Sunday, February 17, 2013

Stabilize the mast with two paravanes!

Today (Feb 17, 2013) I think I have just about figured out the key part for my first solar boat experiments. I will be converting my Macgregor 26 sailboat to solar/electric. The real trick is how to make a slow boat without sails not roll so badly as to make all the crew sick. My idea today is a water-kite/paravane on each side that is attached to the top of the mast and designed so they stay at the surface maybe 50 feet to each side. 
 The top side of the paravane will have a float.  If this is under the water the drag will cause the paravane to turn up.  The bottom of the paravane will have something to cause drag, but less than the float, so that if the float goes out of the water  the paravane will turn down into the water.  There will be some kind of tail so that it does not turn too fast.
The boat is about 8 feet wide, so 4 foot radius.  The top of the mast is about 35 feet above the water.  So the leverage some force at the top of the mast has, compared to someone standing on the edge of the boat is 35/4 = 8.75.  So 100 lbs of force sideways at the top would balance 875 lbs on the edge of the boat.  Now the rope to the paravane will have an angle on it so it will be less.  The point is that a small force from the paravane can make a big difference because of the long lever from the mast.
I can't find anyone else who has tried exactly this.    It is very similar to the flopperstoppers used by trawlers but these will pull to the sides instead of just down.  Then we don't need special poles on each side and can just use the top of the mast.  As the mast gives me more leverage and my boat is much lighter than a trawler, the forces I will be dealing with are far less.  However, I will be moving slower than a traweler so my paravanes may not be smaller, but they won't have to be so strong.  The military minesweeper paravanes were towed off to each side, and automatically kept to the sides without any poles, but not for stability.  There is a speed sailer that used a paravane from the top of a mast but only on one side and while sailing.  So there are enough similar things that I think I have a good chance of making paravanes  work for stabilizing my solar electric boat.
I am going to use the Minn Kota RT160EM which mounts onto the engine.  This is about 3.5 Hp.  Since the boat is so light I think this will do for moving slowly (I am guessing 4 MPH but will be very interested in real data).
I plan to start with two rugged solar panels from Commet Systems and just let them charge the batteries for  6 days and then play on the weekend.  If this works as well as I think then I will probably get some lightweight solar panels and put up a bunch more.
 The danger is that the paravanes might go bad and cause the boat to tip.  With the electric motor we won't be going fast, so I think even if there is a glitch we will be fine.   Will experiment with caution.  
I think a simple paravane can work well enough, but the idea of adding a computer to control fins on the paravane is another possibility.  A simple paravane going up and down in waves will cause some pulling on the mast.  A smart paravane could do a better job. 
The paravanes could be radio controlled, much like a toy boat really.  Just that a string is pulling it through the water.   If I have one son driving the toy on the right and another driving the one on the left they could compensate for waves and probably keep the mast straight up and down.  It would be a fun game for awhile.  Then would want to get a computer to drive the two paravanes.

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