VECTOR FOIL
Robert,
thanks for directing to Fritz’s latest work. (Garadgast topic) I have not seen the videos of the model before. It certainly appears to work very well. Looks as though the video has been speeded up, and image those breakers scaled up!!
I went to a talk a few years ago from someone who had developed models with hinged vector foils. As I understand, the pivot axle is not level, such that as the foil hinges downwards it increases in pitch, giving more down force. I assume the Proa does not have this?
Though it adds a level of complication the hinged foil has some good points. It does appear to hold the ama down as it comes out of the water. In harbour the foil would lifted, significantly reducing the beam.
cheers
Mark
This thread has been relocated to General Discussion, thanks!
I went to a talk a few years ago from someone who had developed models with hinged vector foils.
Gile Whittaker, by any chance? I tried to contact him when I went to Edinburgh, but got no reply. I haven’t read anything about him going beyond his model experiments.
I think I once saw a picture of a canoe converted into a vector foil proa by Topher Dawson. I can’t remember where I saw the picture, though.
As I understand, the pivot axle is not level, such that as the foil hinges downwards it increases in pitch, giving more down force.
I copied that idea from Giles Whittaker for my models. Report on what results I’ve got is on the yahoo AYRS group and in Catalyst 45.
I assume the Proa does not have this?
It can be done. The method I first thought of was a bit complicated: introduce another transverse rotation axis. Fritz Roth has found an ingeniously simple solution: his hinges seem to consist of short strips of seat belt, and there is a bit of play in them. He can control how much by varying the gap between the foil end of the straps and the boat end. Drag will make the foil pitch down in the direction of movement.
You might not even need that. After all, the longitudinal symmetry of proa hulls means they usually sail a bit bow down. I actually started worrying what that would do on a dead downwind course.
In harbour the foil would lifted, significantly reducing the beam.
I favour very wide separation between the hulls, for maximal rotational inertia, and keeping the foil in between. Fritz correctly points out that this limits how much benefit I could get from the foil, and considers it inefficient. I like that the foil should remain effective over a wider range of heeling angles, because its own angle to the water changes less. And the wide beam would allow setting a staysail further to weather. If the location of the foil is about the same, the wider boat can use the staysail more effectively to balance the foil’s drag.
Regards
Robert
I think I once saw a picture of a canoe converted into a vector foil proa by Topher Dawson. I can’t remember where I saw the picture, though.
I remember seeing that. It was on the proa_file list and the photos may be in the files section there somewhere, or it may have been a link. Perhaps search the proa_file forum.
I modified one of my models to add a vector fin. I modified the idea by attaching the vector fin to a chord that is in tension between the stems of the ama. The vector fin hinges on the chord but can slide on the chord fore and aft to change the CLR (i.e. for steering). I never got around to finishing and testing the model, so I don’t know how well it works.
hello .....
the videos or not speeded up > and the breakers are not increased !
and the play in the vf hinge is vital !
or it will flip at the first big blow > since the stern will depress at high speeds
the bow coming up like on a power boat >
making the angle of attack > of the vf > negativ > so it will come out !
all in all .... I can not believe ..... how well this hinged vector fin proa principal works
thanks to robert biegler > or I would have been just to complacent ..... to develop it all these years !
hoping to bring all those domestic problems .... I am having with my surroundings to an end >
to be testing the .... man sized hvfp ! ...... soon .....
http://www.proadesign.com http://blog.proadesign.com
I know many of you are as well interested in ecology
a new thinking ..... of how to do things >
so here you can find same new ideas .....
there is as well a forum there to be checked out .....
http://communication.galacticdesign.org
regards fritz
Dear Fritz,
good to see you posting and thanks for your reply.
I did not really think the video was speeded up, more a comment on how fast the model was going!
I have not been following the Vector fin development. Robert mentions the clever hinge arrangement, simple but ingenious. From your comment I guess it will have to be held down on each tack to stop it flipping up.
My thought to add is that a line from the vector fin could operate a sheet release mechanism. (I have thought of using a small float for this purpose).
cheers
Mark.
PS have crossed the Gibraltar Straights in the Hydrofoil many years back - some testing waters!
I modified one of my models to add a vector fin. I modified the idea by attaching the vector fin to a chord that is in tension between the stems of the ama. The vector fin hinges on the chord but can slide on the chord fore and aft to change the CLR (i.e. for steering). I never got around to finishing and testing the model, so I don’t know how well it works.
If it is a single line, I would expect that the foil veers off to windward, that it has a lot more freedom to pitch (might there be instabilities?) and that you would have a high compression load between stem and stern. But if you had two lines, each between a stem and the middle, then the foil’s beams would always slide to close to where the lines attach to a fixed point, limiting movement.
From your comment I guess it will have to be held down on each tack to stop it flipping up.
What do you mean by flipping up?
My thought to add is that a line from the vector fin could operate a sheet release mechanism. (I have thought of using a small float for this purpose).
Rob Denney had the float idea as well. The details are probably somewhere in the Yahoo harryproa group files.
Regards
Robert Biegler
I tend to agree with your points Robert, but having a central connection pint for the chord will almost halve the range of movement.
Below are some photos of the model with sliding vector fin. Note that in this implementation the lines that control the fore and aft location of the foil form a continuous loop with the rig shunt line so that as the rig moves forward the foil moves aft.
... and here’s a detail shot of the foil connection.
Dear Fritz,
good to see you posting and thanks for your reply.I did not really think the video was speeded up, more a comment on how fast the model was going!
...... amaising .... isnt it ??? .... and how it will spin in circles and find its way all with out any external control !
or laying flat on the water > wind being on the wrong side > turning around !!!
I have not been following the Vector fin development. Robert mentions the clever hinge arrangement, simple but ingenious...... the material being from the side wall of a car tire > having nylon webing in it !
From your comment I guess it will have to be held down on each tack to stop it flipping up.
...... the water drag on the fin from going either way > does the neccessary adjusting for the fin !
My thought to add is that a line from the vector fin could operate a sheet release mechanism. (I have thought of using a small float for this purpose)....... as much as I can reckon now > we will need such > just for the safety of the rig !
so maybe we need to have the boat shoot up ..... some .... if not attended ?
I just want to test it now ...... to find out all the details .....
below is a footage of mike stolles testing > but you need to be a member to get in !
http://de.groups.yahoo.com/group/proadesignde/files/mike stolle test 4/
cheers
Mark.PS have crossed the Gibraltar Straights in the Hydrofoil many years back - some testing waters!
......... I know > done all my serious testing there !
between 1995 .... 1998
The vector-foil configuration has a lot of potential, Sailrocket 2 pretty much proved that. The question is if some of that speed potential can be realized in a way that’s suitable for cruising. 😊
Please correct me if I’m wrong, or missing something, but as I understand it the primary issue with bruce (or vector) foils is making sure that the foil stays in the water at all times, otherwise you have a dynamically unstable and potentially very dangerous system. The way I see it, there are two solutions to that problem:
1. Hinged foil on a windward ama, rig mounted on the vaka as normal
2. Sailrocket approach: fixed foil on the vaka with the rig mounted on the now leeward ama. Using a tilted (lifting) rig to ensure the ama is not forced down into the water, is also necessary to avoid making an atlantic proa out of the whole thing
Does having the ama to leeward with a lifting rig have any significant disadvantages over the ‘normal’ pacific proa configuration (which the hinged foil maintains)? What are the advantages of a hinged foil, as opposed to the sailrocket’s approach? In the Gardagast thread Robert said:
Sailrocket has no problem with that fixed foil working only over a limited range of heel angles because her leeward lifting rig makes her heel to windward anyway.
Why would heeling of the boat be an issue for the foil on Sailrocket? As long as the foil stays in the water and the angle of attack stays more or less the same, where’s the problem with a bit of heeling?
Marco
PS - Welcome to the forums Fritz Roth! It’s great to have you here in this topic in particular.
Does having the ama to leeward with a lifting rig have any significant disadvantages over the ‘normal’ pacific proa configuration (which the hinged foil maintains)?
A boat with a lifting rig to lee needs to be very wide. The balance between the rig’s forces on the lee side and the drag to windward only works for one fixed course. You must think of the alignment between forces from movement through air and water in three dimensions, though for course stability it is often enough to draw the forces as seen from above, not from the side. With the rig far to lee, you get the same trait you already see in Pacific proas, that the drag to windward gives you weather helm. The only hull you should fly is the lee hull. If you have a rig inclined to weather and the balance of forces is such that the boat heels to lee, the rig becomes more upright and the effective angle of attack increases. The speed sailing crowd found out decades ago that an inclined rig should either have no heel or heel to weather, like Sailrocket does. But if you heel to weather, the couple between leeward rig and windward hull never disappears or even decreases, as it may in a convential Pacific proa to the degree that it lifts the ama.
Therefore you need a variable geometry. If you want to sail further from the wind, your rig must swing forward. Sailrocket actually has that, though I don’t remember whether it can be adjusted while sailing. But once you commit to adjusting the geometry of your boat while sailing, you move large masses relative to each other, so you need adequate power. In theory, a boat can be designed to be self-aligning, at least in flat water (for details, see my article in Catalyst 23 at http://www.ayrs.org/catalyst.htm). I have no idea whether that would still work in a seaway. I did not bother building models to test that because the thought of the integrity of the boat depending on very highly loaded moving parts worried me. A hinged vector foil proa at least remains an intact boat if the hinge should ever fail. Of course, you might then capsize, but at least proas are the multihulls most suited to being rightable. If instead your boat falls apart because one of the hinges of your variable geometry setup failed, I think that would be a bigger problem. That’s why I have gone off the idea. Probably throwing money and diligent maintenance at the problem could solve it, but I enjoy sailing more than maintenance, and want to keep the ratio of hours as much in favour of sailing as possible.
Longitudinal stability is the other reason why you would need variable geometry with a lifting rig to lee. Now you really need to think about force vectors in three dimensions. The force from the sail should be roughly aligned with whatever gives you stability. Sailrocket 1 had a wee problem with that, in that the force from the sail was too far forward of the weight, and when it lifted too far, the wing profile of her crossbeam took over. The resulting backflip is on youtube. And that was only a small misalignment of forces, they just happened to be large forces, then a positive feedback loop. Sailrocket 2 is designed to lift her stern a little, then the crossbeam and the horizontal part of her wing lose a little lift, stabilising her. If you don’t think about that sort of thing, and you arrange for effectively unlimited transverse stability while neglecting longitudinal, you’ll crash in similarly spectacular fashion.
A boat which did have variable geometry was the French proa Rosieres. However, she was most definitely not designed to be self-aligning. To avoid the problems of having to keep the two hulls parallel, Rosieres ama could rotate 360 degrees and had a fin at the stern. That meant it only ever had drag, and no lateral resistance. That meant that the variable geometry could never contribute to aligning the horizontal force components, but was only intended to adjust longitudinal trim. And it meant that the most stable angle for the ama was right behind the boat. Any heeling would only increase that tendency. At the start of a Route du Rhum transatlantic race in the mid 80s (I think 1986), the skipper moved the ama further back, the forward trim line slipped off the winch, and the boat folded up. The self-aligning design I favour, with most or all the lateral resistance to windward, would at least not do that, but would have all the other issues outlined above.
A vector foil proa, especially one with a hinged foil, which needs to be a bit wider, is also a boat which would have a problem with getting sail and foil forces to align for stable yaw. You could go for variable geometry. You could move the foil, as Malcolm has shown. Fritz’ solution is simpler: the windward staysail brings the centre of effort to windward, reducing any torque the rig exerts around the vertical axis. During our last intensive discussion of foil stabilisation, about 12 years ago, I didn’t notice how important that was to the whole design if you want to keep things simple and especially if you want to reduce how much highly loaded structures have to move. Mentally rotate Malcolm’s model so that you look at it from above. With the foil all the way aft, what course to the apparent wind would roughly align the forces so that foil and sail force vectors are in line? About 45 degrees apparent wind angle?
Why would heeling of the boat be an issue for the foil on Sailrocket? As long as the foil stays in the water and the angle of attack stays more or less the same, where’s the problem with a bit of heeling?
Sorry, I expressed myself badly. It’s not a problem, I expect it to be an advantage. The more the hulls clear the water, the less likely it is that a wave could bounce the whole boat out of the water faster than the foil can compensate.
Regards
Robert Biegler
hello ..... mal and robert !
if you want to have a sliding hinge .....
you can use a semi circular slide track >
the semi circle going to wind ward and down ward !
those ....
the drag on the fin will slide it towards its end position
where as the end angle of the semi circle > determines the aoa of the fin
horizontally and vertically .....
the vertical component being important >
because then and only then ....
can you have the problem of the vector fin coming out !
so .... the aoa of the lower part of the vf being the difference between sailing and the end of ......
and ..... you can have 2 tracks> one on each attachement of the Y >
then the tracks being shorter in lenght > can be straight !
but toward the center > to wind ward > and this difference will determain > the aoa !
and since the lateral area is so far to wind ward .....
stearing is done best on a vfp > with having a small jib at the then bow
always sheeted tightly >
and the setting of the main determains the curse sailed !
or any other multible rig .....
this is how I sailed the vfp for years >
the rudders are mainly for small adjustments of the curse ......
let me know if any thing is not clear to you .....
fritz
First off, thank you very much for taking the time to write your long and informative post! While writing this response I realized just how much of an issue you’d have with weather helm with the rig mounted on a leeward ama. Even worse is that the moment trying to turn the boat to weather would vary dramatically depending on whether you’re sailing close-hauled or on a broad reach. That pretty much kills the sailrocket configuration for sailing that involves widely varying courses relative to the wind.
The hinged vector foil also has some issues with weather helm, but at least the moment turning the boat to weather is only caused by the drag of the foil, which is rather small compared to the drag of the main hull, or compared to the moment caused by mounting the entire rig on a leeward ama.
Personally I don’t think you’d have issues with longitudinal stability on a cruising proa. My line of thinking is something like a Jzerro-style proa with a bruce foil and a Gibbons-Dierking wingsail rig. The greater weight of the boat, and proportionally smaller rig (in terms of lift/weight) should ensure you don’t become airborne.
A vector foil proa, especially one with a hinged foil, which needs to be a bit wider, is also a boat which would have a problem with getting sail and foil forces to align for stable yaw. You could go for variable geometry. You could move the foil, as Malcolm has shown. Fritz’ solution is simpler: the windward staysail brings the centre of effort to windward, reducing any torque the rig exerts around the vertical axis.
At first I was thinking that adding a windward staysail completely defeats the point of the whole vector foil arrangement in the first place, but then I realized (again) that the drag of the foil is a much smaller force that the drag of the main hull, or the force from the primary rig. You really have to keep the relative magnitudes of the forces in mind when thinking about all this. Either way, it means the windward staysail can be comparatively small, just enough to counter the weather helm caused by the drag of the foil, and not more, leaving the vast majority of sail area on the primary hull, and at the correct location where the action of the bruce foil is concerned.
Weather helm aside for a moment though, what ensures that the forces between the foil and the rig stay balanced when sailing different courses? When on a reach the foil would have to be much smaller (or have its lift reduced greatly by some other means) than when close-hauled, right? Otherwise the foil would be pulling the entire boat to windward, because the leeward component of the sail’s lift is much smaller on a reach than when close hauled. What can you do about that? Retracting the foil, daggerboard style, seems a bit problematic, and on a hinged design where the foil needs to be curved, retracting the foil partially seems impossible to me. How can you solve that issue? Would you have to use multiple foils so you can retract some of them to vary the amount of force?
Marco
Otherwise the foil would be pulling the entire boat to windward, because the leeward component of the sail’s lift is much smaller on a reach than when close hauled. What can you do about that? Retracting the foil, daggerboard style, seems a bit problematic, and on a hinged design where the foil needs to be curved, retracting the foil partially seems impossible to me. How can you solve that issue? Would you have to use multiple foils so you can retract some of them to vary the amount of force?
I just realized that’s a non-issue. The lateral resistance of the boat should be high enough that the whole thing is insignificant.
That leaves the issue you were talking about; that the foil needs to be located on a line perpendicular to the sail to avoid causing very large amounts of weather helm… I have to say that I’m not too fond of the idea of having a highly loaded hydrofoil attached to a rail so it can slide around, as is the case in Mal’s model. Sounds like a recipe for trouble, but at the moment I can’t think of anything better either… :/
That leaves the issue you were talking about; that the foil needs to be located on a line perpendicular to the sail to avoid causing very large amounts of weather helm… I have to say that I’m not too fond of the idea of having a highly loaded hydrofoil attached to a rail so it can slide around, as is the case in Mal’s model. Sounds like a recipe for trouble, but at the moment I can’t think of anything better either… :/
As food for thought, in case you haven’t come across it yet, here is the link to my earlier work on this type of thing: