Will a bilge keel improve rolling at sea?

Neat stuff. Thanks for the info.

active + passive = good combo

Quantum also has active trimtabs www.quantumhydraulic.com. Click on Stabilizers, then on Archer and Arrow. They are a.o. on the "World is not enough" from Millenium and on many others and are said to be effective.

Interceptors do the same example www.humphree.com. Instead of a trimtab, it's a blade that creates pressure on the hull bottom. Many of the fast italian and french boats have this system.

-> Bill
As to passive and active working against each other: increased passive stabilization will always be beneficial. Any hull has it's own passive roll damping, but bilge keels jsut add to that. A hard chine hull has more roll passive roll damping than a round bilge. In a sailing boat, it's the keel and rudders that provide a lot of roll damping.

Benetti is now working on a system which one could call "retractable bilge keels". When the vessel is at anchor, huge panels hinge out of the hull and provide passive roll damping. When the vessel is sailing, they are hinged back in for less resistance.
They are planning to make this system active in the future (comparable with active fins).


_____________________________________________
Bruno
www.innomare.com
Naval Architect - Owner's Representative - Marine Surveyor

wow

This thread is great, one of the most interesting yet. Thanks AMG.

I often wondered about the trim tab idea also.

My thoughts were that the planning hull would have to be moving faster for them to be affective, and in many conditions that you would need them on a planing hull you wouldn't be going at planning speed. Perhaps if you had super large tabs to counter act the loss in forward motion and thus amount of water travelling over the tabs????

Chris,

you're right, they become more effective as you go faster.

Trimtabs are more effective at lower speeds than interceptors (but they are also more complicated and expensive).
The lower the speed at which you want them to be effective, the bigger their size should be. But you're limited by the length of straight edge you have on the bottom of your transom (their width is more important than length).
The advantage of the interceptor is that it doesn't have to be straight.

________________________
Bruno
www.innomare.com

This is a system developed by Kelly Archer, hence the product name "Archer". Because the foil is mounted as an extension to a conventional-style trim tab, it will not work for Chris, assuming his ride is a true displacement hull.

Again, this system is not intended for full displacement apps. The plates are intended to mount vertically on a transom. On a side note… I really don’t like this concept. There’s something fundamentally wrong about it!

I agree Carl, still I have put them on a boat where they work really well!

But on our boats with stepped hulls they doesn´t work at all since there is too little waterflow. They doesn´t give the support of real casted offshore tabs either, so for speedfreaks I think the traditional trimtabs are better.

Carl,

you're right. We were all led off-topic by Billy1119. For a displacement ship trimtabs or interceptors don't make sense.

There you have to choose between fins, magnus-effect rotors, passive or active anti-rolling tanks, gyros, flopper stoppers, rudder stabilization and probably a few others that I am forgetting.

Oh yeah, some fishing boats have a small triangular sail on the aft deck just for roll stabilization.

Cheers,

________________
Bruno
www.innomare.com

There was a stabilizer system with a weight sliding sideways on rails. Maybe from KoopNautic, and I have seen it on a Moonen 72 where it was on the forward bulkhead of the engine room.

It was also working at anchor, but created some noise and it was scary to be in the engine room when it was moving forth and back...

Uh, yeah, sorry about that. My curiosity got the best of me.

Seems like that would have to be quite a weight. How big (heavy) are we talking about? Seems a little archaic, but hey, if it's effective...

hmm

surely it would be more advantageous for the sliding weight to be higher up on the vessel rather than down in the engine room??? Maybe it was there because of the noise and cosmetics?

It was high on brackets and this rather small yacht (72´) only has one deck above so it was probably in the ideal position. I tried to find some info on the weight today without success, but my guess is around 600-800 kg...

So, when you first described this I was thinking about a big bar with the weight just freely moving back and forth as needed. I thought about it again and that seems a little out of control... So, how was it controlled if it was? A gyro determining which way a cable should pull the weight and how far and fast?

Yes Bill, this is about the right description, can´t remember if it was a chain or cables, maybe both. So it was moving in advance of the movements of the yacht. Similar to fin stabilizers which are also moving in advance to keep the boat from swinging too much. The stabilizers (or the gyro control box) can only predict the next wave to behave as the previous and as the sea is never regular, they get out of rythm once in a while...

There are also Fram anti roll tanks which can be passive or active, the passive relies on a tuned length tube and valve arrangement, something to do with the time lag of the mass of water in the tanks and active which has a huge pump. I believe this system was installed on Eco

Enclosing active roll-fin stabilizers

The point of protecting active fins is a good one. However, ensure the protection you are installing does not interfere with the flow of water around the active fin. The fins rely on smooth water flow, just as a sail relies on undisturbed air flow.

There are new active and passive stabilizer types which mount to the transom. Since they do not protrude below the propellers and rudders they won't ground. From the transom roll pitch and yaw can be controlled under way and at anchor. Additionally, since they are located aft of the propellers they don't create disturbed water and propeller cavitation which induce hull vibration.

Smaller yachts should not require bilge keels if using the transom mounted system.

While it's true that there are now integrated stabilization systems available that control pitch, roll and yaw effectively, and several zero-speed roll control solutions...I can't quite fathom what kind of transom effectors you are referring to. Any links or other info on what they look like?

It´s been discussed earlier in this thread. Here is one supplier;
http://www.quantumhydraulic.com/ridecontrol.html

Quite familiar with those..I probably should have been more specific in stating that I was curious about the 'yaw control' part of the solutions alluded to above. The winged-tabs that Quantum builds are sometimes 'slaved', in the controller, to the vessel steering (rudder position) to eliminate yaw-roll coupling in some cases, but are not used for yaw control directly.

Transom Mounted Stabilizers

There are many ways to control all boat motion from the transom. Most are based on classic hydrofoil technology. Aircraft tail section and aileron techniques are also utilized.

The strategy is to use the force of lift generated from NACA shaped t-foils, to actively stop roll and passively dampen pitch and yaw. The effectiveness in a following sea is extraordinary, with transom mounting.

At anchor, the active t-foils attenuate roll motion and passively reduce pitch motion. This prevents the yacht from synchronizing with wave amplitude and period. This reduces roll acceleration and shortens the length of time the boat is effected by each wave cycle.

The mere fact that the hydrofoils are an added appendage under water increases drag at anchor and dampens roll, like bilge keels and flopper stoppers.