .78sm sail area in upto 15knots apparent.
This system worked well in that the boat tacked well in all wind ranges and tacked nearly as quick as tri’s.
I hope you can understand what I mean by all this, if you need some part of it clarified that’s not a problem.
My personal view is that bow rudders should be underslung for better control, if you feel that the ldea of bow rudders works for you.
In my experience I have found that on a whole rudders work better underslung at the stern.
Peter
Dick, the skegs are more like windsurfer fins than say a Dart 18’s skegs. I haven’t cut them off yet, barely touched the boat since october, might do something with it soon though.
Peter; Have you seen my boat;
So far a center rudder seems to work ok, the boat rarely ever flys a hull so it shouldn’t ever come out of the water…
Just tried the cat with both bow and stern rudders, it seems to tack pretty quick, no stalling at all once i had the hang of it. It was very light wind but enough to get going, none of the mono r/cer’s were about so I guess it was too light for them, another good reason for owning a multi! I would have some pics to show but I didn’t have much time on the water…
Matt, how did you set up the servos? Did you have the “collective” type steering available-both rudders turning same direction-as well as both turning opposite directions?
I’m really interested in this and when I get time I’m going to modify the 48" D4Z cat I have to see how it works. I’m thinking that particularly on a cat and maybe on a tri it would really make a difference…I think it will be interesting, in stronger wind, to see if the twin F & A rudders help the boat thru a tack with less speed loss…
Did you have just the fore and aft rudders-no daggerboard?
