Tubular radar reflector flutter

[ref_123]

Hello people,

once again asking for a collective wisdom. I have two tubular Plastimo radar reflectors installed on inner shrouds between the first and second spreaders. They have been there for a while, with no apparent issues. Except yesterday, when the wind came with just right strength (a lot) and from a just right direction. And oh my, they started to shake like crazy 2-3 times a second with every gust! And the whole boat was joining the dance.

Now, I know enough about aerodynamics to figure out that I have seen a live show of the Karman vortex effect. But - I never saw or heard anything like that about those reflectors! Am I just lucky? Or it's a known effect with those tubular reflectors that people do not talk about?

If you have ever seen or heard about it, please voice your opinion! Do I need to change they way they are mounted? Or put that helical thingy on top of them that saves the larger structures from the ill consequences of this dirty trick of turbulent air flows? A piece of rope wrapped around the tube should serve the purpose, or so it seems...

Thanks,
Stan

 

[footrope]

You may be unique, but not in this way

I have one of those reflectors about halfway between between the left spreaders on the main shroud. Once in a while it does something similar to what you described. The action is annoying, for sure, but shouldn't be dangerous if you don't let it go on for too many years. The action, over many occurrences, could prematurely wear your spreader tips however. I'd say move them downward, closer to the lower shroud and see what happens. That's my plan, next time I climb the mast. That will change the weight distribution on the wire segment and the forces will be acting against a slightly stiffer section of the wire. Or something like that.

I called it flutter too, when it happened to me. I'll have to look up that Karman vortex thing.