Batwings (stabilizers)

[Tad Roberts]

Nordhavn suggest that the additional weight of a tender up high slows the roll.
A mate with a 20 ft tender with a 115hp on his 65 after says its stiffer.
A sailing yacht , sails down, that loses a mast rolls faster/more than one with a mast.

Think metronome, move weight low it beats fast, move weight high it slows down.
It is a balance, go to high and it falls over and stays there.

Even very experienced people have a hard time separating stability and motion. One keeps you safe, the other keeps you comfortable.

Nordhavn is advocating reducing stability by raising the center of gravity of the entire vessel. Making the boat less safe, by a small amount, but more comfortable to be aboard.

The sailboat that looses it's mast has become safer (much harder to capsize) but much less comfortable to be aboard.

 

[Simi 60]

Bat wings roll up to post 55.

 

[BruceK]

Those are definitely bilge keels, not bat wings.

Apologies to bats everywhere. I liked the registration letters on the bow too.

 

[FF]

"Nordhavn is advocating reducing stability by raising the center of gravity of the entire vessel. Making the boat less safe, by a small amount, but more comfortable to be aboard."

The Schooners working the banks would hoist a heavy anchor up a mast to ease the roll speed.

 

[cardude01]

When I added the mast to my boat I was amazed at how much more gentle the roll was than before, even with no sails up. Before it was very snappy and quick, but as I headed out for the initial test cruise I got waked and was pleasantly surprised.

 

[bogranjac1]

Nice boat,
Huon pine is one of the best timbers for boat building.

It just needs a rudder.

Yes -they are bilge keels; or rolling chocks.

Bat wings aren't as long and protrude outwards (athwartship) more.

Please !!!
those are "ROLLING CHOCKS"
bilge keels protrude from the bottom of the hull commonly called the bilge ie where the bilge water collects.

 

[BruceK]

Think I`ll stick with "long thin panels sticking out from the side of the hull".

 

[North Baltic sea]

Imagine what these would be like, and don't forget they are deployed when be

Hi, it is liles same ideas whit Cruise ships wing stabilizators exsaples allure of seas. This wing can be folded inside Hull, it is great when not in use.

NBs

 

[Wxx3]

Well, one year and 68 posts later and I'm still waiting for someone to give some before and after data on these things, whatever we call them. So I become a bit skeptical of the claims. Think of a hundred people bragging about going to Las Vegas, but only about 2 talk about their results after the fact.

Larry on hobo and Cardude are the only people to provide some before and after data.
Like Larry, i also run with the poles out, as much for convenience of deploying the birds, as anything else.
Though that's what caused the Dutch CG to chase me for two days.

I've deployed my birds maybe 500? times in the last 4 years and each and every time, I record speed and roll, before and after.

 

[cardude01]

Why did they chase you for two days??

 

[MurrayM]

I've decided against batwings and am now leaning towards rolling chocks. We invariably seek out tight, twisty, thin watered passages which can have kelp. Batwings would probably get hung up while rolling chocks should offer less resistance and slide on through.

Everything is a compromise...

 

[cardude01]

What if you extended your mast (and strengthened it) and added a small main and a roller furling jib? That would help with the roll, not catch the kelp, add some get home capability, provide some shade (probably don’t need that), and give you a small boost when underway.

 

[Sealife]

All of the things being discussed here seem to affect roll period. I think that one of the biggest advantages, is to be able to change that period to match conditions. I’ve been in situations where no birds where more comfortable than both. No matter the roll period, if it syncs with the seas, it will become uncomfortable. I like a slower roll (longer period) for comfort, but only to an extent. When the angle becomes to severe, I would tolerate a quicker roll.

Just some uneducated opinions from a few thousand miles at sea....

 

[MurrayM]

What if you extended your mast (and strengthened it) and added a small main and a roller furling jib? That would help with the roll, not catch the kelp, add some get home capability, provide some shade (probably don’t need that), and give you a small boost when underway.

Sheepishly, I cast my eyes downward and mumble softly, "Boat came with mast compression that's been temporarily dealt with, until it can be fixed properly".

Comment about not needing shade was mean

 

[cardude01]

[emoji23]

 

[MurrayM]

[emoji23]

Sad, isn't it? Mast compression on a trawler

 

[cardude01]

Sad, isn't it? Mast compression on a trawler

No, I get it. Im sure most of the trawler masts were not set up for very big loads, and it’s probably a pain to get them set up for that. I’m just really pleased with my mast and sail rig for reducing roll,as well as the other benefits, and would like to wish that success on others.

 

[Simi 60]

Here's a couple of cleaner bat wing installations. These are big and heavy, 5/8" or 3/4" steel plate so well over 1000 pounds of additional ballast down low. They are not going to reduce stability.

These show the shortest possible support leg, which minimises drag compared with the type (On Poplar III) where the leg carries up above waterline.

Resurrecting this as today, I actually got to see batwings in action (not the ones Tad shows) and to say I was impressed is an understatement

And, I am assuming, the above ones are strong enough to allow the vessel to partially dry out on a suitable beach or bank so for me, that would be two jobs the one item does and worth investigating further

Add: the ones I saw working were these type.
Great on a steely but a bid vulnerable on timber me thinks
At least the Tad version is mainly keel attached

 

[DDW]

The ones you saw are retractable. When you say "saw in action"do you mean deployed in a seaway and doing a good job? or just in the yard? There is a research paper published in the Canadian Maritimes where this kind of stabilizer is apparently popular.

 

[Simi 60]

The ones I saw in operation today we're the same as in the bottom pic and we saw them in action today coming around a headland that we'd rolled around an hour earlier and into an anchorage that has us rolling somewhat now, but not as bad as the sailing yachts

The guy with the batwings is rock steady and steel.

But on a timber boats attached to hull planking they would freak me out a bit (lot) due to leverage over a short area of planking.

The keel attached variant appears to be a better and stronger attachment point and would be considerably simpler construction therefore affordable and, as it can assist with drying out as well would get a tick of approval from the financier.

 

[Simi 60]

Another article here about them.

https://www.sail-world.com/news/230372/AMSA-Safety-Alert-Fixed-(passive)-fin-stabilisers

Of further interest is the link they have to a study of various types entitled
Recent developments in roll stabilisation of fishing vessels, a study by the University of New South Wales

 

[OldDan1943]

Crab pot collector?
Fish net collector?
Wooden or fiber glass, attached to the keel??

 

[DDW]

The passive fins operate on the same principle as a centerboard. i keep wondering if a deep centerboard is all that is needed. Many trawlers have a keel with dead space in it so it would take no room out of the boat. You'd have to remember to raise it in shallow water, but it could be designed to kick up or break off in the event of collision - this is well worn engineering in sailboats.

 

[DDW]

You might also want to check the paper from Quebec, by Francis Coloumbe et. al. They compared two sister ships, one with bat wings and one with paravanes.

 

[Simi 60]

You might also want to check the paper from Quebec, by Francis Coloumbe et. al. They compared two sister ships, one with bat wings and one with paravanes.

Thanks, downloaded and read and definately turns me off of paravane types

Unfortunately it was a comparison between fold up batwings, not the fixed variant which, I imagine won't be as effective as the fold up ones but I would think more effective than rolling chocks.

 

[Jeff F]

The passive fins operate on the same principle as a centerboard. i keep wondering if a deep centerboard is all that is needed. Many trawlers have a keel with dead space in it so it would take no room out of the boat. You'd have to remember to raise it in shallow water, but it could be designed to kick up or break off in the event of collision - this is well worn engineering in sailboats.

I've wondered about that as well. Are these wing foils fitted to try for zero lift? Or are they meant to provide consistent positive or negative lift when underway? What's the optimum angle of attack to the water flow?

Paravanes are angled down to provide constant negative lift, essentially pulling down on both sides all the time. That seems to me to be part of what makes them effective, but that's an armchair POV.

 

[Simi 60]

A timber trawler with hinged batwings
It can be done
Supporting cable running to the bow on this one.

 

[Jeff F]

I've popped in to a couple of fishing ports on the Gaspe and the batwings are ubiquitous here. To answer my earlier question, it looks to me as though they have a neutral orientation in the water.

 

[Jeff F]

Here's another view.

 

[kapnd]

Paravanes are angled down to provide constant negative lift, essentially pulling down on both sides all the time. That seems to me to be part of what makes them effective, but that's an armchair POV.

If the paravanes pull downward on both sides, it is loading the boat to slow the rocking, just as would adding ballast.
Seems that the paravane on the descending side is just enhancing the roll?
I’d like to add ballast low in my boats keel, but it’s sealed, and I presume already weighted.
I’m trying to visualize adding a lead bulb to the keel.