I've used wind vanes on passages and agree that they are very good
things. I've even considered putting one on my catamaran which has
carried me many thousands of off shore miles. However, I believe that
the costs associated with vanes are too high compared to the benefits
on my boat. Each case will be different, but here is my thinking on
this for my boat:

I. Benefits:
1) wind/water powered, works even if engine and electrical fail.
2) simple can be fixed in remote locals.
3) power savings allow for greater use of electronic nav aids like
RADAR.
4) silent.
5) amusing.
6) looks salty.

II. Costs:
1) very expensive compared to electronic self steering unless home
built.
2) Adds a lot of weight to the end of the boat reducing available
payload, increasing ptiching moment and increasing drag. Speed and
seakeeping costs are larger on total and percantage basis as boats get
lighter and faster.
3) Add wind and water drag. Drag increases greatly as boat velocity
increases so fast boats pay more than slow ones here, too.
4) Does not function in calms.
5) Functions poorly or even dangerously when boat speed approaches
wind speed. Again, a problem only for fast boats.
6) Exposed to elements, part failures, eg oars and vanes, common.
Fast boats will put more strain on the gear and should expect greater
failure rates.
7) Increased dock fees based on LOA.
8) Complicates davit arrangements
9) May make boat more difficult to manuver esp. in reverse.
10) Setting and retrieving oar or rudder can be difficult.
11) Does not steer a compass course, makes DR much more diffiuclt.
12) Look industrial.

-- Tom.