Wednesday, April 13, 2011

A wet finger in the air

That's as good as it gets here on Eolian for detecting the wind direction right now.  And on a vehicle that depends on the wind for propulsion, knowing its exact direction is important!  You may remember our fat bird incident, where a gravitationally-challenged bird sat on our windvane and broke it off.  So we are down to a wet finger in the air here.

Masthead transducer,
sans wind vane
I removed the transducer from the masthead and taped over the connections up there.  So here is what it looks like.  If you turn that dark grey disk on the top, it makes the cockpit display turn.  So all I have to do is put a wind vane on that grey disk.

But where?  Since the cockpit display only allows for +/- 15° calibration adjustment, it is important to get the vane on there in the correct orientation.  Rather than climb to the masthead and try to adjust it up there with Jane in the cockpit below telling me when I have it turned dead ahead (too much drama, aside from climbing the mast again), I made up a patch cable and hooked the transducer up directly to the cockpit display.  The tricky part of that task was to make connections to each of the 6 pins in the connector on the transducer, pins which are very close together.

Alternate use for DB9 connectors
I didn't want to solder anything to them (even if I could) because then there would be a problem cleaning off the solder well enough to allow the pins to enter the masthead connector.  I finally settled on using the female connectors sold for use in computer connectors.  These come attached to the web on which they are fabricated.  I pressed an old RJ45 ethernet cable into service for the actual wiring (I only needed 6 of the 8 wires), and soldered a connector on each.  These were easy to push onto the connector pins without shorting between them (sorry this important part of the picture is out of focus).

Now I could turn the shaft on the transducer back and forth to get the display exactly centered.  And then I marked things to retain the results of this work.

OK, so now I know how to orient the wind vane.

What wind vane?  I don't have one anymore.  Da%$# fat bird!

It turns out that a 1" PVC pipe cap is just about the perfect size to fit over the body of the transducer, reaching down the sides a distance to protect against water intrusion, and making a pretty tight fit around it.  So I started with that as a base.

In balance?
Next I drilled a 1/8" hole across the PVC fitting and added a 1/8" brass rod.  Then I cut a vane from some sheet brass to what was a pleasing shape of adequate size and soldered it to the rod.  Finally, I threaded the other end of the rod to accept a counterweight (this thing has to balance, otherwise the reading will change when the boat heels).  The counter weight is a 3" length of 3/8" brass rod, drilled and threaded on one end.  I shaped the front end by chucking it in my drill press and applying a file.  (Here, I am getting the rough balance point by balancing it upside down on the handle of a hammer.  Fine adjustment after mounting to the transducer will be by moving the counterweight along the threads.)

Mark 1 vane
(I should probably call this the Mark 1.5 version, since the first version had a vane that I decided was too small by half, and ugly to boot.)

But I am not going to install this vane yet...  I am concerned that it may be too heavy.  To lighten it, I could make the vane out of lighter-gage brass - that would allow me to use a smaller counterweight.  Or I could make the vane bigger and mount it closer to the PVC cap - that would also mean that the counterweight could be smaller.

But before I try either of these, I am going to try my hand at making the vane assembly entirely out of aluminum.

Next weekend.

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