Thread: Discussion Atlantic Harbor Tug
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Old Jul 05, 2007, 08:23 PM
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Bozeman, Montana, United States
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You could predetermine the max wind your tug would be able to handle, in a manner similar to figuring out it's ability to haul the Schooner off the sandbank:
1. measure the bollard pull of the tug using a fisherman's scale.
2. measure the windage of the Schooner, ie it's pull on the fisherman's scale, when sitting at anchor at various wind speeds.
3. As long as the windage is less than the bollard pull, the tug should be able to handle the job.

The farther apart the 2 numbers are, the faster the tug will get the tug&schooner combo up to "hull" speed. The hull speed will be reached when the form drag of the 2 hulls plus the windage drag of the 2 boats equals the bollard pull. Once the the thrust and drag vectors are equal, no further acceleration is possible, for the mathematically inclined :-)

As you know, it takes very little force to move something floating in water. Even a pixy tug would be able to move your schooner in still air, provided you gave it enough time to accelerate the combo. The hull speed of the pixy tug combo would be less than that of your tug&schooner because the form drag and windage drag both increase with speed, and the equilibrium point would be lower for the pixy.

A long, slick hull like your schooner's should be towable with little force in still air, I would think. Anyone with a valuable sailboat like your's has an interest in rescue techniques. If you were to figure out the numbers and capability for tug and Schooner, I think we'd all be interested, particularly Phillip so he could put the info in his advertisements.
Even if you find that the tow ablity of your tug is limited to light airs, I would not be too discouraged. Your tug may still perform useful rescue service. For instance, if you lost RC control of the Schooner, you could still sail the Schooner back home by using the tug to turn the Schooner on course by pushing on it's bow. Depending on the sail configuration when the RC crapped out, you might have to wear ship, rather than tack, with the tug's assistance. And your zigzag upwind might not be composed of equal angle legs if your squares are set (since they'd be aback for one set of legs). But even a sawtooth recovery course taking lots of time might be preferable to having to chase the ship downwind to a lee shore.
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Last edited by Brooks; Jul 05, 2007 at 08:40 PM.
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