You can hang a pennant like this from the mast, but don't use a Jackite. I have one and they are really neat but pretty delicate just like a kite. When on the beach in a camper we'd attach a bird Jackite to an old rod and reel set in a holder in the sand, get it up a couple hundred feet and let it go for the day. I may try it off the aft end of the boat on the hook. Its not for near point work. Still the concept is sound, consider a nylon pennant with moving parts hanging off it which works at anchor or mooring since it will always stream aft fluttering over the cabin (this one is sold by Overtons.com):
However, even on a mooring this last summer my cabin roof stayed bristol while the bimini was covered with bird poop something fierce. I explored spiders (they come in different sizes (4', 6' and 8') which, as said before, work well with a sandbag mount on top of the bimini. The problem is where to store the thing on the boat underway as it doesn't fold up–you sort of bunch the wires altogether but its not flat and the 6' or 8' model would have to go in the cave. If you are committed to the spider option, shop on the internet. The Daddi Long Legs 6' model ranges from $40 to $49, with the cheapest I found at Absolute Bird Control
http://absolutebirdcontrol.com/products/bird-spider as did Tampa Tug per his note above. Plan on another $30 for a base or $48 for a rail mount base.
The best option I found was the old standby 6 foot Gullsweep which costs about $40; it also comes in a 3' model. Its not cheap, but its actually nicely made and pretty durable and worth the money.
While I bought a sandbag (not cheap, around $30) I was afraid the thing would eventually put a sag in my canvas if it moved off a bimini support–the same problem exists for the spider. The bag does have attachments for tie down ropes, but now that's getting to be a hassle... Instead I bought (another $31, but also very well made) a neat rail bracket which attaches to the aft sport rack in the middle. It comes in two versions, one for rails up to 1" and the other for rails up to 1 5/8" which is overkill:
The best thing about the Gullsweep is that it folds to 3 foot long and nicely packs away on the ceiling bulkhead of an R25. When you stand at the helm and look aft and up, you'll see the ceiling is stepped with teak boards spanning the width of the cabin at two places. Its tough to describe this, and I don't have access to my boat to take a picture at the moment, so I'll borrow a TugNut's picture from his photo album to show you this excellent storage place I think few people even think of. By the way, can you guess which TugNut would have a shark gun aboard a 25' boat? The answer is below:
Instead of a shark gun, I mounted a spare (collapsed) boat hook in this nifty spot using those SS clips we all buy at West Marine to mount a boat hook in our cockpits. When not in use the folded Gullsweep fits nicely behind it. The boat hook is a Shurhold model with this attachment on it so I can grab it, attach a line and "try" to lean out the helm window to loop cleats. Thus, its appropriate to carry it inside the boat. So far I have not yet caught a cleat, but did manage to loose the attachment trying. The Shurhold pole does double duty as a brush handle and you can even mount a paddle to it (sort of a poor man's kicker engine):
I leave the mount in place on the rail. The only downside is that the sweep only covers the front half of the bimini. I'll have to wait until next summer when the boat hangs on a mooring all season to see if it sweeps enough to deter the flying rats, as we call gulls on Cape Cod. BTW, did you guess captd (Darrell) of
Mis Dee and then
Lucky Fin would carry a shark gun!
