twin back stays

[plankton]

My boat has two separate back stays..the port side has a turn buckle type screw at the deck termination as i normally see on rigging..
But then after +/- 2m this port stay connects to another wire.
This wire continues to the top of the mast passing through the centre of two black cylinder gizmo's along the way.
These cylinder gizmo's +/- 10 cm long and +/- 2cm in diameter...are arranged one just above the connection and one higher up close to where the stay reaches the top of the mast...
They appear to have rounded silver ends from which the wire emerges and they look adjustable
The starboard stay just runs down uninterrupted to terminate on a normal turn buckle at the deck.
Could someone please explain the function of the two black cylinder gizmo's? and any ideas why i would have this twin back stay arrangement?
Its a fairly common boat, others i have seen have one back stay, splitting into two as it nears the stern connection.

 

[machurley22]

They sound like insulators to allow the section of backstay between them to be used as an aerial.

 

[Norman_E]

I agree. SSB radio usually uses an insulated back-stay as the aerial

 

[plankton]

Can of worms..just searched under insulators and found an article which seems to make sense “WHY DOUBLE BACKSTAYS ARE EVIL!!” http://www.briontoss.com/education/archive/miscapr99.htm
wonder if any rigging people can advise further here ?

 

[john_morris_uk]

I also agree - almost certainly insulators to make your backstay an antenna for SSB use. I'm in the market for a pair if you don't need them next time you replace your backstay, but it depends what size your rigging is.

 

[Gandolfo]

Insulated back stay isn't just for SSB. You'll get brilliant reception of Radio 4 long wave for a considerable distance

 

[Salty John]

I agree, sounds like insulators.
Brion Toss is clearly not a fan of twin backstays but he probably overstates the case against them for effect. I agree with him that the use of one of a pair of backstays as an antenna is a compromise because of interference from the other backstay.
I assume you have an outboard rudder or some other reason why the backstay can't terminate at the centre of the transom. Personally, I wouldn't lose any sleep over the present set-up but changing to a split backstay wouldn't be very complicated.

 

[plankton]

Having now seen many pics on the internet (searching on SSB insulators) mine are not an exact match for any i have seen but very similair to all..i am convinced you are all correct..I will see if I can find a way to make use of this new found aerial!!
The evil double backstay article is a tad worrying i will ask a rigger to advise if age of insulators etc is an issue with my setup and pick the most secure route. Thank you all for the clarification.

 

[MM5AHO]

I just replaced the backstay (not a double one) and inserted two of the black thingies (insulators) for HF radio.

I'm hoping that its not limited to SSB though, and that it might also work on FM, AM, Data, etc.

They are not cheap!