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  #1  
Old 01-26-2013
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Autopilot dumb question

OK, let's picture two boats, one that weighs 10,000 lb and one that weighs 40,000 lb. Lets assume that each sails well (ie balances well and does not have a heavy helm), and that the steering wheels are the same diameter, ie similar mechanical advantage. The smaller boat has a wheel mounted autopilot which works fine. Why would the same autopilot not work with the bigger boat since the steering effort is the same for both boats? BTW, we have a below deck pilot.
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Old 01-26-2013
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Re: Autopilot dumb question

Often wondered that myself.. the steering effort would seem to be the limiting factor, not the displacement. I've sailed smallish boats that would pull you off the seat, and others that are fingertip steering all the way.. go figure.
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Maybe it was not as dumb a question as I thought.
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Re: Autopilot dumb question

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Originally Posted by killarney_sailor View Post
Maybe it was not as dumb a question as I thought.
... I dunno... I had the same thought so it could easily be!!
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Re: Autopilot dumb question

Wheel pilots are designed for boats the don't have the the space or access to below decks. The motor and workings are exposed to the elements cutting down on the dependability & longevity. The tiller arm on a below deck system is about a foot long attached to the quadrant. If you ever had to hand steer with a E tiller all you questions would be answered. Recently had to up grade a boat that had an undersized hydraulic linear drive because the dealers speced. the next size down to save money the first down hill ride in 8fters reviled the problem.
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Re: Autopilot dumb question

Quote:
Originally Posted by killarney_sailor View Post
OK, let's picture two boats, one that weighs 10,000 lb and one that weighs 40,000 lb. Lets assume that each sails well (ie balances well and does not have a heavy helm), and that the steering wheels are the same diameter, ie similar mechanical advantage. The smaller boat has a wheel mounted autopilot which works fine. Why would the same autopilot not work with the bigger boat since the steering effort is the same for both boats? BTW, we have a below deck pilot.
In my world...
the 10,000 lb boat have a small wheel and
the 40,000 lb boat have a much larger wheel (and a larger quadrant)

But even if they had the same steering system the heavier boat need more force on the wheel when it get's a little bit off balance. The AP must be sized to handle this also.
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We don't have a particularly large wheel on our Bristol (40,000 lb loaded for cruising) but it is quite easy to steer even in heavy conditions and strong winds. We have been out in Force 10 and steering effort was the least of our worries. It is no harder to steer than much smaller boats I have owned and actually easier than some. I assume this is a function of the inherent good design of the boat (thank you Mr Hood), but also that the steering system is configured to make the steering effort appropriate.

I certainly understand that a wheel-mounted unit is more exposed to the weather and won't be as reliable, but that is a different discussion.
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Old 01-26-2013
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Re: Autopilot dumb question

If both boats, the 10 000 lbs and the 40 000 lbs, were directly steered with the reserve tiller the difference in needed force would be substantial. When the boat is balanced no force is required but when a wave puts the boat out of the way the mass of the heavier boat requires a lot more effort to put it back in course.
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I would agree with PCP if we are talking about steering with the emergency, or indeed any, tiller, but the question I asked was about wheel steering. There is obviously mechanical advantage built into wheel steering that can mean that it is as easy to steer the bigger boat (perhaps even easier). Am I missing something?
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Re: Autopilot dumb question

I think sometimes the 'easier' steering on the larger boat can come from the increased mechanical advantage of a larger wheel.. since the wheelpilot's drive gear wheel is the same size for all perhaps that's where it all comes into play. Also seems that hydraulics vs chain/cable vs link/lever systems would another be a consideration.
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