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Old 03-05-2018, 17:33   #46
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Re: Self Steering Off Shore

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Originally Posted by ZULU40 View Post
whenever someone speaks like this its time to step in

this is straight out engineering

a linear drive that can exceed the rudder force and do so in a timely manner will hold a course, examples are plentiful when seas and weather are slight. The problem is the retailers offer 'popular' hardware that is poorly designed, even more poorly built and too slow to react.

that can be changed, and in lesser known drives already has.
Industrially the speed of linear drives is miles in front of the simple screw jacks most offer for auto tillers. Speed = faster correction and less power consumed.

Unless it is mapping upcoming waves it is still reacting with a lag.

The mechanical link from wave to servo rudder to tiller to rudder is instantaneous. It has nothing to do with the autopilot whatsoever.

Now I remember why I quit coming here.

Reply all you like, step right in, I won't be back.




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Old 03-05-2018, 18:50   #47
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Re: Self Steering Off Shore

Quote:
Originally Posted by ZULU40 View Post
whenever someone speaks like this its time to step in

this is straight out engineering

a linear drive that can exceed the rudder force and do so in a timely manner will hold a course, examples are plentiful when seas and weather are slight. The problem is the retailers offer 'popular' hardware that is poorly designed, even more poorly built and too slow to react.

that can be changed, and in lesser known drives already has.
Industrially the speed of linear drives is miles in front of the simple screw jacks most offer for auto tillers. Speed = faster correction and less power consumed.
I think you mis-understand what he is saying an autopilot cannot do as well as a wind vane.

On a broad reach for example, wave action against the paddle will effectively cause the vane to "slalom" the boat in a very effective manner through the waves. The issue with respect to APs has nothing to do with the capability of the drive unit, it's a function of the algorithm in the AP computer and what it's capabilities are.

Modern APs that are designed specifically for sailing (B&G for example) are exceedingly capable, and can steer through waves in this manner very well, bit it's arguable that pendulum wind vanes do a better job in some circumstances.
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Old 04-05-2018, 18:58   #48
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Re: Self Steering Off Shore

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Old 04-05-2018, 22:51   #49
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Re: Self Steering Off Shore

I did 53,000 nautical miles around the Pacific. I used a windvane with a simple Fischer linkage to a moderately balanced independent rudder, hung in a bumpkin fitted outboard of the stern. It steered me for 52,000 of those miles, the other 1000 I was motoring.


I then spent 8 years running tourist boats on the Great Barrier Reef in Queensland, Australia. These ranged from 50Ft overnight reef charter boats, through island day trip boats to high speed 350 passenger tourist cruise boats. The auto pilot on these were asked to work about 5 hours a day, & usually averaged about 4 of those actually working properly.


For me, for long passages, it has to be the best possible wind vane system.
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Old 05-05-2018, 05:33   #50
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Re: Self Steering Off Shore

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Originally Posted by Custom30 View Post
Unless it is mapping upcoming waves it is still reacting with a lag.

The mechanical link from wave to servo rudder to tiller to rudder is instantaneous. It has nothing to do with the autopilot whatsoever.
Well, for some years already many autopilot computers have quite sophisticated programs which can anticipate wave action and steer pro-actively -- that is, without a lag, so this statement is not true. These pilots use not only HDG data from the compass but also inertial data from the gyro unit like pitch, roll, and ROT, and some of them are even capable of learning. If you tune them right they can work quite well.

But that takes nothing away from your point (which others have also made) about how well wind vanes steer in certain conditions. No doubt some wind vanes will steer better than any electronic pilot in certain conditions.

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Old 05-05-2018, 07:47   #51
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Re: Self Steering Off Shore

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... from the gyro unit like pitch, roll, and ROT, and some of them are even capable of learning. If you tune them right they can work quite well.

But that takes nothing away from your point (which others have also made) about how well wind vanes steer in certain conditions. No doubt some wind vanes will steer better than any electronic pilot in certain conditions.

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I think the point is, the pendulum oar senses yawing when it is dragged sideways through the water and this is critical to their performance. Further, the pendulum oar already helps steer the boat correctly. A simple self steering using a trim tab connected to an air vane doesn't do either.

It is similar to the gyroscope input to the autopilot. The main problem is, it cannot differentiate the rate of change of the gyro the way a computer can, so it will not steer harder at the beginning of yawing and less when the rate of turn is slowing. This means the wind vane will steer in S course.

I think it is definately possible that an electronic autopilot can outperform a wind vane in all cases. The issue is having such a large motor, it's really a lot of power needed in a storm, and probably not even pratical for full-keel boats. With a large motor, power consumption is not efficient in light conditions.

You would want a small motor for typical conditions, and a large one (4x more powerful) for rough ones for best efficiency, or a small autopilot motor for light air, and a wind vane is a great option.
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Old 05-05-2018, 08:24   #52
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Re: Self Steering Off Shore

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You would want a small motor for typical conditions, and a large one (4x more powerful) for rough ones for best efficiency, or a small autopilot motor for light air
Its always possible to use a number of drives mastered by the same system on the same application, some more powerful than others, perhaps some in addition to others

I dont think being pushed off course by some influence such as a wave is all that critical to successful operation, because the boat should come back on course. It could also be that although the hull is yawing and the deviation off course isnt great. You need to look at the wake and watch the compass.

If the AP doesn't keep a boat on course then you simply dont have enough power or actuator speed to maintain a heading. But both are entirely developable options.
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Old 05-05-2018, 09:28   #53
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Re: Self Steering Off Shore

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You would want a small motor for typical conditions, and a large one (4x more powerful) for rough ones for best efficiency
I am not sure this is always true.

For our new boat I wanted a powerful, oversized drive unit. Surprisingly, according to Jefa the larger unit was slightly more power efficient (for the same load) as some of their smaller units.

Of course a less powerful unit will have a lower maximum power draw, but of you look at the power draw for a certain load, do not assume that a smaller unit will be more efficient.

There does seem to be big jump in power requirements when adopting an electric/hydraulic unit as opposed to a pure electric drive, but this is more to do with the different technologies rather than just the size of unit.

In any case, the power consumption of modern electric autopilots is becoming a relatively minor part of the energy budget, at least for larger yachts, although it is worth seeking some of the power efficient units. I would suggest selecting a larger rather than a smaller drive unit if regularly sailing offshore.
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Old 10-05-2018, 14:38   #54
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Re: Self Steering Off Shore

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I am not sure this is always true.

For our new boat I wanted a powerful, oversized drive unit. Surprisingly, according to Jefa the larger unit was slightly more power efficient (for the same load) as some of their smaller units.
If the smaller unit cannot keep up, or is overloaded then yes it will use more power.

In very light conditions with slight force on the rudder, then a smaller unit is typically more efficient mostly due to lower friction of smaller moving parts, but as you say "not always true" it' depends also on the type of rudder and how it is balanced.


In rougher conditions you need more speed. Downwind you need more speed, Upwind you need more torque. If the rudder is not balanced you need more torque..

Cheaper high friction drives do not scale as well over a wide operating range to be efficient since they have the same high friction even when moving slowly or lightly loaded, where a better quality ball-screw will have a wider efficient operating range.

So lots of variables to consider and tradeoffs to make. Typical tillerpilots are really inefficient and finally inadequate above a certain sea state. It's crazy that they rate them by boat weight which like saying a dingy can carry up to 4 people without considering who.
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