Although the name "Flopper-Stopper" has seem to have acquired a universal meaning like "Xerox" it is a brand name although I don't know if they are still being manufactured. They are the least effective of all the devices that I have witnessed.
I agree with Steve. The Magma that WestMarine sells is a design originally called "Sea-Cure". In my opinion it works the best for the least square footage of stowage space because it folds up like a book, which is how it works anyway.
If the device is deployed to seaward
it is the most effective although it will work on the other side. It is not necessary to deploy two, port and starboard although this might not seem obvious. If the boat's rotational acceleration is limited by the anti-roll device in only one direction then the motion may be unbelievably most tolerable.
What Wheels points out is true when there is only one set of wave motion, in general I've found that, although it may not be noticeably visible, there are other sets of wave motion that bridling to the rode
will not solve. In addition, with tidal and wind
changes the boat can swing around with the anti-roll device still keeping the motion tolerable.
I have used these for decades (similar to the one sold by WM) and even made my own. One visiting couple aboard my boat who had not been acclimated complained of feeling quite queasy at anchor. After I deployed the anti-roll device they immediately felt fine.
On a sailboat I prefer to triangulate a downwind pole, attached to the mast
and deployed as close to beam-on as possible, by using a spare halyard
to the end of the pole and a fore and aft guy from a bow cleat to the end of the pole and back to an aft cleat. Adjust the halyard
so that the pole nearly bisects the angle made by the halyard and the downline attached to the anti-roll device. Make the downline sufficiently long so as to miss the keel
when a current
might carry the device towards the boat or when the boat swings (sailing at anchor) or veers towards where the device hangs in the water
. Make the downwind pole length adjustment (if you have an adjustable pole) such that the device hangs as far as possible from the side of the boat for maximum leverage against rolling.
I have a solid long boathook that will just reach the downline for retreival otherwise you have to attach a nuisance retreival line like the one shown in the photo
that Steve's link shows. If you use shackles to attach the device make SURE that they are safety
wired else you risk losing it as I did one time. In only 20 feet of clear water I dove around the boat for a long time and never found it!