Anti-Rolling Gyro or Stabilization Fins

Just came across another thread we had on gyros...

http://www.yachtforums.com/forums/technical-discussion/12067-gyro-stabilizer.html

Gyro

Fins are defiantly better than the Sea Keeper system on the boat I was able to directly compare. I would say the gyros were less than 50% as effective as the fins and the gyros dampen the roll but do not try to seek level so if you have a strong cross wind the fins will put you level but the gyros will let you list. We are outfitting a boat with both right now so you can use the fins running and have a gyro for anchoring out.

Probaply a stupid question but why is the gyro not installed where the rolling motion is the most? Like on the flying bridge.
I am not an engineer and can't do the math but something tells me that its something with force and moment.

Gryos

Yep; I believe the phrase "polar moment of inertia" applies here, but don't ask me how.

If money were no object, it would seem that stabilizer fins and gyros would be the way to go. Presumably you'd have to heavy-up the generator(s) and the wiring to handle the extra load, so that's even more expense. Still.......

just happened on this from a PUP forum, and thought it might have some interest in these discussions


We had looked into these units when Swan Song was earlier in the stage of re-construction. At the time, according to the factory man in Japan, we'd need two of the mid-sized units to keep Swan Song from rolling less than 25 degree each side. If a sea state was at the level that we were rolling this much the power required to keep them both spinning was just over 8 KW. This all according to them. In a really nasty sea state they would need to be turned off as if they hit the stops often and with too much force they might self destruct. Suffering and surviving a knockdown wasn't in their vocabulary! All in all we opted not to go in that direction as the predictability of sea state isn't within our ability in making a passage.

As most of you know we went the route that few have taken and for the life of me I don't know why. An Anti-roll tank, ART, is our only roll reducing system on Swan Song. A totally passive device with no maintenance to date, 5 years, and only one moving part, water.

I wish I could say exactly what the numbers are for roll reduction but I can't. What I can say is that in 15,000 odd nm we have never rolled more than 30 degree and perhaps on 20-25. This includes a tough patch coming into Hawaii last year in waves that were occasionally in the 30' range. We can sit with no way on in 8-10 ft. seas with very little movement. So little that you can work on things and not be chasing tools all over the place. This is a very comforting fact especially when you have to shut down the engine for daily checks at sea.

For some reason Naval Architects hate them. They are afraid that they will somehow encourage a capsize or something similar. We have found all of this is bunk. Swan Song is stiff and has a high righting moment but it is round bilged and likes to roll and once started would go on for 12-15 rolls as a minimum. We tested all of this with full inclination tests, etc. Our boat parameters were fed into the computers that Dr Bass up in Newfoundland runs with his software and came up with the design tuned to our boat. $10,000 later it was constructed and put in place on top of Swan Song's Pilothouse. 1500 lbs. of water over our heads ;-)

Everyone who has ever been aboard either on the hook or underway is astounded by how Swan Song behaves in the water. At first they are puzzled and then as they watch other boats nearby whether they are sailboats with the masts waving in the sky or power boats showing lots of bottom paint they realized that Swan Song doesn't hear the music that the other boats are dancing to. As Seahorse John (now departed) once said in Bequia after an evening on board with the ferryboats passing 50' away without spilling the wine, "I thought you must be aground as you aren't rolling like the others". Then as he watched us round the point heading north out of the harbor the next day waiting for the first African tradewind swell to pin us down Swan Song just went on her merry way. "**** I got to get that system".

Bob Phillips, Another Asylum, has the same system done by Dr Bass. He is the one that sold me on it. Check with Bob as I think he'll compliment just about everything I've said.

I can't compare if paravanes would be as good but I don't think so especially at slow speeds, stopped or in shallow water plus they do require effort. Active fins are nothing but trouble long term and because of our size, propensity to roll, and slow speed the size of a system for Swan Song is large and in the order of $75K with all the attendant maintenance over the years. We would already be due for an overhaul. So for us the option was the paravanes or ART. Glad we made the choice we did and have never looked back.

Also as to significant wave height measurement, significant wave height is the average of the highest 1/3 of the wave. The actual wave height can be as much as 3 times that on occasion and from my experience usually is. Our height of eye is 12' off the water sitting in the pilothouse and beam waves up to this height aren't comfortable but offer no problem on the beam. Even an occasional crest coming aboard just tosses you sideways. Bigger waves that this and we are either taking them further forward or further aft. Dead down we are fine even in that 30' stuff near Hawaii. 20-30 degrees off our stern is our weak point. We get both the pitch and a roll so the corkscrew motion gets uncomfortable pretty quickly

Dave & Nancy
Swan Song
Roughwater 58

When I first seen these gryos, My first thought is why spin a mass of steel around for stability? I would design a system that uses the weight of fuel ~7# per gallon,spin that in a centerfuge(using helical screens and coalesing medium and you could get the benifits of fuel polishing,(you would have to have a steady flow rate through the centerfuge so not breakdown the fuel) . gryoscopic stablization and fuel polshing/water seperation all in one unit.

Roll tanks (called Flume tanks) have their following in Europe. I recently attended the launch of one of a series of ro-ro ferries for Med service that use flume tanks for roll stabilization. On a smaller scale, the old 24.4m class of the Norwegian NSSR rescue cutters relied entirely on a central (diesel) flume tank for roll stabilization.

I've been involved in stabilizers and have been looking into gyro based systems and zero speed stabs as the owner wanted a zero speed system to replace the current underway system. There are significant differences between both systems. Fins typically perform well when underway due to the waterspeed that creates lift. The higher the speed the bigger the lifting force. When on anchor there is no water speed and the fins generate no lift at all. The "artificial" solution is moving the fins actively while anchored. It is easy to understand that the roll reduction is not comparable at all with the roll reduction achieved underway. If one looks at the geometry of zero speed fins one notices that the fins are less high but longer called lower aspect ratio. This is to create more momentum when the fins are slewing around. Normal underway fins are higher and perform much better than the lower zero speed fins. That is why zero speed fins always have a bigger area! They are less efficient and cause more drag.

The gyro's are indefinitely better when on anchor. To get similar performance with fins one would have to fit fins with a huge area or even fit four fins. So where is the catch? Are gyro's the solution for modern yachts?
There are a few aspects to be considered such as yacht configuration and on mission profile. For fast hulls with a low mission profile I think that gyro's are the best option. You don't want big fins sticking outside on fast hulls.
For displacement hulls both options could be o.k. Mind you contrary to fins, the performance of the gyro based systems goes down when the hull speed increases.

In my view nothing can beat fins when underway and for zero speed gyro's seem to be the best choice instead of big fins that need to be slewed around. Since we have underway fins I suggested gyro's as zero speed option so we would have both systems onboard.

Roll one for me!

If the boat doesn't go anywhere, the gyros work well. But then again, why would anyone choose an anchorage where one would need stabilizers?

Not sure wat you mean by your first statement.

As to your second, there are many reasons why you might end up in a less than ideal, calm, quiet anchorage. Not to mention that some quests are much less tolerant than others about the amount and type of motion a boat my have at anchor.

Anti-Rolling Devices

I am following this thread with interest and I must tell You, I am glad to be a Blow Boater. We do not need all this complicated, trouble prown, expensive and noisy stuff. When under sail, this piece(s) of cloth on the mast not only propell(s) you, but also stabilizes your rolling movement and on the opposite side is a nice deep and heavy keel that also helps a lot. When I grew up as a boy, on my fathers big Yawl we used paravans when on anker. They where very effective. Just a little joke from one of those "disriminated" blow boaters.

But I would like to add a few educational points from my big ship point of view.

Also living in the commercial shipping world, I have piloted both full displacement and planning boats both with fin stabilisation and Gyros. Gyros are quiete effective both when moored and under way. Besides their high power consumption and very long spool up and down time, they require a lot of electrical power (AC), maintenance and propper care. This heavy piece of metal spinning at very high RPM places a lot of stress on the bearings and gimbals when encountering shocks from waves and fast manouvering. Our navy made tests on fast patrol boats with gyros in order to provide a more stable weapon platform. The Gyros did not last very long and never went into service. But I stil believe, they are the better choice for the stabilization of a planning pleasure boat up to 100 ton of displacement than fins. You would not go high speed on your car with activated parking brake either. Installation of multiple Gyros takes a lot of space, electrical power and money. But there is a system on the market called stabilizing rudder, were the 2 rudder blades are slightly tilted from the vertical and used as stabilizing fins on higher speed. Also a little trick that is used by the navy on their new frigates.

The key to fin stabilisation is their design, positioning and most of all the computer control. The resistence of an airfoil is composed of the head or frontal resistance (thickness and wingspan of the airfoil), the profile resistance (type of profile, speed and viscosity of the medium plus smoothness of the skin) and very important the induced drag which is directly dependend on the aspect ratio (the relation of wing span and profile depth) of the airfoil. Lower aspect ratio means higher induced drag. The last point is the interference drag. He is produced at the joinging of the wing (fin) and the hull. As the first two kind of drag are the trade in of an airfoil and must be lived with, the induced drag can be partially compensated for by endplates on the stabilizers (like the winglets on modern jets). Thats why the low aspect ratio zero speed stabs have or should have endplates. The next problem on fins is its downward angle away from the horizontal. As the fin should not extend the limits of the hull (damage) and should not be lower than the keel, stabilizing fins are pointed downwards and have pretty low wingspan. But an airfoil only produces lift acording to its projected wingspan. If a fin is pointed down in an angle of 45 or 60 degree it loses a lot of lift and has to compensate that by more deflection and/or faster deflection rate. This will cause the airfoil to stall and the flow behind the airfoil will be turbulent and the fin will act more as a speed brake than a stabilizer.

My solution for a full displacement boat up to 100 or 150 feet would be a well designed fin with laminar flow airfoil (that means the thickest point of the airfoil is much more to the rear of the fin) highest possible ascpect ratio and endplates but combined with strakes on the lower part of th hull.

On larger ships we are in a much better position. Rolling tanks are almost standard on merchant ships, as they are cheap and maintenance free. But the the biggest advantage on ship size is, we can use retractable fins with very high aspect ratio and mounted almost horizontal (app. max. 30 degree). The zero speed versions have moving trailing edge flaps of the flettner type. We can use 4 of them and with help of modern digital 2 or 3 axis controls systems, they reduce both roll and pitch and by including the ships rudder into the cycle also yaw to a certain extend. They come in differnt sizes and could be used on yachts from app. 200 ft upwards. Oceanco Yacht Nirvana for example uses them.

Example of retractable zero speed fins from Blohm und Voss Industries

other way

Another way are Voith-Schneider props (for new builds).

Voith | Voith Schneider Propeller

Just wondering if this type of stabilizing a boat is a rehash of old technology.

Boat stabilizes with the help of internal waves. [VIDEO]

Only have cruised throughout the Bahamas professionally for 28 years. And yes, while the can be rolly anchorages in the Bahamas (Great Inagua and Betsy Bay come to mind) I do my best to avoid them.

Well that pretty much negates the need for stabilizers. Simply avoid waves! Do you have something constructive to add?