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I33 04-02-2007 10:30 AM

Wazza Flopper Stopper?
I see these Flopper Stoppers as equipment for boats on Yachtworld. What are they?

TrueBlue 04-02-2007 10:35 AM

Here's Bruce Robert's description, from Passage Maker:


'Flopper Stoppers' is the name generally given to a device that has been successfully used by long distance powerboats to reduce rolling. The rig consists of one pole each side of the vessel that is pivoted at or near deck level. The poles are rigged with guy wires so allow them to be swung out at right angles to the vessel and parallel to the surface of the water. Twin triangular devices of about 1 sq. ft / 0.09 sq. M each are suspended by wires from the poles so that the 'fins' are sufficiently below water level to act as stabilizers. The rig generally resembles that seen on prawn or shrimp trawlers except the boards are replaced with the fins.
Apparently, they're not very commonly used on sailboats.

sailingdog 04-02-2007 10:46 AM

The ones used on sailboats are square box-like things that have flaps that allow them to move through the water easily in one direction but resist motion in the other. They're designed to help reduce the rolling of boats while at anchor or docked.

Lurch 04-02-2007 10:49 AM

roll dampeners
A pretty good description is here:
Centre for Marine Science and Technology

goose327 04-02-2007 11:08 AM

[quote=sailingdog]The ones used on sailboats are square box-like things that have flaps that allow them to move through the water easily in one direction but resist motion in the other. They're designed to help reduce the rolling of boats while at anchor or docked.[/quote]

Yup, what SD said.
Personally I don't see why anyone would use them. If I want to sleep on the hard I'll do it at home.:D

SmartCaptain 04-02-2007 11:36 AM

Hi Gil,
I've used a home-made version of the "flopper stopper" on my 38' full-keel sailboat while anchored in Key West. You'll need three or four five-gallon pails (available at the nearest "Dumpster Marine" outlet store), a 20' piece of 1/2" line, two old rubber door mats, some dive weights and a 2" hole saw.

Cut five 2" holes in the bottom of each pail, then cut a circular piece of doormat to fit in the bottom of each pail. Drill a hole through the middle of each pail so you can string them with about 8" of space between each one on the 1/2" line. Attach some sort of weight (e.g. 15 lbs of dive weights, rocks, etc) on the bottom end of the bottom bucket.

This rig is deployed over the side at the end of your whisker pole swung out abeam of your boat. As the boat rolls down, the weights pull the pails down and the doormat "valve flaps" allow water to rush in easily. As the boat rolls back up the valves flap shut and the upward pull on the pails is quite considerable. Multiply by the length of your whisker pole, and you have a pretty good "lateral sea anchor" to help reduce rolling.

IMPORTANT NOTE: Use your main halyard or other sturdy line to support the ouboard end of the whisker pole. Most topping lifts are not made for the heavy load that the pails will put on the up-stroke.

Hope this helps,


I33 04-02-2007 11:52 AM

example pix
Here is an example, but details are pretty hard to make out.

Do these things actually make landlubbers more comfortable? :D

Cruisingdad 04-02-2007 11:55 AM


I guess everyone here is pretty much correct. I will just add a bit:

A Paravane Stabilizer (also know as a flopper stopper) is in fact a device that slows the rocking from side to side on a boat. However, I find it is generally a term associated with full/semi-displaceement trawlers.

It was originally designed by the offshore shrimpers/trawling fish boats. It consists of two "poles" stretching off to either side of the boat. Long lines are lead from the poles down to what are commonly called fish (look like odd-shaped anchors). By presenting weighted "fish" that have the effect of pulling downwhen moving, the boat maintains an easy motion at sea.

Flopper stoppers are probably most effective while moving, but many people will tell you they work at anchor too. They are commonly employed on offshore trawlers and fishing boats, even today, with Nordhavn being one of the most recogninzed to use them. Here is a good example. THe fish are hanging on his transom: Boats and Yachts for Sale

Many manufaturers of offshore trawlers have moved away from flopper stoppers (paravane stabilizers) in lieu of an active stabilization (versus passive stabilization). Part of the reason for this movement is the potential for a serious/deadly effect of losing one of the fish when they are both deployed, often causing the boat to round up and broach or heel so far to one side, it partially capsizes: The use of roll damping paravane systems (paravane stabilizers) - #15/2000 - Ship Safety Bulletin - Marine Safety

Active stabilizers, like the Naiad stabilizers (- Naiad® Marine Systems) are like little fins that move up and down under the boat, keeping the boat flat in a rolling sea. However, these stabilizers only work while that boat is moving. They work well, but are prone to failure (as was reported on the Nordhavn rally from Fl to Gibraltar) and are quite expensive (around 25-35k, as I recall). Still, with the dangers and effort requires for a paravane, they may still be the best overall answer. In fact, Nordhavn has pushed away from reccomending paravane in lieu of Naiad's.

Hope that helps.

- CD

XTR 04-02-2007 12:09 PM

Shrimp boats drop them off the outriggers, that works, but you've got a really long outriggers (30ft+) hanging out there.

Valiente 04-02-2007 12:39 PM

The Pardeys use them at anchor and instructions on how to make them are found on their DVDs. They use a box-type with a flapper valve, presumably so that they can be folded flat for stowing, but the rigging method seems identical to SmartCaptain's. Needless to say, they were homemade...the Pardeys don't like to buy what they can make!

Frankly, they seemed like a pretty good idea. Some anchorages that are otherwise safe and secure can get very sloppy. Also, I suppose deploying this device could fall under "chafe gear" because a boat that isn't rolling over 40 degree arcs is less likely to chafe. I would use this plus a riding sail.

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