Backstay Antenna/Windvane Question - Attn Terry Hill

Terry:

You wrote:

“I read your post in the BCC group regarding the windvane. I was
wondering if you will be able to use the backstay antenna with a
windvane on the backstay? or do you have to choose one or the other?”

I believe it is possible to use the backstay as an antenna when a backstay windvane is fitted to the boat. My only concern would be signal coupling between the antenna lead that runs along the backstay from the turner to the antenna section of the backstay. The mass of the windvane and its control wheel and upper strut may affect signal quality. SSB and HAM are not my areas hence I can only question whether there would be an antenna coupling problem. Perhaps someone at the BCC forum can answer the coupling question.

The reason I have to remove the antenna isolators, is to fit the ball bearing races and their associated bearing block flanges on the backstay. The I.D. of the ball bearing race is 1".

To address your question, I envision several approached to using the backstay as an antenna and pivot point for the windvane: (In all approaches, a split plastic armature is clamped to the backstay where the control wheel and upper strut are fitted. This serves as the shaft for the 1" I.D ball bearings. Because the armature is plastic, the windvane is isolated from the backstay by the plastic armatures at both contact points on the backstay - the control wheel and upper wing support strut.):

  1. The control wheel is mounted above the lower antenna isolator and the upper strut supporting the wing is split and uses a split plastic sleeve
    bearing. This would allow mounting of the upper strut without the need for the bearing or strut to pass over the isolator,

2 The control wheel is mounted above the lower antenna isolator and the upper strut and ball bearing are mounted before the lower antenna isolator is made-up with the backstay.

  1. The control wheel is mounted below the lower antenna isolator. With this approach, the antenna lead from the turner would have to pass through the 1" O.D. split plastic armature that is clamped to the backstay and serves as a shaft for the 1" I.D. ball bearings. Again, the upper strut could use either a split sleeve bearing or a ball bearing, depending on your mounting preference.

The split plastic armature which severs as the shaft for the 1" I.D. ball bearings, is placed over the backstay and clamped onto the backstay with split stainless steel collars. I had a machine shop, line bore the plastic cylindrical armature to the diameter of IDUNA’s backstay (9/32"). After the armature was bored, the shop split the armature lengthwise into two equal halves. This type of split armature could be modified to accept an antenna cable. It would be necessary to first bore a lengthwise center hole then bore another hole off-center and parallel to the center bore for the antenna cable. The armature would have to be split lengthwise, such that the split would pass through both lengthwise holes. This configuration would permit the armature to be clamped around the backstay and clamped around the antenna lead. it may be necessary to increase the diameter of the split armature. In this case, a ball bearing with a larger I.D. is required.

I believe this arrangement would work mechanically but I do not know if there would be any coupling effects between the antenna lead cable, the backstay and the mass of the windvane assembly. Unfortunately, I can not answer that question.

When I finally mount my windvane, I plan to photographic it in detail and post the images with descriptions on a website I am building for IDUNA. I have not decided at this point if I will publish the plans and engineering calculations on the website. I have already thought of different ways to reduce the weight of the control wheel but at a cost increase. The windvane with its control wheel and strut cost about $300 in materials. Most of that cost is in the bearings and their associated flange mounting blocks. We already had the trim tab. It came with the boat, hence I did not have that additional expense above that of the boat. If I had to build the trim tab and tab supports. I would build the gudgeons from thick walled fiberglass tubing instead of using bronze castings. The rudder part of the tab is mahogany and the tab shaft is a 3/4" diameter bronze rod. I still need to fabricate a bearing support at the rudder head for the bronze shaft. My total cost estimate is $450 for the windvane and trim tab modifications. If you had to fabricate the trim tab, gudgeons, windvane, etc, I believe one can build the whole system for $750 to $1,000. Construction of this system is well within the scope of most sailors using hand tools, drill and saber saw but it is labor intensive. I do have a radial arm saw, which was used to cut the two wing spars. Although the wing spars could be cut with a saber saw, the table top or radial arm saw makes the task easier.

Fair Winds,

Rod
S/V IDUNA

P.S. I sent the above message to your personal e-mail address but it was returned twice, hence the reason for posting on the BCC discussion forum.