A flopper stopper you can make yourself
There are few cruising experiences less delightful than being aboard a rolling boat in a windless anchorage. Given a bit of a breeze, boats will tend to lie heading into it. The same with any tidal stream. But without benefit of such disciplining influences, most boats prefer to lie beam on to any swell, however slight, that might be surging in from some meteorological disturbance, possibly hundreds of miles away. Beam on and roll hideously, that is.
The solution to this torment is to carry a ‘flopper stopper’ – not an object of personal underwear, I hasten to add, but a device that will reduce an anchored boat’s roll. There are various proprietary ones on the market but it’s very easy to make one yourself.
The photograph (left) shows the one we carry on Shindig. It consists of an equilateral triangular plate with the corners rounded off. The 10mm thick plate is of GRP (FRP in the US) which I laminated myself on a sheet of melamine-faced chipboard. I chose GRP because it’s heavy and durable. I could have used steel or aluminium – or even plywood, though for the latter I would have needed to add extra weight to overcome its buoyancy. Naturally heavy materials are the better choice.
The corners of the plate are rounded off to reduce possible damage if they banged against the topsides. One corner carries a 5lb diver’s belt weight (any kind of weight would do – perhaps an old sacrificial zinc) and the plate is suspended by a three-part bridle made up of 10mm diameter polyester rope.
How it works is this:
The flopper stopper is suspended as far outboard as possible from the end of the boom or spinnaker pole (A). It should lowered as deep as is practicable, allowing for tidal variations if any. Ideally it shouldn’t touch bottom at any time. The plate starts out horizontal but, as the boat rolls towards it, the weighted corner dives…
…until the boat starts to roll the other way. At that point the plate snaps horizontal again presenting a huge amount of drag. The supressing effect on rolling is considerable and you’ll soon find the boat’s motion calms significantly.
A couple of points….
If using a spinnaker pole, make sure the uphaul is attached to the pole’s outboard end, not the more usual position halfway along. The loads are considerable and, if you ignore this advice, you might find yourself with a bent or broken pole.
Your flopper stopper should be proportioned to suit the size and displacement of your boat. Each side of the plate shown on this page was 28in (???) before rounding the corners. For our 40 footer it could have been a tad larger. The larger the plate the more effective it will be, but, of course, with size comes stowage problems. Basically, it’s your call.