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Autopilots
Time for a yearly update. I had a Bombardier Utopia - an 18'
jet-powered runabout that I added an autopilot to, but while it did work at higher speeds, it failed miserably for trolling and fishing in general. Last year I sold it and bought a center console Cobia, a 21' with a 150 hp Yamaha outboard. I added a 15 hp (smallest I could get without ordering) Suzuki outboard to use as a trolling motor. It is tied, mechanically, to the larger Yamaha and sips fuel from the same large tank. It works pretty well, and steers a straight course with no hands on the wheel. Still, I'd like to add an autopilot IF (and only if) it can operate at trolling speeds (about 1 knot or 1.5 mph). ComNav makes a few units which look like they'd work, but I'd like to hear that from someone other than the manufacturer or salesman, preferably someone who owns one. The boat is equipped with a Garmin 540 combination fishfinder/GPS chartplotter which issues NMEA sentences. -- Larry rapp at lmr dot com |
Autopilots
"Larry" wrote in message ... Time for a yearly update. I had a Bombardier Utopia - an 18' jet-powered runabout that I added an autopilot to, but while it did work at higher speeds, it failed miserably for trolling and fishing in general. Last year I sold it and bought a center console Cobia, a 21' with a 150 hp Yamaha outboard. I added a 15 hp (smallest I could get without ordering) Suzuki outboard to use as a trolling motor. It is tied, mechanically, to the larger Yamaha and sips fuel from the same large tank. It works pretty well, and steers a straight course with no hands on the wheel. Still, I'd like to add an autopilot IF (and only if) it can operate at trolling speeds (about 1 knot or 1.5 mph). ComNav makes a few units which look like they'd work, but I'd like to hear that from someone other than the manufacturer or salesman, preferably someone who owns one. The boat is equipped with a Garmin 540 combination fishfinder/GPS chartplotter which issues NMEA sentences. -- You need an autopilot where you can alter the amount of response to a given course deviation. At trolling speeds you need much more rudder angle to correct a deviation than you would at higher speed. However, if you are trolling rather than maintaining course to a destination you ought to be able to accept a greater amount of yawing about the set course anyway. |
Autopilots
Just what the world needs - another autopilot jetboat jerk who hasn't a clue
as to how to safely operate a boat blasting around the water becoming a big nuisance and even larger menace to all concerned. Take your autopilot, and overgrown Jetski for that matter, and shove it up your ass! -- Gregory Hall "Larry" wrote in message ... Time for a yearly update. I had a Bombardier Utopia - an 18' jet-powered runabout that I added an autopilot to, but while it did work at higher speeds, it failed miserably for trolling and fishing in general. Last year I sold it and bought a center console Cobia, a 21' with a 150 hp Yamaha outboard. I added a 15 hp (smallest I could get without ordering) Suzuki outboard to use as a trolling motor. It is tied, mechanically, to the larger Yamaha and sips fuel from the same large tank. It works pretty well, and steers a straight course with no hands on the wheel. Still, I'd like to add an autopilot IF (and only if) it can operate at trolling speeds (about 1 knot or 1.5 mph). ComNav makes a few units which look like they'd work, but I'd like to hear that from someone other than the manufacturer or salesman, preferably someone who owns one. The boat is equipped with a Garmin 540 combination fishfinder/GPS chartplotter which issues NMEA sentences. -- Larry rapp at lmr dot com |
Autopilots
Larry wrote in
: Still, I'd like to add an autopilot IF (and only if) it can operate at trolling speeds (about 1 knot or 1.5 mph). ComNav makes a few units which look like they'd work, but I'd like to hear that from someone other than the manufacturer or salesman, preferably someone who owns one. The boat is equipped with a Garmin 540 combination fishfinder/GPS chartplotter which issues NMEA sentences. -- If this is the only electronics in your system, I think your GPS, not your autopilot, is your problem. GPS only CALCULATES your direction of travel. The GPS signal only allows its electronics to figure out your position every second. That display that says your boat is pointed 085 degrees is only a guesstimate of the GPS electronics because it looked at the last few seconds of where you've been and where you are....a little 085 from where you were a second ago. At low speed, a GPS is damned near USELESS as a compass input for the autopilot to follow and shouldn't be used. Too many sailboats try to autopilot in poor wind conditions with the same wandering results because the GPS' idea of direction of travel over ground is wandering, too. What you need for the autopilot is a COMPASS SENSOR. Some are also called Fluxgate Sensors because they use a solid state magnetic field sensor, not a real compass. This device will tell your autopilot which direction the boat is pointed in EVEN AT ZERO MPH, always telling the autopilot to follow a MAGNETIC COURSE from its information, not a wandering GPS course from lack of information. Under 3-4 knots, the GPS is useless as a directional compass sense device because of its calculated guess. Use a real Compass Sensor. Most good autopilots have at least a Fluxgate magnetic sensor as part of their package. Unfortunately, most installations pay way too little attention to the fluxgate's mounting position way too close to magnetic objects mounted "out of sight" in lockers full of magnetic junk and CURRENT CARRYING DC POWER WIRING, which always radiates a strong magnetic field, which drags off the fluxgate or compass sensor's calibration in some odd fashion. The magnetic sensor, whether fluxgate or real compass, needs to be near the CG of the boat's axii, all 3 of them. It needs to be away from all power wiring carrying any kind of appreciable DC CURRENT and away from ALL MAGNETIC OBJECTS, anything made of steel or brass. That's a pretty tall order in a small boat, but very necessary to maintain compass course accuracy at very low speeds. On a rolling pitching boat, the solid state compass sensors are much better than the mechanical ones, which get moving around from the motion and give false readings. It's also best to get one that's "self compensating", one that you simply turn in a circle a few times, slowly, and it makes its own compensation chart which it stores to make more accurate fixes. http://www.maretron.com/products/ssc200.php just as an example..... |
Autopilots
On Sat, 26 Apr 2008 12:19:00 -0400, "Gregory Hall"
wrote: Just what the world needs - another autopilot jetboat jerk who hasn't a clue as to how to safely operate a boat blasting around the water becoming a big nuisance and even larger menace to all concerned. Take your autopilot, and overgrown Jetski for that matter, and shove it up your ass! C'mon Gregory, Why don't you tell him how you REALLY feel? -- Calling an Illegal Alien an "Undocumented Worker" is like calling a Crack Dealer an "Unlicensed Pharmacist" |
Autopilots
On Sun, 27 Apr 2008 03:57:55 +0000, Larry wrote:
away from ALL MAGNETIC OBJECTS, anything made of steel or brass. Since when is brass magnetic? Casady |
Autopilots
Edgar wrote:
You need an autopilot where you can alter the amount of response to a given course deviation. At trolling speeds you need much more rudder angle to correct a deviation than you would at higher speed. However, if you are trolling rather than maintaining course to a destination you ought to be able to accept a greater amount of yawing about the set course anyway. Frankly, I knew that - can you suggest one? Thanks. -- Larry rapp at lmr dot com |
Autopilots
Gregory Hall wrote:
Just what the world needs - another autopilot jetboat jerk who hasn't a clue as to how to safely operate a boat blasting around the water becoming a big nuisance and even larger menace to all concerned. Take your autopilot, and overgrown Jetski for that matter, and shove it up your ass! -- Gregory Hall Gregory, Why don't you come tell me that personally. I live at 1 Indian Trail, Colebrook, New Hampshire and we can talk about this face to face. Lets see if your courage extends that far. -- Larry rapp at lmr dot com |
Autopilots
The autopilot I had used a fluxgate compass. The trolling problem was
the result of incorrect response. It would overcompensate at low speeds because of the amount of time it took between issuing a command (it turned the wheel which directed the jet) and the boat moving. There was no rudder feedback nor could it have been added easily. While there were multiple levels of sensitivity which could be set, none of them worked at low speed with the result that the craft overcompensated. I think the unit was a Raymarine Sportpilot. Normally, one mounts the fluxgate compass as close to the bow as possible, but (naturally) away from anything ferrous like an anchor. The only purpose of a GPS might be to plot a long course, but, as I said, the main reason for adding an autopilot would be for trolling single-handed. I've been boating for over 50 years, and have sailed all around the Carribean, so I'm not a novice. I've owned boats from 14 to 38 ft. and am an EE so don't be afraid to get technical. -- Larry rapp at lmr dot com |
Autopilots
"Larry" wrote in message
... Gregory Hall wrote: Just what the world needs - another autopilot jetboat jerk who hasn't a clue as to how to safely operate a boat blasting around the water becoming a big nuisance and even larger menace to all concerned. Take your autopilot, and overgrown Jetski for that matter, and shove it up your ass! -- Gregory Hall Gregory, Why don't you come tell me that personally. I live at 1 Indian Trail, Colebrook, New Hampshire and we can talk about this face to face. Lets see if your courage extends that far. -- Larry rapp at lmr dot com You're joking. He and his companions are cowards and liar. Maybe you're just being mean, since I'm sure that it's obvious who and what they are. Shame on you Larry! -- "j" ganz @@ www.sailnow.com |
Autopilots
"Larry" wrote in message ... Edgar wrote: You need an autopilot where you can alter the amount of response to a given course deviation. At trolling speeds you need much more rudder angle to correct a deviation than you would at higher speed. However, if you are trolling rather than maintaining course to a destination you ought to be able to accept a greater amount of yawing about the set course anyway. Frankly, I knew that - can you suggest one? Thanks. -- Larry Sorry, Larry-I did hesitate a bit before posting that in view of your electrical expertise. Cannot suggest a make of pilot that would assist you as my last one was a wind vane. Now however I have got a Simrad wheel pilot which was very good when I used it last season to steer compass courses. However I am now on the point of hooking it into the output from the chart plotter so it can steer me to a waypoint but have just seen your later post about the uselessness of GPS based pilots at low speeds and since I have a sailboat it looks as if this will not help me in light winds, so maybe I will leave things as they are. It has a good fluxgate compass which you calibrate by steering in slow circles a couple of times and, best of all,.no belts or control lines across the cockpit. You can control the sensitivity to yawing to minimise battery drain. |
Autopilots
On Sun, 27 Apr 2008 10:27:23 -0400, Larry wrote:
snip LOL what a putz! would you please just get over yourself |
Autopilots
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Autopilots
On Sun, 27 Apr 2008 21:44:36 +0000, Larry wrote:
(Richard Casady) wrote in : Since when is brass magnetic? Casady ***** http://www.kayelaby.npl.co.uk/genera...2_6/2_6_6.html This helpful table compilation from NPL confirms that brass is essentially non magnetic, as it happens. Brian W |
Autopilots
On Sun, 27 Apr 2008 17:06:41 -0500, Brian Whatcott
wrote: On Sun, 27 Apr 2008 21:44:36 +0000, Larry wrote: (Richard Casady) wrote in t: Since when is brass magnetic? Casady ***** http://www.kayelaby.npl.co.uk/genera...2_6/2_6_6.html This helpful table compilation from NPL confirms that brass is essentially non magnetic, as it happens. I tried to follow the link and got the runaround. Thank you for getting there and giving us a report. Maybe there is somthing wrong with the SSSW [Suck****SoftWare]. Casady |
Autopilots
Roger Long wrote:
"Edgar" wrote Sorry, Larry-I did hesitate a bit before posting that in view of your electrical expertise. I think this is a different "Larry" than our regular poster from Charleston SC. Larry (#2), it would help avoid confusion if you added an initial or something to you posting name. -- Roger Long Sorry. There is another Larry who posts fairly regularly in rec.boats.electronics. I am not him! Hows's this? I know I'm going to forget. I've been using this name since 1985 - yes, I'm older than dirt! I'm from NH, btw, originally from Long Island, New York. -- Larry R rapp at lmr dot com |
Autopilots
Capt. JG wrote:
"Larry" wrote in message ... Gregory Hall wrote: Just what the world needs - another autopilot jetboat jerk who hasn't a clue as to how to safely operate a boat blasting around the water becoming a big nuisance and even larger menace to all concerned. Take your autopilot, and overgrown Jetski for that matter, and shove it up your ass! -- Gregory Hall Gregory, Why don't you come tell me that personally. I live at 1 Indian Trail, Colebrook, New Hampshire and we can talk about this face to face. Lets see if your courage extends that far. -- Larry rapp at lmr dot com You're joking. He and his companions are cowards and liar. Maybe you're just being mean, since I'm sure that it's obvious who and what they are. Shame on you Larry! You're right, Cap'n. Normally, I just ignore children going through puberty, but this morning he just pushed the right buttons and I felt he needed to be taught a physical lesson if he had the stomach for it. As you surmised, he didn't. I'll go back to ignoring! -- Larry R rapp at lmr dot com |
Autopilots
Roger Long wrote:
"Edgar" wrote Sorry, Larry-I did hesitate a bit before posting that in view of your electrical expertise. I think this is a different "Larry" than our regular poster from Charleston SC. Larry (#2), it would help avoid confusion if you added an initial or something to you posting name. -- Roger Long Actually, Roger, I'm a retired electrical engineer so I do have a bit of a background in electronics. The autopilot I used had no sensor for speed. Does any? It would seem to me that there needs to be one because response to the wheel is proportional to your speed underway. -- Larry rapp at lmr dot com |
Autopilots
Bigfoote wrote:
"Larry" wrote in message ... Time for a yearly update. I had a Bombardier Utopia - an 18' jet-powered runabout that I added an autopilot to, but while it did work at higher speeds, it failed miserably for trolling and fishing in general. Last year I sold it and bought a center console Cobia, a 21' with a 150 hp Yamaha outboard. I added a 15 hp (smallest I could get without ordering) Suzuki outboard to use as a trolling motor. It is tied, mechanically, to the larger Yamaha and sips fuel from the same large tank. It works pretty well, and steers a straight course with no hands on the wheel. Still, I'd like to add an autopilot IF (and only if) it can operate at trolling speeds (about 1 knot or 1.5 mph). ComNav makes a few units which look like they'd work, but I'd like to hear that from someone other than the manufacturer or salesman, preferably someone who owns one. The boat is equipped with a Garmin 540 combination fishfinder/GPS chartplotter which issues NMEA sentences. -- Larry rapp at lmr dot com Raymarine Sportpilot. It is a wheel mount unit and may not fit but I have had one on an old Slickcraft for 13 years and it is still doing the job trolling for salmon on lake Michigan about 200 hours a year. Did have to replace the electronic compass module once but at a very reasonable price. Even accepts waypoint data from my old Garmin GPS/Plotter. Biggest problem if it fits the wheel is where to mount the compass at lest 3 feet from any large metal mass (i.e. engine). Ideal is low and to the rear to minimize roll and pitch effects on compass but not easy in a small boat. Wow, that is really interesting. I think that is what I used on the Utopia. Perhaps it was because it was a jet boat and very slow to respond at trolling speeds. Interesting. Btw, the reason for getting a jet boat was to eliminate the propeller. It could navigate in very shallow water (so long as there were no weeds and not a lot of mud) but it made an awful boat for fishing. Did you have any kind of rudder sensor? I realize you probably have an outboard, but trolling is really slow - the fact that it works is really significant to me. Also, you put the compass in the rear - I tried it up by the bow and amidships, I could not have put it in the stern as that's where the engine was. -- Larry R rapp at lmr dot com |
Autopilots
On Sun, 27 Apr 2008 21:44:36 +0000, Larry wrote:
(Richard Casady) wrote in : Since when is brass magnetic? Casady http://www.kayelaby.npl.co.uk/genera...2_6/2_6_6.html That website has nothing to say. It lists magnetism in a table of contents but when you click on it, it goes back to a previous table of contents. There seems to be nothing there. Casady |
Autopilots
Larry wrote:
Roger Long wrote: "Edgar" wrote Sorry, Larry-I did hesitate a bit before posting that in view of your electrical expertise. I think this is a different "Larry" than our regular poster from Charleston SC. Larry (#2), it would help avoid confusion if you added an initial or something to you posting name. -- Roger Long Actually, Roger, I'm a retired electrical engineer so I do have a bit of a background in electronics. The autopilot I used had no sensor for speed. Does any? It would seem to me that there needs to be one because response to the wheel is proportional to your speed underway. No, I think they just use the old double-angle-off rule of thumb. -- (remove the X to email) Now just why the HELL do I have to press 1 for English? John Wayne |
Autopilots
Richard Casady wrote:
On Sun, 27 Apr 2008 21:44:36 +0000, Larry wrote: (Richard Casady) wrote in t: Since when is brass magnetic? Casady http://www.kayelaby.npl.co.uk/genera...2_6/2_6_6.html That website has nothing to say. It lists magnetism in a table of contents but when you click on it, it goes back to a previous table of contents. There seems to be nothing there. Casady It showed magnetic susceptibility of brass as 1, steel as 150. Less than 1% as magnetic as steel? Richard |
Autopilots
On Sun, 27 Apr 2008 21:13:31 -0500, cavelamb himself
wrote: http://www.kayelaby.npl.co.uk/genera...2_6/2_6_6.html /snip/ It showed magnetic susceptibility of brass as 1, steel as 150. Less than 1% as magnetic as steel? Richard Well, THAT was an interesting reading of the data! How would you respond if I said both copper and zinc were less magnetic in terms of susceptibility than for example the transparent plastics? Ah, yes but there might be minor iron inclusions in a brass casting? Yeppers! Or in a bronze casting. Or a cxopper casting. Or in an aluminum casting.... :-) Regards Brian W |
Autopilots
On Mon, 28 Apr 2008 06:03:18 -0400, "Roger Long"
wrote: I would imagine from the name that they adjust their response according to the speed of the heading change which should produce similar results to a speed input. Yes, no speed input, just rate of change. |
Autopilots
On Sun, 27 Apr 2008 10:49:18 -0400, Larry wrote:
The autopilot I had used a fluxgate compass. The trolling problem was the result of incorrect response. It would overcompensate at low speeds because of the amount of time it took between issuing a command (it turned the wheel which directed the jet) and the boat moving. There was no rudder feedback nor could it have been added easily. While there were multiple levels of sensitivity which could be set, none of them worked at low speed with the result that the craft overcompensated. I think the unit was a Raymarine Sportpilot. Normally, one mounts the fluxgate compass as close to the bow as possible, but (naturally) away from anything ferrous like an anchor. The only purpose of a GPS might be to plot a long course, but, as I said, the main reason for adding an autopilot would be for trolling single-handed. I've been boating for over 50 years, and have sailed all around the Carribean, so I'm not a novice. I've owned boats from 14 to 38 ft. and am an EE so don't be afraid to get technical. Give it a rudder so it can become the happy little second-order system it was born to be. |
Autopilots
Roger Long wrote:
I haven't given much thought to the innerworkings of autopilot control circuits. I've never heard of a speed input but do know that "rate based" autopilots are considered better than "heading based" units on aircraft. I would imagine from the name that they adjust their respons according to the speed of the heading change which should produce similar results to a speed input. You might be interested in this bit of electronics tinkering I did last fall: http://home.maine.rr.com/rlma/ST1000mods.htm -- Roger Long Very clever, Roger. My unit, I believe it was a Sportpilot, used a motor to drive the wheel. It must have been fitted with limit switches as the motor didn't seem to overheat, but the rate of response was, as I said, too slow when trolling. I thought about going into the controller and adjusting it, probably through software, but it probably use a surface mount processor and it was just too much work. I called Raymarine or whoever made the thing and they weren't interested in helping. As I said earlier, I sold the boat and got something a lot better (at least in my judgment). I could live without an autopilot now (and I may), especially since this boat tracks well, but I can never leave well enough alone... -- Larry rapp at lmr dot com |
Autopilots
Wayne.B wrote:
On Mon, 28 Apr 2008 06:03:18 -0400, "Roger Long" wrote: I would imagine from the name that they adjust their response according to the speed of the heading change which should produce similar results to a speed input. Yes, no speed input, just rate of change. Then they cannot differentiate between a massive craft which isn't all that maneuverable to start with, and something handier that is just moving slowly. Oh well... -- Larry R rapp at lmr dot com |
Autopilots
Goofball_star_dot_etal wrote:
Give it a rudder so it can become the happy little second-order system it was born to be. Well, you can't add a rudder to a jet boat. I could have connected the sensor to the tube used to steer the craft, but since the the entire coupling was underwater, it would have been quite a production and I still don't know that it would have worked correctly. -- Larry R rapp at lmr dot com |
Autopilots
On Tue, 29 Apr 2008 10:53:50 -0400, Larry wrote:
Goofball_star_dot_etal wrote: Give it a rudder so it can become the happy little second-order system it was born to be. Well, you can't add a rudder to a jet boat. Try to remember that you sold that boat last year and want to control a boat with a 15 hp Yamaha outboard at "trolling speeds (about 1 knot or 1.5 mph)"!! with an autopilot which expects a certain (range of) yaw rate proportional to the control input, not a pig dominated by small forces and relatively large moment of inertia. |
Autopilots
Goofball_star_dot_etal wrote:
On Tue, 29 Apr 2008 10:53:50 -0400, Larry wrote: Goofball_star_dot_etal wrote: Give it a rudder so it can become the happy little second-order system it was born to be. Well, you can't add a rudder to a jet boat. Try to remember that you sold that boat last year and want to control a boat with a 15 hp Yamaha outboard at "trolling speeds (about 1 knot or 1.5 mph)"!! with an autopilot which expects a certain (range of) yaw rate proportional to the control input, not a pig dominated by small forces and relatively large moment of inertia. Yes, I understand, but how would you add a rudder to an outboard? Or do you mean use the steering mechanism as a rudder? (actually, the big engine is a Yamaha, the 15 hp is a Suzuki) I would assume that any autopilot would net out yaw, but I don't know and don't want to pay all outdoors to find out. Are you saying it's a large factor? I fish northern New England lakes - yaw isn't a big factor. Also, I am not a commercial fisherman - I fish for fun. If the weather goes south, I generally head in. -- Larry R rapp at lmr dot com |
Autopilots
On Tue, 29 Apr 2008 17:44:52 -0400, Larry wrote:
Goofball_star_dot_etal wrote: On Tue, 29 Apr 2008 10:53:50 -0400, Larry wrote: Goofball_star_dot_etal wrote: Give it a rudder so it can become the happy little second-order system it was born to be. Well, you can't add a rudder to a jet boat. Try to remember that you sold that boat last year and want to control a boat with a 15 hp Yamaha outboard at "trolling speeds (about 1 knot or 1.5 mph)"!! with an autopilot which expects a certain (range of) yaw rate proportional to the control input, not a pig dominated by small forces and relatively large moment of inertia. Yes, I understand, but how would you add a rudder to an outboard? Or do you mean use the steering mechanism as a rudder? (actually, the big engine is a Yamaha, the 15 hp is a Suzuki) I can see two options. The first is to attach a foil to the 'small' outboard eg. http://www.freepatentsonline.com/3991700.html This would be steered through your existing arrangement with or without an autopilot. I assume that this small outboard can be raised when not in use, removing the rudder from the water, but if it is robust enough could be left in the water at speed.. The disadvantage of this scheme is the large load on the autopilot of having to control both motors though the steering mechanism. The second option would be an auxiliary rudder similar to a typical sailing dinghy rudder with a lifting blade to be used only when trolling. This could be large enough to do the required job but quite light and weak. If the rudder/boat response is good enough the cheapest autopilot could be attached and used just for low speeds, with a remote control if required. This arrangement would be a nuisance and likely be damaged at speed so needs to be retracted then. I would assume that any autopilot would net out yaw, but I don't know and don't want to pay all outdoors to find out. Are you saying it's a large factor? No, I mean that most boats at normal speed turn more or less like a car, with a turning circle radius that reduces with helm movement. The assumption is that autopilots are designed for typical boats behaving in this way. Observing autopilot behaviour, they seem to move the helm in proportion to the error, although there is also a dead-band, some integration of error and some damping involved. It seems they would assume a rate of turn proportional to the error signal and actuator movement whereas a jet or outboard at low speed produces a very small transverse thrust in response to the angular error signal, causing angular acceleration that increases the rate of turn with time. It seems a better plan to try to fix the boat's low speed steering than to expect a control system to cope with this. You need the gain of the factors that relate angular heading error to the boat's rate of turn (yaw rate) to be more or less constant and within the bounds of the autopilot design, then all should be well. You don't want the error integating up because nothing has happened yet! I fish northern New England lakes - yaw isn't a big factor. Also, I am not a commercial fisherman - I fish for fun. If the weather goes south, I generally head in. I don't bother to go out sailing unless there is some decent wind and waves.. |
Autopilots
On 2008-04-27 20:46:09 -0400, Larry said:
The autopilot I used had no sensor for speed. Does any? It would seem to me that there needs to be one because response to the wheel is proportional to your speed underway. Haven't been paying attention to this thread, but my tiller AP will "read" some NMEA speed sentence and the swing can be adjusted. -- Jere Lull Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/ Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/ |
Autopilots
Bigfoote wrote:
Raymarine Sportpilot. It is a wheel mount unit and may not fit but I have had one on an old Slickcraft for 13 years and it is still doing the job trolling for salmon on lake Michigan about 200 hours a year. Did have to replace the electronic compass module once but at a very reasonable price. Even accepts waypoint data from my old Garmin GPS/Plotter. Biggest problem if it fits the wheel is where to mount the compass at lest 3 feet from any large metal mass (i.e. engine). Ideal is low and to the rear to minimize roll and pitch effects on compass but not easy in a small boat. Would you please describe your Slickcraft? I think I had a Raymarine Sportpilot, it may have changed, but perhaps it can be made to work. Thanks! -- Larry R rapp at lmr dot com |
Autopilots
Goofball_star_dot_etal wrote:
I can see two options. The first is to attach a foil to the 'small' outboard eg. http://www.freepatentsonline.com/3991700.html This would be steered through your existing arrangement with or without an autopilot. I assume that this small outboard can be raised when not in use, removing the rudder from the water, but if it is robust enough could be left in the water at speed.. The disadvantage of this scheme is the large load on the autopilot of having to control both motors though the steering mechanism. The steering is hydraulic. I haven't done any testing, but it doesn't seem like much of a load. I can disconnect the arm which connects the two motors - the force required to turn the wheel doesn't change very much. In the case above, if I read the link correctly, the "rudder" is nothing but a flat plate behind the propellor. And, yes, the motor can be raised. I don't understand how the "rudder" adds anything as steering is still accomplished by moving the motor. The only thing added here is direct feedback from motor pointing (via steering). That must be important for the system to function as it was suggested by the Sportpilot (if that's what it was). I don't see what it adds as all it would do is provide an indication of potential slack or "play" in steerage. The second option would be an auxiliary rudder similar to a typical sailing dinghy rudder with a lifting blade to be used only when trolling. This could be large enough to do the required job but quite light and weak. If the rudder/boat response is good enough the cheapest autopilot could be attached and used just for low speeds, with a remote control if required. This arrangement would be a nuisance and likely be damaged at speed so needs to be retracted then. I would assume that any autopilot would net out yaw, but I don't know and don't want to pay all outdoors to find out. Are you saying it's a large factor? No, I mean that most boats at normal speed turn more or less like a car, with a turning circle radius that reduces with helm movement. The assumption is that autopilots are designed for typical boats behaving in this way. Observing autopilot behaviour, they seem to move the helm in proportion to the error, although there is also a dead-band, some integration of error and some damping involved. It seems they would assume a rate of turn proportional to the error signal and actuator movement whereas a jet or outboard at low speed produces a very small transverse thrust in response to the angular error signal, causing angular acceleration that increases the rate of turn with time. It seems a better plan to try to fix the boat's low speed steering than to expect a control system to cope with this. You need the gain of the factors that relate angular heading error to the boat's rate of turn (yaw rate) to be more or less constant and within the bounds of the autopilot design, then all should be well. You don't want the error integating up because nothing has happened yet! My understanding of yaw differs from yours. You're probably correct. My understanding of yaw is coupled with pitch and nets out but does provide considerable movement. I _thought_ a fluxgate compass enclosed a gimballed affair with sufficient time constants to do that (net out pitch and yaw). With the Sportpilot, it seemed as though if the time constant of the response curve could have been lengthened, the system would have worked. What I perhaps should have done was to measure the amount of time the boat took to go from one compass point to another (say 45 degrees apart) and compare that with what the current boat does, both at the same speed. Actually, that sounds like a plan and I can still do that as I will be seeing the owner of the Utopia in early July and will have my boat with me. At trolling speeds, if the boat turns substantially faster, then the old system might work - without a rudder! Your explanation makes sense to me, but unless the control electronics are very "smart" that gain has to be variable and it wasn't. Well, there were, as I recall, three steps, but the longest response time wasn't long enough and horrible overcorrection occurred at low speeds. In fact, the longest response was what I had to use at higher speeds. "Bigfoote" seems to indicate that a Sportpilot would work and, as I recall, that was nowhere near as expensive as other units. Of course, you get what you pay for, yada, yada, yada... Thanks! -- Larry R rapp at lmr dot com |
Autopilots
Jere Lull wrote:
On 2008-04-27 20:46:09 -0400, Larry said: The autopilot I used had no sensor for speed. Does any? It would seem to me that there needs to be one because response to the wheel is proportional to your speed underway. Haven't been paying attention to this thread, but my tiller AP will "read" some NMEA speed sentence and the swing can be adjusted. Do you know if reading the NMEA sentences replaces the fluxgate compass or is used for longer range navigation (plotting a course with waypoints). Thanks -- Larry R rapp at lmr dot com |
Autopilots
On 2008-04-30 10:30:07 -0400, Larry said:
Jere Lull wrote: On 2008-04-27 20:46:09 -0400, Larry said: The autopilot I used had no sensor for speed. Does any? It would seem to me that there needs to be one because response to the wheel is proportional to your speed underway. Haven't been paying attention to this thread, but my tiller AP will "read" some NMEA speed sentence and the swing can be adjusted. Do you know if reading the NMEA sentences replaces the fluxgate compass or is used for longer range navigation (plotting a course with waypoints). Thanks I think I should have said "phrase" instead of sentence. I'm a little confused as the speed phrase I'm talking about from the knotlog wouldn't be affected by the direction the boat was pointing. The AP can adjust rudder sensitivity and calculate current set from that speed phrase, as I recall. The input from the fluxgate would have a different phrase (If our AP can take an external one). Our AP calculates a specific-width "lane" between two waypoints, adjusting its heading (against internal or external fluxgate) vs GPS heading depending partially with heading to the next mark, but it's more concerned with getting back into the lane. -- Jere Lull Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/ Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/ |
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