Auto-Flight
Another alternative to using a paddle is to use a secondary ‘sensor ama’. This would be a small ama, which might sit just to leeward of the ‘primary ama’. The akas of the sensor ama would be hinged at the vaka. Again, this would work best if combined with a tail controlled wingsail, because the small control input requirements for the wingsail mean that the sensor ama can also be quite small. The advantage of a sensor ama over a paddle is the much more linear and predictable response.
Mal.
Along similar lines, I’ve been thinking that it might be a good idea to combine Fritz Roth’s ‘hinged vector fin’ with the auto flight mechanism. The hinged vector fin can be used as the surface follower and since it is already a hinged structure it should be easy to adapt the sail control mechanism to it. Mal.
Marco and Mal; you both make very valid points, but in both instances you’re introducing new and significant sources of drag (due to lift) as well as grave danger of precipitating the very capsize you’re seeking to prevent (windward foil “unhook”), just to get the ama to do what it will do naturally, if simply encouraged and chaperoned.
The point of the exercise isn’t to come up with a novel way to stabilize a boat’s roll. There are dozens of perfectly viable methods to do that. The point of the exercise is to take the absolute smallest pile of parts, get them to do the job with the absolute least amount of added drag or endangerment to the boat, and to do so in a solidly engineered and failsafe fashion. I don’t mean to be blunt, but I just can’t put it simpler than that.
Oh, and I love your new signature, Mal!
Dave
In the case of the hinged vector fin, I’m advocating that it be used primarily as a sensor. You only need enough ‘vector fin’ effect to provide the force required to control the sail.
Mal.
Gary over on the Multihulls forum makes a valid objection; introducing an unguarded foil blade underwater in the open ocean risks having some form of flotsam hit it and break it. Here’s what I sent him;
I understand your reluctance to use a blade/foil/board out there where flotsam could break it, but you could always carry spares—at $20 a pop they wouldn’t amount to much. 😉 Any breakage of the (one) parts of the system would result in a failsafe failure mode—it lets go of the mainsheet. Fortunately, there’s also a complete backup system (the other end of the sheet) which the pilot can let go of as well.
If it suits an electronic bent, forget all the mechanical crap and epoxy a pair of bare wires an inch or so apart along the ama’s keel then hook them to a simple relay—either they’re in salt water or they’re in air. Break/no break in the circuit. Robust—it’d take a hammer and chisel to remove the “sensor.” Take the signal straight to a Raymarine tiller drive like this one: Linear Drive Installation Instructions 81175-5.EN - Raymarine and use it on the main boom instead of the tiller. Simple thing doesn’t need a brain. Wet or dry. Wax on, wax off.
Cheers,
Dave
Another alternative to using a paddle is to use a secondary ‘sensor ama’. This would be a small ama, which might sit just to leeward of the ‘primary ama’. The akas of the sensor ama would be hinged at the vaka. Again, this would work best if combined with a tail controlled wingsail, because the small control input requirements for the wingsail mean that the sensor ama can also be quite small. The advantage of a sensor ama over a paddle is the much more linear and predictable response.
Mal.
Yup. Here’s a primitive version (not mine—I swiped this one!) http://www.dcss.org/sheetrelease.jpg
Dave
On the sensor ama option, if you need more force than can be provided by the weight of the sensor ama, the sensor ama could just be used to control a servo paddle (like those old vane gear steering systems) and the servo paddle then provides the necessary force to sheet the sail.
Mal.
If it suits an electronic bent, forget all the mechanical crap and epoxy a pair of bare wires an inch or so apart along the ama’s keel then hook them to a simple relay—either they’re in salt water or they’re in air. Break/no break in the circuit. Robust—it’d take a hammer and chisel to remove the “sensor.” Take the signal straight to a Raymarine tiller drive like this one: Linear Drive Installation Instructions 81175-5.EN - Raymarine and use it on the main boom instead of the tiller. Simple thing doesn’t need a brain. Wet or dry. Wax on, wax off.
Wasn’t it you who objected to eletrical control for wingsails? 😊
In any case the above solution does not really deliver constant hull flying. You really need a fairly linear analog signal rather than a binary one. A wand attached to a potentiometer might be a better and still fairly robust sensor.
Mal.
This is *precisely* what the auto-flight is; how the auto-flight works. Only difference is the paddle acts as both sensor and servo. No other parts
On the sensor ama option, if you need more force than can be provided by the weight of the sensor ama, the sensor ama could just be used to control a servo paddle (like those old vane gear steering systems) and the servo paddle then provides the necessary force to sheet the sail.
Mal.
In any case the above solution does not really deliver constant hull flying. You really need a fairly linear analog signal rather than a binary one. A wand attached to a potentiometer might be a better and still fairly robust sensor.
Mal.
You could do it that way, and it would probably work, though it’d be far more complicated and fragile. I’d propose to put the “analog” bit back into the system using the built-in response time of the actuator. It cannot respond instantly, so the delay acts as attenuator. (note that this particular actuator has a zero-pressure “off” mode, so you still have the ability to instantly dump the whole sheet—whenever the power is turned off. AS an autopilot it has three modes—in under power, out under power, or full dump with system off. For the auto-flight, we only need two of these, in under power and full dump. Wax on, wax off. (In theory. In practice, you might need all three. No big thing, either way.)
As to electrical versus mechanical systems of course you know which I prefer. I’m making a point here; the concept is profoundly simple. Not naively simple but profoundly simple. As soon as one gets that into one’s head (took me a while!), the actual implementation can be done a hundred ways.
Dave
I’d propose to put the “analog” bit back into the system using the built-in response time of the actuator. It cannot respond instantly, so the delay acts as attenuator.
No. The delay will act as a delay. When the ama comes out of the water the actuator will start to dump sheet and will continue to dump sheet until it either reaches the limit of travel or the ama goes back in the water. When the ama is back in the water the actuator will start to sheet the sail on until it either reaches the limit of travel or the ama lifts back out of the water again. And so on in an oscillatory fashion. Not stable flight.
To get stable flight you will need a variable (height dependent) signal and a fast (powerful) actuator to respond to it. Without that you will only get an emergency sheet dumping mechanism at best.
Mal.
I’ve been thinking about a mechanical mixer for the tail controlled wingsail option. Below is an image of a schematic model of a possible solution. There are two inputs and one output. The manual tail control input is shown on the left of the image. The input from the ama height sensor is shown at the bottom right of the image. The output to the tail flap is shown on the top right of the image. The sensor input can modulate the manual input from zero to full throw. Hope that makes sense! The animated version is here: http://youtu.be/pf6M-9hJrwU
No. The delay will act as a delay.
The cool thing about the internet is that we’re allowed to disagree. 😉
You’re welcome to do it with an analog sensor, or you can use a whole row of bare wires, which can now sense the proximity of the water surface in a quasi-analog fashion, but without moving parts. Now you need some computing power though. Plus as you mention, you’ll need some pretty serious grunt in the actuator, so where are we going to get power?
To get stable flight you will need a variable (height dependent) signal and a fast (powerful) actuator to respond to it.
Something like the mechanical auto-flight gadget perhaps?
Dave
To get stable flight you will need a variable (height dependent) signal and a fast (powerful) actuator to respond to it.
Dave
I made that as a general statement that applies to both mechanical and electrical systems. I’m not sure whether that came accross.
Mal.
To get stable flight you will need a variable (height dependent) signal and a fast (powerful) actuator to respond to it.I made that as a general statement that applies to both mechanical and electrical systems. I’m not sure whether that came across. Mal.
Yes I did get it that way, Mal. I was just being snippy with you. 😉
It was a bit of an epiphany for me when I realized that a simple tapered blade could give both a height-dependent signal *and* act as its own fast and powerful actuator. Guaranteed? Not hardly! Worth a shot? Absolutely, IMO.
Dave
It was a bit of an epiphany for me when I realized that a simple tapered blade could give both a height-dependent signal *and* act as its own fast and powerful actuator. Guaranteed? Not hardly! Worth a shot? Absolutely, IMO.
I think it might need a little more. My mental model of events goes like this: ama lifts, sensor comes out of the water, loading increases, sensor rotates, more of the blade comes out of the water, sensor rotates more, pops out entirely, power off. This would not happen if the boat’s roll angle responded faster than the sensor, but the sensor has the lower moment of inertia and should respond faster. So either introduce some damping, which probably would make the sensor too slow to prevent capsize, or introduce some negative feedback instead of positive. I can think of two ways to introduce negative feedback, which could be used separately or in combination.
Instead of the rotation axis being parallel to the longitudinal axis, give it 40 to 50 degrees toe in. Then rotation increases the angle of attack. Then two sensor blades would be needed, one for each tack. Giving the sensor blade some twist might be safer than tapering, to be sure the foil doesn’t stall when it needs to sheet in again.
Move the rotation axis inboard, so that rotation of the sensor immerses the blade more. Or use the sensor ama.