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Old Jan 29, 2011, 10:52 AM
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United States, MN, Brainerd
Joined Oct 2004
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Still thinking...

Quote:
Originally Posted by Brooks View Post
Ingenious DanL. Comments:
1. As you move the drum, either athwartships or fore&aft, the drum must be turning, or the tension of the braces must be changing (leeward brace becoming more taut for f&a movement, more slack for side to side movement). To remove slack from the windward brace, yet not affect length(=tension) of the leeward brace, the path of the non-turning drum must be diagonal, not simply X or Y. The drum is turning. That's what provides the force to move the servo against the force of the bungee/spring. The servo does not move along the guide unless the drum turns and changes the overall length (L port brace + L stbd brace). The amount of rotation vs the distance moved to take up any overall slack balance out.

Simply moving the drum along only X or Y axis is not sufficient to balance the slack, you need freewheeling of the drum. If you did not notice freewheeling, then the braces may have slipped on the drum, or the leeward brace tightened/slackened w/o your noticing. The test system had very little play, and the braces were securely tied into the drum. I checked alignment after each rotational adjustment to be sure sytem geometry didn't shift (thats why all the maskng tape marking the key geometry points) Still, there surely could be somethinI missed...Something needed to happen, at any rate. Freewheeling in both directions (CW and CCW) is not possible with a typical winch setup (it's not integral to the winch design because it would not be desirable for most winch setups).Lightbulb just went on (I think). The "freewheeling" doesn't occur in the rotation of the drum, it occurs in the rotation of the yard! As one brace is pulled tight, and slack develops in he opposite brace, the bungee pulls - changing L total, until the yard rotates and both braces are equal tension.

2. The diagonal movement of the non-freewheeling winch drum could be designed in, I imagine, either with a pre-calculated arcing track (along the diagonal) or with self-adjusting X&Y axis bungees. The generation of brace slack is non-linear, thus the track of the winch would have to be an arc along the diagonal, not a straight diagonal.

3. The prototypical way to accommodate the brace-length problem is the Jarvis winch. The winch drums for each brace were cone shaped, not cylindrical. The port brace cone was the mirror image of the starboard brace cone. It's a hard problem, to be sure. Even the Jarvis winches made provision a) for onsite setup (it proved impossible to design the drums' cone shapes perfectly in the office) and b) for fine-tuning adjustment of braces manually; that is, the Jarvis winch was usually unable to completely control slack, you still had to take a short pull on one or the other braces.

4. The slack of the windward brace is of aesthetics concern to modelers, but is not of great operational concern to modelers, in my experience. On a beat, excess slack in the windward brace merely means that the wind presses the yards to swing as far as the standing rigging and yard crane allow, which is usually desirable for good performance to windward. With no interferring standing rigging, though, especially in the topgallants and above, the yards can over-rotate, setting the sails perpendicular to the wind (which would be very undesirable); But merely hauling back on the joysticks a bit solves the over-rotation problem. Or you can install my "jaw-jammers" to stop upper yard over-rotation. At sea, both windward and leeward braces are kept taut during the tacking maneuver, but then the windward brace is slackened slightly once the tack is completed. This is to reduce strain on the rigging (and the yards) as the ship rolls&pitches and the masts sway a bit.
To my thinking, you are solving a problem of aethetics, not operation. Well worth doing, of course, I applaud your efforts. Some aesthetics, but really also necessary functionally. A slack brace leads to the brace potentially dropping out of the drum flange. Early on, I had all sorts of tangle problems. That's how I got to al the slack compensation in the first place. The other problem is the flaky winds. As the wind swirls - typical - we rarely see steady wind - the yards would slap around silly if they weren't constrained in both rotational directions. I fairly often see the "slap" that would cause a slack braced sail to come around.Keep up the experimenting, Well Done.
Brooks, thanks for the exensive comments. I still haven't solidified my understanding of what I observed. Your comments really help to reach an understanding of this.
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Last edited by DanL; Jan 29, 2011 at 12:12 PM.
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