Rescue of stranded sailing ships
Posted by Brooks on this thread and moved here.
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.
While on the subject of rescue, may I suggest that you install a marker buoy on your Schooner, with a line long enough to reach the surface of whatever water body you are traversing. The buoy could be a freely detaching fitting of some sort, something you'd normally find on deck. The line needn't be strong enough to haul the ship back to the surface, just something strong enough to support a buoy to let you know where to dive to recover the ship. Accidents happen: I read of a guy whose schooner was run down by a paddle boat - it remained floating, fortunately, but if it had sunk, a marker buoy would have been comforting, I bet.
Yes...it would be interesting to know the amount of pull the schooner has and the tug has. I don’t think a fishing scale would be sensitive enough in the lower range needed to gage the force each exerts, at least none of the ones I have will work.
I did devise a marker buoy system for the Privateer Schooner Prince de Neufchatel…but never installed it. The reason being that the small lake I used to sail her in was drained and the only other place I sail her, due to lack adequate launch sites, is in a pond at the park. The pond is only 3 ft deep according to the engineer that built it, so theatrically if she goes down she should still have masts sticking out of the water. The biggest problem with the pond is NO shade trees and as you know…it gets very hot and humid here in Alabama. So…I choose not to sail her right now, opting to work on other boats and sail in another pond nearby that does have lots of shade but no place to launch deep drafted large ships. Another problem is the pond has an island that makes it possible to run aground and is inaccessible, as is one whole side of the pond due to a shallow weedy area. I don’t care to get in the water due to rather large Water Moccasins that I have observed in outings past. The ponds are no fishing, boating or swimming posted and I am the only one I have seen to use RC boats in them. I was told that someone with RC Nitro go fast boats tried to use the ponds, but got run off. They are loud and a problem for the wildlife. These ponds are in a park that contains the Alabama Shakespeare Theater and is one of Montgomery’s tourist attractions. Sooo…if I want to continue to use them, I need to be kind to the ponds and stay low profile with wind power and slow electric boats.
One other solution I thought of to rescue my ship is to attach a line to the tug, the other end in my hand and try to encircle the schooner (if it runs aground) release the line from the tug and pull the ship by hand off of the shoals. The line would need to have a small treble hook to snag the tow line as I cross back over it. I just need enough force to get the ship free again. It might work?
So…I feel like I will have several systems in place the next time I go sailing the schooner and not have to worry about the shoals any more.
For a look at my tug tow line release system, go to the thread posted above.