Flopper Stopper Stabilisers

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colinmi

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Im looking for advice about the installation of pasive stabilisers on our 11meter wooden motor boat. The boat is a semi displacement type hull which typically travels at 7 or 8 knots.

Im interested in design of the rig to make sure that the boats structure can support everything. Would most likely make up most of it myself, but would need to buy some of the specialist bits and pieces.

Activated fins are not an option as there is no space to install and cost would be excessive.

Anyone out there already done this, have a boat already fitted out with them or even a suggestion as to professionals I could contact.

Thanks Colin
 
Yep PS

Thats my understanding as well. I dont thnk it would be worth the hassle for the usual weekend cruising we do, but next year we are off for a bit of an adventure, up to 12 months on the boat, starting on the West coast and hopefully ending up in Portugal.

Im hoping a bit of stabilisation will make the longer voyage times a bit more comfortable and maybe get us out of port on days when we might previously have stayed put.
 
Thanks TW

But Im mostly interested with stability, whilst underway. That said, whats this gyro thing...... I mean I know what a gyro is, but whats it to do with stability whilst at anchor?

We do have a decent generator....About 4 kva with an ability tom start high inductive loads.

Cheers Colin
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Nick_H is this poster, and IIRC he made some flopper stoppers to stabilize the boat when anchored.
But you're actually considering paravanes to be used while cruising, right?
Not something I'd want to deal with in my boat, I must say.
Active fins are more effective, available at the push of a button, and nowadays very reliable.
But unfortunately you're dead right about higher cost.
Re. gyro stabs, you can have a look at www.seakeeper.com, but they're also rather expensive, and can take even more internal space than fin stabs.
 
Very simply the gyro reisists motion in one plane and is set up to resist rolling motion. Its a dense flywheel spun up by an electric motor.

Have a look at this they work underway and at anchor.
http://www.seakeeper.com/

There are a few makes this site shows you what they do, but I may have access to a small batch of UK made gyros that would suit smaller boats. send me an e-mail with boat details if your interested.
 
Flopper stoppers great piece of equipment.Fitted to a previous boat a 34 ft trawler yacht I made all the equipment myself tested in belfast lough with easterly f 7 beam seas with fish down 5 deg roll surperb.
with fish deployed loose about .5 knot speed
if you would like more info pm me.
 
Thanks for the link. There is a reference there to some back issues of Passage maker magazine. Ill have a go at getting hold of those.

We do have a steading sail and often use it. It does help a bit but we are looking for something a bit better.
 
Flopper Stoppers

I understand this is a reply to an old post but as I've only just found it....

I wrote a paper on passive dampers of this type for my dissertation a couple of years ago.

If you are interested I can send you a copy....

The fundamental principle is twofold the resistance of the plate damps the roll through two effects.

1) energy adsorbtion .... added resistance to roll

2) Temporary reduction in how stiff the vessel is in roll (the stiffer the vessel or the more stable... the faster the roll).

The simple rules for damper plates are

1) You must size the damper plate properly....(a bit of ply bridled on ropes an weighted eonough to sink .. you may need to weight both edges but one more than the other so the plate flips up and dives as the boat rlls towards it.... is good enough) Too small has little or no effect... too large makes the plate unstable in the flow it is trying to resist and can make the situation worse ! there is a calculation you can do for your boat but it's quite complex and involves an amount of naval architecture or if you drop me the details of the boat I can give you a broad brush guideline as to size (it's smaller than you might think!).

2) the further away from the centreline of the boat and the higher from the water line the suspension point is the better.... the distance from the centrline has a cubed force effect and the higher the suspension point has a greater effect on the fundamental stability.


The other thing to consider is roll harmonics .... every boat has a frequency at which it likes to roll ! so when the wave train frequency matches the boats natural frequency the rolling effect is amplified.

Deploying flopper stoppers on both sides of the vessel just shifts the natural roll frequency... so roll can be just as bad or even worse if the wave trian frequency in the anchorage shifts to match.


Deploying on one side has a broader range of effect as one half of the roll cycle is at a different frequency from the other giving a smoother and broader range of damping but with slightly reduced damping overall ... makes for a more comfortable night as wave frequencies shift regularly.... but if the roll is relly bad you should probably just change anchorage !


Any one interested just let me know and I'll send a copy of the paper (withoout the stats as that's a shed load of data ! but the graphs etc. included)



Regards
Tim Abram
GMRINA; Bsc.(Hons) Yacht manufacturing and surveying
 
Please can we not use this thread. Please can we put all discussion on the other thread called "flopper stoppers" - the one that nick is OP of. Thanks!
 
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