We have an auto-pilot (click here) which consists of a P70 control unit, SPX-30 Smartpilot Corepack and a type 2 short stroke linear drive, all made by Raytheon. This works great for short runs around the Chesapeake Bay or maybe for day hops between islands but it has two big disadvantages. It's a major power hog and it doesn't hold up in bad weather. Our plans include some long cruising between stops and we really need something that won't suck down our battery power. We're also most likely going to hit bad weather now and then with nowhere to run and hide. We're going to need an auto-pilot that won't go on strike, ever. On our trip to Bermuda we hit a storm and the auto-pilot wasn't able to keep up with the waves. It gave up when we needed it the most and I had to hand steer for 12 hours straight. Driving a car for 12 hours is tiring. Driving a boat in high winds and 15' - 20' waves for 12 hours is exhausting.
"Imagine yourself holding an oar with its blade behind a boat that travels forward. You will do fine as long as the edge of the blade is aligned with the direction of the boat. If you twist the oar, even a fraction, the water will hit the flat surface of the blade and you will be unable to keep the oar straight - it will swing to the side. A tremendous leverage is created from the blade, through the shaft, to the end of the oar where you are holding on.
A servo pendulum gear uses this great leverage to keep the yacht on course. An oar or paddle is suspended like a pendulum from the stern of the boat. As long as the yacht is on course, the oar blade trails on the center line. The airvane is the sensor that controls the servo pendulum oar. When the boat wanders off course the airvane will sense this and rotate the oar. The flow of water hitting the blade broadface causes the pendulum oar to swing to the side with great force. The pendulum is connected through lines to the wheel or tiller and the resulting movement of the yacht's rudder brings the boat back on course."
The only power it uses is the power of the wind and water. It makes no noise. It performs better as the wind increases. It doesn't complain about working the midnight shift and it doesn't drink my whiskey or smoke my cigars. Perfect! The biggest difference between the Monitor and the auto-pilot is that the Monitor holds a course as an angle to the wind and the auto-pilot holds a course according to GPS coordinates. Now you might think it's better to hold your course by GPS and this would work well for a vessel under power but we're a sailing vessel and we set our sails to the wind. Out in the ocean the wind tends to blow fairly consistently for long periods of time. You can adjust your sails for the course you want and then set the Monitor to maintain that angle to the wind. As long as you initially set your sails correctly the boat will always hold that setting no matter what the wind does. If the wind does shift you simply adjust the vane on the Monitor to bring it back to the course you want, then readjust your sails.
This past Winter we made a list of major purchases we needed to make for the boat over the next year. We have five items at the top of that list and none of them are cheap. A new Monitor wind vane costs about $4500. Every now and then you can find a used one for sale but they get grabbed up pretty quickly, usually in days of being listed. I looked around the usual places and did find some ads but they were already sold by the time I got to them. I checked EBay and found nothing. Then I tried Craigslist, which is supposed to be "local sales". I hit the Annapolis area, then Baltimore, then DC. Nothing. Then I tried coastal areas in Virginia, North Carolina, South Carolina and Georgia. Still nothing. When I finally got down to southern Florida I found what I was looking for. There was an ad just recently posted for a 30 year old Monitor that had been faithfully maintained and updated with new parts. It came with a box of spare parts and two new wind vanes for light and heavy winds. All the control lines had recently been replaced with 1/4" Dyneema. Asking price was $1500. I jumped on it, contacted the owner and made the deal. This is a large item and shipping came to $140 by FedEx.
Update 09/15/14 -
I've
finally gotten through the restoration of the Monitor wind vane. This
turned out to be a much larger project than I first imagined. When I
started in on this I pictured it as a simple cleanup with a few
replacement parts. Silly boy. The wind vane is 28 years old and
although it was well taken care of I don't think it was ever fully taken
apart and cleaned up. These older units built prior to October 1991
were made of 304 stainless steel which tends to develop surface
corrosion in harsh environments. They now make them with 316 stainless
which holds up much better. The 304 stuff is still OK but it requires
more attention. It needs to be cleaned, polished and waxed to keep it
in good condition. There's also a concern about crevice corrosion which
can occur in tight areas that don't get fresh air such as in welds or
between tight surfaces. I did find one area that had signs of crevice
corrosion but because of the location decided it wasn't going to be a
problem.The rebuild required a complete dismantling of the wind vane. Once I had it torn down I went though and cleaned and polished every square inch to remove any sign of surface corrosion. This took the most time and was the worst part of the project. I used a product called Flitz and it made the job much easier. Once I got everything polished I went back and gave it all a good coat of wax.
As
I went through the restoration I found several parts that needed
replacing. The bushing retainers for the pinion gear were cracked and
had to be ground out and new ones welded in. There were plastic shims
and bushings that simply crumbled in my hand due to age and salt water
exposure. The pulley used to adjust the angle of the wind vane on top
was made from aluminum and was completely corroded. It's replacement
part is made of Delrin and should last a lifetime.
I
think I mentioned before how amazed I was to find that Scanmar kept
records of every Monitor ever made. Most parts were still available
too. The basic design hasn't changed much since it was first introduced
back in 1975. The biggest difference I found was in the pinion gear
(part #36). Where it mounts on the shaft the older pinion gear is
shorter and uses a bushing and washers to take up the slack and
correctly align it with the ring gear. I had to replace the bushing and
had trouble finding something suitable. I ended up using a short
length of 3/4" PVC pipe used for above ground wiring. It says it's
resistant to sunlight but I'm going to keep an eye on it. Might make a
cover for it to prevent the UV rays from breaking down the plastic. A
nice chunk of bronze would be a better choice. If I wasn't so cheap I
could have replaced the pinion gear ($274) and then wouldn't need the
bushing. The pinion shaft (part #33, $38) also had to be replaced due
to wear. I also ended up buying a "Cruising Parts Kit" (#801,$60) which
provided most of the small parts I needed. One problem I ran into is
that there isn't really a manual with instructions on how to rebuild
this thing. The parts list has some very nice exploded diagrams but
that's all you get. Some parts, especially the yoke assembly, all have
to go together in a certain order. If you get it wrong the entire thing
has to be taken apart and re-done. I went through that more than a few
times. Each time you take it apart all the bearings fall out too.
Fun.So, the worst part of the wind vane project is over. Now I just have to install it. I need to make up four backing plates for the mounting brackets so for now the wind vane patiently waits in the shed.
