Nrg85

gyro autopilot compas heading

Recommended Posts

Hi all.

Autopilot with gyro.

Steering sailboat under assymetric

Steering on apparent wind, autopilot is using gyro information to keep the boat going and not to round up, autopilot can change course, bear away or head up to keep boat in control.

What if the same pilot is steering on compas heading? Under assymetric. Does he still uses gyro information to keep boat in control? Does he change course when it have to (bear away and head up) to keep control and than to go back to desired heading course?

 

Share this post


Link to post
Share on other sites

That depends on what brand of autopilot you have. NKE for example does not engage the Gyro unless you have a gain > 3. 

Share this post


Link to post
Share on other sites

I understood the gyro "compass" was not used for heading as much as sensing the rate of turn. If it controls the rate of turn then the heading is stabilized. It is more sensitive. Like steering "by the seat of your pants" vs. reacting to the compass.

Excels at preventing round-ups. However adjusting the various gains in an autopilot system is a black art.

Share this post


Link to post
Share on other sites

I think daddle has it right. These days there is a lot of fancy integration of sensors. The details involve fancy sensors (eg. MEMS), fancy math (eg. quaternions) and fancy control schemes (eg. PID). At a higher level, the magnetic sensor keeps track of the heading, the gyro keeps track of the rate of change in the heading and the pilot looks at the errors over time and tries to minimize them.

Share this post


Link to post
Share on other sites

Under the hood there is something called a PID loop that controls the pilot's response.  This uses various orders of derivatives the value being controlled (heading).

It would use heading and also rate of heading change as parameters.  A gyro allows for much better rate of heading change data than trying to determine that from successive compass headings.

Share this post


Link to post
Share on other sites
On ‎8‎/‎17‎/‎2018 at 6:58 PM, daddle said:

I understood the gyro "compass" was not used for heading as much as sensing the rate of turn. If it controls the rate of turn then the heading is stabilized. It is more sensitive. Like steering "by the seat of your pants" vs. reacting to the compass.

Excels at preventing round-ups. However adjusting the various gains in an autopilot system is a black art.

Ok, with more sensitive rate of turn the steering is better.

Does that mean that the autopilot will change the course to keep the boat relative flat (and in control) even if that means that he won't steer to the desired compas course but after he stabilize the boat autopilot will head back up to the desired compas course?

Or will that course changes be minimal because autopilot know that the sailboat is heeled (gyro info) so it doesn't need to change course (like it would if it uses only compass headings and he thinks that sailboat isn't going in right course when it heels)?

So he don't need wind information to sail on desired compas heading but to be able to use gyro information?

We are talking downwind sailing on waves.

 

Share this post


Link to post
Share on other sites

Found this article:

 

But another way is to use a rategyro added to this flux gate.
In short why; A flux gate compass is affected by acceleration, with the movements of the sea, depending on their strength, it's measurement is then false for a short while, and with the inertia comes slowly back to the real value. That's why a standard pilot tend to steer in curves when the conditions are becoming harder. The added rategyro inside the computer detects immediately the accelerations in the horizontal plan, and a gyro is then able to correct the compass value, what gives a good reference to the pilot to steer a more straight course. And an added rategyro creates smaller rudder changes. Every steering reaction creates drag, how bigger the change how more drag. So the rategyro should make your speed higher. And to sail in curves makes your route longer.

 

Essentialy it is what Daddle said.

So my question was does gyro need wind information. According to all this it is not necessary.

 

Share this post


Link to post
Share on other sites
4 hours ago, Nrg85 said:

Found this article:

 

But another way is to use a rategyro added to this flux gate.
In short why; A flux gate compass is affected by acceleration, with the movements of the sea, depending on their strength, it's measurement is then false for a short while, and with the inertia comes slowly back to the real value. That's why a standard pilot tend to steer in curves when the conditions are becoming harder. The added rategyro inside the computer detects immediately the accelerations in the horizontal plan, and a gyro is then able to correct the compass value, what gives a good reference to the pilot to steer a more straight course. And an added rategyro creates smaller rudder changes. Every steering reaction creates drag, how bigger the change how more drag. So the rategyro should make your speed higher. And to sail in curves makes your route longer.

 

Essentialy it is what Daddle said.

So my question was does gyro need wind information. According to all this it is not necessary.

 

I am not familiar with the more advanced autopilot tech like might be used on grand prix round the world yachts...

But the basic gyro does not use wind. It is just a much more reliable indicator of heading changes than a fluxgate compass. But the gyro system has small errors in sensing and computation that cause it to slowly drift from true heading. So in a few minutes (??) the true heading would wander. Nothing is perfect. So the computer has a formula to use the rate gyro for actual steering from moment to moment. It uses the fluxgate compass to make longer term (slower) adjustments to the steering to hold the commanded heading..

Wind is another input to the formula. As I understand it...wind is not used directly for steering. That would be as ridiculous as trying to steer by looking only at the wind instrument (however some people try). Wind is used to adjust the desired heading. It is slowly adjusting desired heading as you might do by twiddling endlessly with the A/P heading knob. Same with cross-track error.

An advanced A/P might be able to sense sea motion with 3d information from the rate gyro. It could detect the stern rising on a wave, or very small changes in actual speed, for example.

If you looked inside a fluxgate compass you would see why. The sensor just hangs inside on gimbals. It must flop around wildly in rough conditions.

Share this post


Link to post
Share on other sites
5 minutes ago, daddle said:

If you looked inside a fluxgate compass you would see why. The sensor just hangs inside on gimbals. It must flop around wildly in rough conditions.

Yeah, you can actually hear them rattle if you manipulate one before installation. I opened up an old Autohelm unit and was surprised to find there was no damping oil or the like. 

Share this post


Link to post
Share on other sites

On a newer autopilot it's entirely possible that it will integrate all data when in wind mode.  We have a simrad pilot and as you add data IE speed Gyro etc it gives more options, set drift etc.  On ours you can select multiple pilot modes, in the wind mode it's steering off of wind angle at a entered deviation.  As said above most pilots use a built in logic block similar to a PID, a proportional process control that looks at a set-point value "desired heading" and the relationship between "actual heading"  in time and offset amount correcting via optimal tuned settings.  When you commission a pilot doing S turns or loops etc the pilot is tuning these set points to optimize your pilot to your hulls response.  On most controllers you can go in and adjust these set points up or down to fine tune things to your liking.  you may even be able to have multiple profiles IE "downwind", "Upwind" or "Motoring"  Be warned tuning a PID is very much diving head first down the rabbit hole for the OCD afflicted.

Share this post


Link to post
Share on other sites

The pilot could use the rate gyro combined with the fluxgate compass to improve the accuracy of the compress heading reading, vs just the compass alone.  The technique is called a Kalman filter.  You can go another step, use the rate gyro to predict how much the compass heading should change, use the corrected compass heading to predict how position should change, and use that to correct GPS positions.  At each step one is basically integrating the variable of the previous step, using a filter to combine short term accuracy of the rate with the longer term accuracy of the instrument that measures the integral of the rate.

I don't believe pilots use wind data to control the pilot directly.  The wind is just way too noisy in the short term and the tiller would be bouncing all of the place trying to match the flutter of the masthead windvane.  One needs to average that wind direction over a period of time to reduce the noise.  But that would be too slow for a pilot and it would take way too long to react to real course changes.  So what they do is steer a compass course that's X degrees from the apparent wind's compass course.  And periodically adjust the compass course desired to stay X degrees from the apparent.

Maybe the grand prix yachts with accelerometers in the masthead wind unit can do more to steer to the wind.

Share this post


Link to post
Share on other sites
On 8/17/2018 at 9:03 AM, Nrg85 said:

Hi all.

Autopilot with gyro.

Steering sailboat under assymetric

Steering on apparent wind, autopilot is using gyro information to keep the boat going and not to round up, autopilot can change course, bear away or head up to keep boat in control.

What if the same pilot is steering on compas heading? Under assymetric. Does he still uses gyro information to keep boat in control? Does he change course when it have to (bear away and head up) to keep control and than to go back to desired heading course?

 

Disputes all the words above the short answer is no, in compass mode all the pilot will look at is heading, with a gyro stabilized compass that heading input will be orders of magnitude better than a standard flux gate but wind shifts will not be considered. The other thing you should be looking for if this matters to you is a pilot that steers to True Wind angle not Apparent, far more stable.

Share this post


Link to post
Share on other sites

I thought the whole point of steering to the wind is so you don't need to change the set of the sails. How do you do that with True Wind angle in anything but a strong, steady breeze and relatively calm waters? I would think that if the wind is flukey and/or the waves are high/abeam that the delta between true and apparent would be too unstable.

Share this post


Link to post
Share on other sites

When running deep, especially with larger waves, AWA slews around a lot as the boat accelerates on wave faces - because the AWA goes forward, steering to AWA often results in the pilot driving deeper and into gybes and the resulting mess. For these reasons, we steer to TWA when sailing off the wind.

Upwind, the subtle changes in AWA that result from sea state and/or small changes in TWS, combined with a good pilot, will improve VMG. These apparent lifts and headers aren't seen in the TWD.

Upwind - AWA

Downwind - TWA

Reaching - depends on sea state, hull form and pilot

 

Share this post


Link to post
Share on other sites
33 minutes ago, IStream said:

I thought the whole point of steering to the wind is so you don't need to change the set of the sails. How do you do that with True Wind angle in anything but a strong, steady breeze and relatively calm waters? I would think that if the wind is flukey and/or the waves are high/abeam that the delta between true and apparent would be too unstable.

Exactly the opposite. Apparent angle is affected by many things not the least of which is acceleration. If you start surfing down a wave the apparent will be pulled forward and a pilot steering to that angle will react to a “shift” that isn’t real by bearing off, possibly leading to an unwanted gybe. True values take this into account and result is far more stable and safe control of the boat in changing conditions. Of course this assumes a system that is performing calculations rapidly enough to matter. It’s true that many don’t but the good ones do and it really does matter. 

Share this post


Link to post
Share on other sites

Except TWA is computed from AWA. I find that the small errors in SPEED, HEADING and AWA sensing gives big errors in TWA. It's trigonometry. Besides, all good drivers will steer down when the wind goes forward on a surf...as that is presumably the direction one wants to go: towards the sunshine and Tiki Bars.

Rolling and pitching screw up AWA and thus TWA. Surfing and passing waves momentarily mess with SPEED. A good pounding will send HEADING off. All those errors mess with TWA so any short-term steering to that seems perilous.

However, whatever works in the given situation is the rule. Whatever gets the job done.  Nothing inherently wrong with using TWA as a steering guide.

Share this post


Link to post
Share on other sites

Sounds like a big issue is just having the AP control parameters set for high frequency response. If the time constant of the AP is longer than the periodicity of the waves, it oughta just plow on through wave-induced perturbations of AWA and, by extension TWA.

Share this post


Link to post
Share on other sites

Daddle,

All good drivers steer down and into gybes? Really? Is that the definition of good driver?

Trust me on this, it's always better to keep one's mouth shut and allow others to think one is an idiot than to open one's mouth and remove all doubt.

Stream,

If the "time constant" of the auto pilot is longer than the 6-10 seconds of typical mid-ocean swells, then you might just as well tie the tiller down and not use a pilot at all. You try driving upwind and down wind and not adjusting tiller position at a rate faster than the periodicity of the wave train and see where the boat winds up.

  • Downvote 1

Share this post


Link to post
Share on other sites
12 minutes ago, Moonduster said:

All good drivers steer down and into gybes? Really? Is that the definition of good driver?

Trust me on this, it's always better to keep one's mouth shut and allow others to think one is an idiot than to open one's mouth and remove all doubt.

Did I say steer into a gybe? Really? That would be silly indeed. I wrote "steer down when the wind goes forward." That's patently obvious. Steering up cannot be good. Steering straight ahead is slow unless one also has an automatic spin sheet trimmer.

IStream may have meant to keep a long time constant on the wind direction term. That's what I do.

Share this post


Link to post
Share on other sites

That is what I meant but I've stopped trying to explain myself to Moon.

Share this post


Link to post
Share on other sites
1 hour ago, Moonduster said:

The fact remains you're both wrong. We use AWA upwind and TWA down wind on any boat with a pilot equipped to do so.

 

But what mode do you use when reaching? 

Share this post


Link to post
Share on other sites

That depends a lot on the sea state and the hull form of the boat and how deep you're reaching. It generally is pretty simple to tell which works better and with any boat one gets a handle on when the cross over works best.

Share this post


Link to post
Share on other sites
On 8/24/2018 at 7:24 AM, Moonduster said:

The fact remains you're both wrong. We use AWA upwind and TWA down wind on any boat with a pilot equipped to do so.

 

Despite the fact that Moonduster has the kind of personality that means he has to pay for sex, he is correct about pilots. TWA for VMG is running, AWA for upwind. Reaching depends, but often times is heading. 

Share this post


Link to post
Share on other sites

Would autopilot with gyro but without wind information do good job steering down the waves?

Share this post


Link to post
Share on other sites
2 hours ago, Nrg85 said:

Would autopilot with gyro but without wind information do good job steering down the waves?

Yes. In cruiser mode where winning is not important. Like said above, gyro makes the response to heading changes much quicker and certain. 

Share this post


Link to post
Share on other sites

I rarely post, so I'm preparing for the ritual newbie insults. 

On high performance boats, if the autopilot steers to a constant TWA offwind, it also needs to monitor boatspeed.  The reason is that on high performance boats, you can end up with the boat on the desired TWA, but far too slow with the AWA far too deep.  That can be a stable condition from which a pilot that only uses TWA will never recover because the boat will never speed up when sailing at such a deep AWA.   Of course good human drivers keep an eye on the target boatspeed and in that low and slow situation (even though at target TWA) would immediately head up, speed up, and then as the boat accelerates and the AWA goes forward, they come down again to the (same) target TWA, but at near the target boatspeed.

When sailing offwind in wind speed that is light and puffy, especially in flat water, having the pilot steer to a constant AWA can sometimes work pretty well, because the sail trim stays correct as the pilot deals with the puffs and lulls and the boat speeds up and slows down.  Using the constant AWA mode in light and puffy air, the boat heads up at the beginning of a puff when the AWA goes aft, and heads off as the boat accelerates in the puff as the AWA goes forward..  The target AWA in these situations would be well ahead of the beam.  

When sailing upwind in high performance boats, Moon (as usual) is  right that the pilot needs to steer by AWA, but on high performance boats the autopilot also needs to monitor boatspeed.  The reason is that if the water is really flat, a high performance boat will start to sail too fast, which causes the AWA to go forward, and the boat to bear off, until it ends up reaching around at a speed far above the upwind target BS, at far too low of a TWA to make much progress upwind.  Human drivers of course avoid this by keeping an eye on the target UW boatspeed and not exceeding it by pinching up as necessary. 

The wrinkles above are only problems for relatively fast boats, i.e. SC70 or faster.

  • Like 1

Share this post


Link to post
Share on other sites

Stan, that’s what I find with AWA upwind. She will sail well off the wind with the pilot none the wiser (SC50). I’ve thought it might have something to do with the necessarily poor placement of the masthead vane, too.

Wishing I had a pilot that has speed in the steering calcs.

Thanks for the detailed post “newbie.”

Share this post


Link to post
Share on other sites

I've had two generations of gyro assisted pilots (as well as unassisted), and I believe they now do more than just detect yaw. The first ones seemed to detect yaw faster than the flux gate and correct quicker. But the latest detect roll and pitch as well, as helm input begins before there is any yaw. In following seas as the stern rises and the boat begins to roll, helm input is applied just as a human helmsman learns to do. The MEMS sensors are cheap - about $1? - but the magic is in the software. 

Downwind, I've found that TWA steering depends a lot on conditions, such that a blanket statement like use TWA downwind is an overreach. In some conditions on some boats yes, in other conditions or on other boats, no. Use what works. 

Share this post


Link to post
Share on other sites

Steering to upwind by AWA is also problematic. If your speed gets way too low e.g. due to hitting a bad wave, after a tack or after a lull it takes very long to accelerate to target speed. If the boat has no speed AWA and TWA are the same. Say your target AWA is 25 deg and TWA 40 deg. At low speed the AP (or driver looking just at AWA) would steer at ~30 deg TWA resulting in very low BSP. While it should steer even lower than 40 deg TWA in order to accelerate rapidly to target speed.

Do any of the modern autopilots use heeling angle for steering? That would probably be very good upwind.

Share this post


Link to post
Share on other sites
5 hours ago, Joakim said:

Steering to upwind by AWA is also problematic. If your speed gets way too low e.g. due to hitting a bad wave, after a tack or after a lull it takes very long to accelerate to target speed. If the boat has no speed AWA and TWA are the same. Say your target AWA is 25 deg and TWA 40 deg. At low speed the AP (or driver looking just at AWA) would steer at ~30 deg TWA resulting in very low BSP. While it should steer even lower than 40 deg TWA in order to accelerate rapidly to target speed.

Do any of the modern autopilots use heeling angle for steering? That would probably be very good upwind.

Yes/no. The good ones use heel angle to account for TWA. AWA; no. The best ones use 3D hull sensors which not only account for heel/pitch angle but heel/pitch acceleration along the heel/pitch axis so it knows when a boat is surfing down a wave.

Share this post


Link to post
Share on other sites
11 minutes ago, RImike said:

Yes/no. The good ones use heel angle to account for TWA. AWA; no. The best ones use 3D hull sensors which not only account for heel/pitch angle but heel/pitch acceleration along the heel/pitch axis so it knows when a boat is surfing down a wave.

Raymarine Evo models have a 3D gyro/accelerometer/magnetometer, but as far as I know it does not steer with constant heel. It may use heel etc. to help stabilize steering, but that is another matter. These sensors are very cheap nowadays (just as cheap as a 1D magnetometer), but it's another thing to use it to its full potential. That would require quite a lot of software development and testing on water.

What I'm referring to is an AP that would take a target heel angle on a beat. So it would steer a bit higher with too much heel and a bit lower with too little heel, but still use AWA/TWA to keep the boat on a beat.

Share this post


Link to post
Share on other sites
6 hours ago, Joakim said:

Steering to upwind by AWA is also problematic. If your speed gets way too low e.g. due to hitting a bad wave, after a tack or after a lull it takes very long to accelerate to target speed. If the boat has no speed AWA and TWA are the same. Say your target AWA is 25 deg and TWA 40 deg. At low speed the AP (or driver looking just at AWA) would steer at ~30 deg TWA resulting in very low BSP. While it should steer even lower than 40 deg TWA in order to accelerate rapidly to target speed.

Do any of the modern autopilots use heeling angle for steering? That would probably be very good upwind.

I mentioned the upwind approach that I use, which is for the autopilot to use both AWA and Boatspeed, when sailing upwind.  The AWA and Boatspeed target numbers are actually looked up from a table using TWS as an index into the table. 

The AWA "target" is used as a maximum AWA, and the Boatspeed target is used as a maximum boatspeed.    One way of thinking of the algorithm is the pilot will bear off to the AWA number in order to get to the BS number, and then as the boatspeed increases, the pilot will pinch up as necessary to avoid sailing faster than the BS number.  So in the table you don't actually list the AWA number at which the boat normally sails upwind, instead you use ideal AWA to use to accelerate.  That might be 40 degrees.  In a terrible seastate the pilot will sail at that AWA as long as the BS remains slow of the BS target.

This approach solves two problems.  It solves the problem of a boat sailing too fast upwind in light air and flat water, and ending up reaching around at fat TWA's.  It also solves the problem of a boat bearing off too far in a bad seastate, attempting to get to an upwind target BS that is not achievable in that bad seastate.

 

  • Like 1

Share this post


Link to post
Share on other sites

I am reluctant to add my far less qualified comment / observation to Stan's but three tid bits:

The top end NKE pilot has a "surf" mode that does exactly as Stan describes when off wind. Taking into account 3D accelerometer data, boat speed, and wind data.   It's more aggressive in the light air, more conservative in heavy air.

 It's pretty amazing to watch it work in 20+ wind speeds and high teens boat speeds where it is steering the boat as deep as 160 TWA. It takes a pinch of courage and a pound of stupid to get comfortable with that and go catch a kip while all alone.

It also as a "Gust" mode that does what Stan describes in Upwind conditions when the puff rolls in, pinching up. 

Finally, the pilot first looks for boat speed when doing its calcs, but can fall back on GPS for speed input if BSP is not available. When Mich Des last won the Vendee, he lost his speedos very early in the race and relied on SOG as a substitute.  

Share this post


Link to post
Share on other sites
13 hours ago, stanhoney said:

This approach solves two problems.  It solves the problem of a boat sailing too fast upwind in light air and flat water, and ending up reaching around at fat TWA's.  It also solves the problem of a boat bearing off too far in a bad seastate, attempting to get to an upwind target BS that is not achievable in that bad seastate.

It also solves the problem I brought up, since the target AWA is high it will not pinch to normal AWA unless the target boat speed is already reached. To me this sounds more like target boat speed steering and AWA is only used to limit steering too low when target boat speed can't be reached for some reason at normal AWA range.

Why wouldn't the AP steer the same way downwind? Target boat speed and minimum AWA or TWA would work quite well I would guess.

Which AP brands and models have these features?

Share this post


Link to post
Share on other sites
10 minutes ago, Joakim said:

It also solves the problem I brought up, since the target AWA is high it will not pinch to normal AWA unless the target boat speed is already reached. To me this sounds more like target boat speed steering and AWA is only used to limit steering too low when target boat speed can't be reached for some reason at normal AWA range.

Why wouldn't the AP steer the same way downwind? Target boat speed and minimum AWA or TWA would work quite well I would guess.

Which AP brands and models have these features?

B&G H5000 Hercules and above or NKE with the true wind option..

Share this post


Link to post
Share on other sites

For the full package of features you really need the Vendee version of the NKE or B&G pilots. For NKE that would be their HR Pilot with the TWA option as well as the Gust and Surf options. 

Then a fair amount of calibration and practice with how your boat performs with the pilot under various settings. 

The price is a bit eye watering, but it is worth every penny. 

Share this post


Link to post
Share on other sites
16 hours ago, Rail Meat said:

For the full package of features you really need the Vendee version of the NKE or B&G pilots. For NKE that would be their HR Pilot with the TWA option as well as the Gust and Surf options. 

Then a fair amount of calibration and practice with how your boat performs with the pilot under various settings. 

The price is a bit eye watering, but it is worth every penny. 

Hi Rail Meat, What is the difference between the off the shelf H5000 ACP and the Vendee version? Is there a special software version you need to obtain from B&G at an extra cost?

Share this post


Link to post
Share on other sites
20 hours ago, Chucky said:

Hi Rail Meat, What is the difference between the off the shelf H5000 ACP and the Vendee version? Is there a special software version you need to obtain from B&G at an extra cost?

So I am an NKE guy and wont be able offer much detail on B&G. For NKE it involves adding an extra accelerometer,  software and an upgraded chip set for the gyro pilot CPU, all on top of theirbtoo end HR processor CPU and best sensor package. I am guessing it's a similar set of extras for B&G. 

Share this post


Link to post
Share on other sites

Hopefully this is not considered hijacking, but I'm thinking of entering my J35 in the 2020 Pacific Cup, sailing doublehanded (have done it before fully crewed).  I'm interested in hearing from anyone with actual experience with B+G h5000 and/or NKE gyropilots as to their suitability.  We sail with asymmetrics flown off the pole, so generally can sail fairly deep and surf if the seas are there.  I get the sense that the NKE and Alpha Marine pilots would be able to do most of the driving if need be, but I'm also considering B&G, despite the fact that I've yet to hear anyone say they've actually used a B+G pilot in a boat like mine, in conditions like we see in the Pacific Cup.  So...opinions anyone?

Share this post


Link to post
Share on other sites

Control system theory will tell you that the more gain in the system the less stable it may be to perturbations. Then again a rock is stable, but not going very fast. 

Putting in multi axis sensors for yaw, pitch, roll and their derivatives, and monitoring wind & boat speed gives the pilot the equivalent of “seat of the pants” feel. It won’t give it anticipation to hear/see the unusual wave. The software to interpret the rock and roll in a puff vs surge from a wave needs a fast processor and a high output actuator. 

Your high end pilots provide the sensing and computing, you need an actuator that can keep up, and the electrical capacity to sustain it. B&G just updated their H5000 Pilot. Release notes are here 

summary is “

B&G is pleased to announce the arrival of the latest software suite for the H5000 Pilot system. The latest software package provides multiple new features, enhancements and fixes for field issues reported by users, customers and Navico’s internal SQA teams.

Following the success of the last Vendee Globe race, the H5000 Pilot Computer has been enhanced by the addition of failsafe sources and allowing the following variables to be outputted to the displays and for logging, giving the advanced user the ability to monitor and analyse individual elements of the Pilot setup.

Active Perf Mode
Gust Bear Away
TWS Bear Away
Heel Compensation
Pilot Net Course
Pilot Target Wind Angle
Pilot Weather Helm
Pilot Mean Heel

” 

key attribute is are your data sources robust and calibrated ? Note the failsafe features for loss of speed etc. 

Share this post


Link to post
Share on other sites

This is not an application that needs a high performance processor by any stretch of the imagination. It's not compute constrained in any way at all.

The Alpha Spectra was a solid 60s era implementation in the 80s, when marine autopilots were lingering in the 40s. Unfortunately, it's still a solid 60s era implementation and Raymarine, B&G and NKE have moved into the 70s.

I'm not aware of any pilot that uses 9-axis data or any that use more than rudder angle, heading, yaw rate and heel.

I think you'll find that either the B&G or NKE pilots will drive your boat well. More important than the choice between those two is your choice of actuator - no pilot can steer well off the wind in big seas with lousy rudder slew rates. Actuator choice is orthogonal to controller choice, but the actuator, its installation and integration with your steering system is critical.

 

Share this post


Link to post
Share on other sites
5 hours ago, Moonduster said:

I'm not aware of any pilot that uses 9-axis data or any that use more than rudder angle, heading, yaw rate and heel.

 

Derivatives of the output in feedback for the P-I-D loop are classic, feeding forward derivatives of the inputs is a more modern technique; "fast" is a relative term, depending on the amount of digital filtering and signal processing, any CPU built in the last 10 yrs should be more than adequate to generate a control response at > 10 Hz (compared to human reaction time > 200msec)  

What the Vendors are doing in their algorithms is  proprietary; you can presume that since higher end instruments use the "9 axis" or similar MEMS "3D Motion" sensors to clean up the masthead motion for TWS/TWA calculations, they are built in to some extent. Do the pilots make use of hull motion;  "trim angle" and derivative "Pitch"  to sense waves, and "heel" and "roll rate" as well as TWS for gusts and generate the compensation outputs before yaw ?

Good question, if they don't they should be, and the "training" that is done for commissioning at least addresses rate of yaw vs control input

Share this post


Link to post
Share on other sites

You write:

any CPU built in the last 10 years

You really have no idea what you're talking about with respect to processor performance. We broke 1gHz in March 2000, more than 18 years ago. It doesn't take a 100mHz processor to run an auto pilot control loop in a CAN-connected instrument system and commodity processors at that performance have been around for closer to 25 years.

You wrote:

If they don't, they should be

Why? The data from a 9-axis IMU is the following with the pertinent information underlined:

  • Attitude: Heading, Heel, Pitch
  • Acceleration: Heave, Sway, Surge
  • Rate: Yaw, Roll, Pitch

Whether there's information in Heel that's not also in Yaw rate is controversial and, I expect, largely dependent on hull form. But either way, most pilots do just fine with heading and yaw rate and none will benefit from most of the other 9-axes.

 

Share this post


Link to post
Share on other sites

Your grasp of semiconductor history may be accurate in general, but it's useless in specific: sure, there were 1 GHZ  clock Server CPU's 18 yrs ago, most running well over 30 Watts, not exactly a power dissipation for the processor that was going to win market share in an offshore battery system. 

Low power "mobile" CPU have lagged behind typically, getting one that would run on less than 1 Watt, with onboard NVRAM is a bit harder than getting 1 GHz. (what would I know, it's just my industry...)

A spec of 20 Mhz is adequate, finding somebody who would make a slow processor for a small market (before smart phones, not as easy.) 

As regards 9 axis, the pitch and roll are already in the TWS, TWS corrections for masthead.. 

 

Share this post


Link to post
Share on other sites

Oh, I see ... so now you're changing your tune from performance to low power, the opposite end of the spectrum. Make up your mind, will you?

And I don't believe you'll find anyone is using pitch to correct TWS, correcting for that aspect of attitude has no effect on TWS at all.

Share this post


Link to post
Share on other sites
45 minutes ago, Moonduster said:

Oh, I see ... so now you're changing your tune from performance to low power, the opposite end of the spectrum. Make up your mind, will you?

And I don't believe you'll find anyone is using pitch to correct TWS, correcting for that aspect of attitude has no effect on TWS at all.

NKE does in their high end HR Processor. More about it on how it's used can be found on page 33 of the user manual: http://nke-marine-electronics.fr/wp-content/uploads/2017/01/43_Processor_HR_um_UK_37.pdf  There even is a nice flow chart for visualizing it. 

Share this post


Link to post
Share on other sites

Long retired from video DSP work I am...I would think many low power chips with floating point could do the PID servo loop, plus sweet filtering of the many inputs, simultaneously for 10,000 boats without even breaking a sweat. So that cannot be the issue these days. We did far more at video pixel rates 20 years ago. The marine A/P computation is trivial, while selecting the coefficients for smooth sailing is very difficult.

Share this post


Link to post
Share on other sites
9 hours ago, LionessRacing said:

A spec of 20 Mhz is adequate, finding somebody who would make a slow processor for a small market (before smart phones, not as easy.)

You don't really need anything special for that purpose. Even a 8 bit processor can do all that. An AP is always limited by the rather slow drive unit. 10-100 Hz floating point processing can be done with a $2 (in small volumes) 8 bit chip (AVR, PIC etc.). E.g. I have a 8 bit AVR chip in my boat since 2012. It does all the calculations for instruments, calculates target speeds, start line functions, displays all the data on a graphical display and writes all the instrument data on a SD card etc. At the same time it is a MPPT charge controller for the solar panel and a battery monitor for two battery banks. All that running at 4 MHz, while it could do 32 MHz, and consuming about 10 mA. Similar processors have been available for a long time. I started using AVR in 2001 and the processing speed was up to the task already then.

When did Silva release Nexus series? Early 90's? It uses a 8 bit processor to do all the instrument calculations in the server. Processors have come a long way since then.

If more power is needed (I really don't think it is!), 32 bit ARM has been available for a long time as well. I did a similar system to my previous boat using a 32 bit ARM running Linux. It was way overpowered for the task, but still took only about 200 mA at 5 V (less than 100 mA at 12 V). That was in 2007. Modern ARM could do the same at a few mA.

 

Share this post


Link to post
Share on other sites

RImike,

Again, I don't believe anyone is using pitch to correct TWS. NKE uses accelerations to compensate for mast motion, but the boat's pitch (bow up/down) has no affect on measured AWS, AWA, speed or heading, which are the components of TWS.

 

Share this post


Link to post
Share on other sites
20 minutes ago, Moonduster said:

RImike,

Again, I don't believe anyone is using pitch to correct TWS. NKE uses accelerations to compensate for mast motion, but the boat's pitch (bow up/down) has no affect on measured AWS, AWA, speed or heading, which are the components of TWS.

 

Considering that as a bow goes up and down (Mast pitches fore and aft) in rough sea state with low wind for example, the MHU accelerates/decelerates quite often. With a slow speed MHU, think 1 Hz this isn't an issue however with a MHU running at 25 Hz it is sending data that wouldn't correlate to a "smooth" TWS. Therefore the processor reads the pitch angle and makes a computation to correct for the acceleration/deceleration of the MHU. 

Share this post


Link to post
Share on other sites

Let's review the 9 components again:

  • Attitude: Heading, pitch, roll - measured in degrees
  • Accelerations: Heave, sway, surge - measured in meters/second2
  • Rates: yaw, pitch, roll - measured in degrees/second

Pitch is not an acceleration, it's an angle. And the accelerations aren't much use here either. I believe you're referring to rate data being used to extrapolate MHU velocity based on mast height. Again, my comment was specifically about pitch in response to what someone else posted.

 

Share this post


Link to post
Share on other sites
11 minutes ago, Moonduster said:

Let's review the 9 components again:

  • Attitude: Heading, pitch, roll - measured in degrees
  • Accelerations: Heave, sway, surge - measured in meters/second2
  • Rates: yaw, pitch, roll - measured in degrees/second

Pitch is not an acceleration, it's an angle. And the accelerations aren't much use here either. I believe you're referring to rate data being used to extrapolate MHU velocity based on mast height. Again, my comment was specifically about pitch in response to what someone else posted.

 

The MHU height is a know constant value to the processor, but while it's the MHU velocity, it's an input compared against the pitch angle for a corrected TWS which is what you said you don't believe anyone is doing, NKE is. 

Share this post


Link to post
Share on other sites

I understand MHU height is a known constant and that by applying the rates, one can determine mast head velocity which are meaningful corrections to AWS and AWA. However, pitch has nothing to add - to say that it does would be to say that one should apply a correction when changing mast rake, which no one ever does.

Now, NKE might be tossing all 9 elements into a Kalman filter to resolve AWS and AWA, but the output of that filter would not change if they sent constant pitch into it.

 

Share this post


Link to post
Share on other sites

Acceleration is as acceleration does. When I design a system, my rule of thumb is that if you are managing a control surface's position, velocity, and acceleration, it's nice to be able to measure the vehicle's position, velocity, and acceleration as inputs, even in the axes you aren't controlling directly, since there's often some coupling.

Share this post


Link to post
Share on other sites
Quote

 

Oh, I see ... so now you're changing your tune from performance to low power, the opposite end of the spectrum. Make up your mind, will you?

And I don't believe you'll find anyone is using pitch to correct TWS, correcting for that aspect of attitude has no effect on TWS at all.

 

Dude, you're the person who picked "1GHz"  as significant. "Performance" in digital Semiconductors has always been Speed * Power product, the ECL logic of the 60's was really fast, and eventually high speed required fluid cooling in the IBM mainframes. Getting it to run in your pocket, or on an offshore power budget required a few jumps down the ITRS

 I simply said any "CPU built in the last 10 yrs should be more than adequate to generate a control response at > 10 Hz (compared to human reaction time > 200msec) " And that's a sensible comment;  if I have to stipulate that it's suitable for battery operation at low power consumption to you, which would seemingly be obvious in the context, I did above; as that seemed to escape you in your urge to be disagreeable. 

You continue to gloss over that fact that 3-D acceleration is used to correct the measured WA and WS to account for the mast's motion (pitching, rolling, not heel & rake, nor static boat trim) which causes the sensor at the mast head to be moved in the wind field, creating a spurious apparent wind component that would be cyclic in waves and a declining impulse due to gusts as the boat heeled to equilibrium. 

Correction for Trim & Heel are implicit the static calibration tables at various TWS & TWA that are done in the processing by the instrument's CPU before the AWA, TWA are let out onto the NMEA buss as well as heel correction of boat speed.

I don't know the proprietary algorithms, but I did read the release notes

Autopilot: Advanced Mode ...  will then allow access to the following advanced features for configuration: • Gust Response • TWS Response • Heel Compensation 

(Heel Compensation HEEL COMP The amount of applied Rudder Angle to counteract any heel induced broach) 

Share this post


Link to post
Share on other sites

No, you said:

The software to interpret the rock and roll in a puff vs surge from a wave needs a fast processor and a high output actuator.

And that's bullshit by any measure. I chose the 2000 1gHz milestone because performance changes over time but your claim was bullshit by standards nearly 20 years old.

I stand by my claim that acceleration is not used to correct wind speed - rate gyros are used. Surge, sway and heave have nearly no effect.

 

Share this post


Link to post
Share on other sites

Just out of curiosity, we've got a 42' 20,000lb cruising boat that normally chugs along at 6-7 knots - we surf a bit, but by no means high performance.  The boat came with an Autohelm/Raymarine ST6000 autopilot with a gyro and a Raymarine below decks type 1 electric linear drive.  If and when we need to replace this system as it's all pretty old electronics, what's the go-to?  

Are there more robust drive units than the Raymarine ones that we should be looking at?  The boat came with two of the drive units - we broke one, and are now on number two.  This drive seems to be unchanged in the Raymarine lineup between whenever ours were built and today.

We certainly don't need the performance of a Vendee boat, but suspect and hope that there have been some improvements in software and hardware since this equipment was built.  What we have works just fine, but isn't great at dealing with big gusts or steep waves.

Share this post


Link to post
Share on other sites

The Raymarine linear drives aren't bad, especially if the version you have doesn't use plastic gears.

They have upgraded their heading sensors over the years and now have a yaw rate gyro, I believe they call it a rate compass.

If you're happy with the pilot, it's probably just as well to stick with it.

If you're looking for different capabilities - Steer to a way point, follow a route, steer to AWA or TWA, then you need to reconsider your instrumentation system. That said, you can probably use the same actuator if you're happy with its performance and installation.

Share this post


Link to post
Share on other sites
4 hours ago, hdra said:

Are there more robust drive units than the Raymarine ones that we should be looking at?  The boat came with two of the drive units - we broke one, and are now on number two.  This drive seems to be unchanged in the Raymarine lineup between whenever ours were built and today.

I my experience...the RM underdeck drive is a solid reliable unit if kept dry. Tore my down for inspection after a ten year loop around the entire Pacific. Looked like new inside. Even the belt.

The electronics are a different matter. That they make no attempt at weatherproofing is remarkable. And the tech seems to be stuck in the 1980’s. But the biggest problem is the software which is buggy, clunky, and never updated with bug fixes. Plus, simply watching the software response to difficult steering conditions it is obvious something serious is lacking. The user interface makes it clear no designer who matters at RM has ever been on a sailboat but for 5 minutes.

Heh...so it is pretty much standard marine industry quality...I would probably replace it with the same.

Share this post


Link to post
Share on other sites
20 hours ago, hdra said:

Just out of curiosity, we've got a 42' 20,000lb cruising boat that normally chugs along at 6-7 knots - we surf a bit, but by no means high performance.  The boat came with an Autohelm/Raymarine ST6000 autopilot with a gyro and a Raymarine below decks type 1 electric linear drive.  If and when we need to replace this system as it's all pretty old electronics, what's the go-to?  

Are there more robust drive units than the Raymarine ones that we should be looking at?  The boat came with two of the drive units - we broke one, and are now on number two.  This drive seems to be unchanged in the Raymarine lineup between whenever ours were built and today.

We certainly don't need the performance of a Vendee boat, but suspect and hope that there have been some improvements in software and hardware since this equipment was built.  What we have works just fine, but isn't great at dealing with big gusts or steep waves.

I've had nearly every generation of Raymarine autopilot course computer from ST6000 through now. Each generation gets better than the last. The biggest jump was to the gyro corrected ones but there are incremental improvements beyond that. The latest (EVO) disposed of the swinging fluxgate and went to a MEMS solid state sensor.

If you want to upgrade the drive unit, take a look at the Jefa ones. They are hell-for-strong and the idle drag is insignificant, less than the Raymarine linear. The combination of SPX course computer and Jefa drive has driven my boat dead down wind for days in strong conditions, without a worry. A couple of generations ago I'd have had to keep a very close eye on on it. Just now upgrading to the EVO system, which users say is noticeably improved due to better heading and attitude info. 

Share this post


Link to post
Share on other sites

DDW, keep your SPX around until you decide if you like the EVO.  The EVO heading sensor is better but the pilot itself is not, in my experience.  Like you, I've been through several generations of Raymarine pilots and the EVO was the first major step backwards.  One example:  On the SPX series, you adjusted the responsiveness using a scale of 1-10.  On the EVO, it's based on boat type with no further adjustment.  Also, you can't tweak the hard-over time like you can on the SPX.  I suspect Raymarine had some customers who screwed their powerboats into the lake, so they dumbed it down for everyone.

Share this post


Link to post
Share on other sites

I have an Evo and can adjust all of those things.  Doing so it also described in the manual.  Do you have ancient firmware?

https://raymarine.app.box.com/s/g4nuab5t3b0gxx8paj9b

The responsiveness is now out of 3 levels instead of 10, but that's probably okay.  It's just like how Raymarine has gone from 100 steps of brightness to 10... sometimes there are just too many steps available.

Share this post


Link to post
Share on other sites

Interesting responses, thank you all.  I was hoping to find someone with actual experience with the H5000 pilot under conditions I'd see on a Pac Cup, but maybe it hasn't been around long enough to attract much of a following on the shorthanded circuit.  On the subject of AW correction, the larger seas that we had in 2016 induced noticeable swings in AWA just from the  motion of the mast when we rolled.  It's a shorter period than the speed effect (on AW) that you get when surfing down a swell, but sure confused me for awhile when I was staring at those displays in the dark.  Correction for this effect is one of the reasons I'm attracted to the B&G H5000 equipment, as the Hercules-level software is significantly cheaper than the NKE processor that accomplishes motion-correction in their line (assuming I understand the NKE equipment offerings correctly).

On the subject of actuators, I was pretty sure I'd get a B%G or LS ram, although if would be fast enough, the Simrad DD15 is really appealing due to the reduced resistance when the autopilot is off.  Someone above mentioned the Jefa electric drives, so a further question (in addition to the original about anyone having actually used an H5000 pilot downwind in seas in the 14' range) would be whether anyone knows if these electric drives would be a good choice?   Thanks!

Share this post


Link to post
Share on other sites

Alex, I tried the available adjustments but they seemed to have no effect on the responsiveness of the pilot.  I performed all the firmware upgrades.

I recently sold the boat and bought one with an up-to-date B&G system.  I'm glad to be done with Raymarine.

(Great to see you have Glenn I's old boat.  That's a good one.)

Share this post


Link to post
Share on other sites

I have an existing hydraulic ram with 12VDC Octopus motor which came with my boat. I have just upgraded the autopilot computer and compass from a Course Master unit ( only a cruising type setup) to a (yes bought used gear as on a budget) H3000 ACP2 with the H3000 Gyro compass which has all the performance level settings (similar to the new H5000 ACP). My existing instrument system is also H3000 performance processor so easy integration to the ACP2 (operating in TWA and AWA modes)

My boat is a light weight racing boat similar to a Class40 but with twin wheels.

I have raced on Class40 boats and I am impressed with the B&G H5000 ACP and hydraulic drive units in hard reaching running conditions. The H5000 ACP is easy to setup and commission. 

If I was to consider a replacement drive unit increase the speed of the rudder movement, should I consider the B&G drives or use the L&S units? Ie are the L&S drive a better performance drive compared to the B&G units (these are re-branded units anyway just like the gyro compass)

The B&G units are reasonably priced and appear to be reliable from my observations on the other race boats. The L&S claim to supply most of the VG/IMOCA boats.

Share this post


Link to post
Share on other sites

Hallelujah, someone who has actually used the 5000 series pilot downwind!  Chucky, could you elaborate just a little, in terms of the kind of winds and seas you were in when you talk about hard reaching running conditions?  Also, was the system running with the Hercules level software?  And were the wind sensors up top mounted on one of those (~31") masthead extensions, or the just on a wand that didn't elevate them to well above masthead.  Finally, do you know if the H5000 pilots are in widespread use on Class 40s?  I would assume that if they've achieved a decent share of active racers, then they're probably pretty well tested; however B&Gs marketing materials don't really make such a claim.  

For what it's worth on rams, a local service guy strongly advised me to use the L&S ram, saying they were as close to bombproof as you get on boats.  He also said their resistance when not being used was less than other hydraulic rams.  However, I see B&G brochures that indicate a re-design had reduced their resistance by 30%, and I'd find it hard to believe they aren't very dependable.  I think there may be some design differences that do favor the L&S, particularly in tight quarters - which is why I'm likely to go with it, although would love to hear that the DD15 was a good choice as well.

Also, you can contact me at karl@seastateinc.com if you wish to discuss any of this separately.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now