BETTER Stability under power.

[FAST FRED]

Looking for a better solution to roll controll than "Flopper Stoppers" or fin stabilizers

I am wondering if a std style centerboard would produce roll controll if fitted with a tab at the after end?

If the board case had to be wider to give the board sufficent angle of attack , or located in a different fore & aft position from a sail boat , that would not be a problem.

Cheap to install, grounding no hassle , retract when plaining.

FAST FRED



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[Crag Cay]

Billions of dollars have been thrown at this problem. The military want stable gun platforms and passenger / cruise ships / ferries want to reduce the vomit volume, etc.

The force needed to counter act a roll is enormous. Fixed appendages on the hull (in any position) have proved to be less than effective, and more often just the source of drag. I think I have seen every conceivable variation tried, at least in the test tank. Gyros and all sorts are promised to be 'just around the corner'.

These huge anti-roll acting forces are either provided by the very long lever arms on flopper stoppers or the high hydrodynamics efficiency of fully active fins. Merely adding a trim tab to the back of the passive foil wouldn't give you anything like the moments required. You can try it out. Most sailboats have exactly the arrangement you advocate at the back of the boat. Try wiggling the tiller around and see how much much roll damping you can achieve.

[RANCHI OTTO]

Why not an ASD (Arrow System Design) hull shape ?

No roll at all...

[FAST FRED]

If the board were "loose" in the case it could get a far better angle of attack and should develop as much force as a specialized side fin set .

It hardly matters where on the hull the roll input is given , if the roll board were the size of the combined fins , wouldn't the results be the same?

Although the roll board boat could be run aground without the damage that could sweep the roll fins.


FAST FRED

[RANCHI OTTO]

Adding volume in the after part you shift the l.c.b. in direction to the l.c.g. that for high speed boats is very aft.
So doing you get in planing conditions in a few seconds with no overloading of the engines.

At manouvring at full speeds (until yet I've ASD up to 86 knots) the heeling angle is less that 4 deg.

All mouvements at full speed are only vertical with no roll or porpoising at all.

More volume in engine room means, for tropical conditions, more air inside with less loss of engine performances.

The dynamic long. trim is very small and the boat runs well out of water with reduced side waves. The propulsion works in a parallel fluid with very good speed results.

The first boat is running at 53 knots, and the second one at 42 knots....
Their displacements are 20 t and 11.5 t.
In the pics they seam to be very light on water...

The second is the STAR NAJA ASD, with a displ. of 11.5 t and 2 x 425 hp has reach speeds over 40 knots in tropical conditions....not bad!
Find better....

[Crag Cay]

I.m a bit confused here. What sort of application are you talking about? The ASD hull form does provide addition stability to a fast planing hull, but doesn't do much to help at displacement speeds.

A simple centreboard will damp rythmic rolling to some extent. There are reports of people having some success on slim vessels with S/L ratios around 1.5 or so. There are also loads of contrary reports as well. The consensus seems to be that passive fins on the hull have only limited success at best.

If you plan to have some method of altering the angle of attack of your centreboard, then effectively you are building a retractable stabilising fin, with all the complexity that involves. These do work and are available comercially.

But they are never mounted on the centre line. It would work like a rudder and the boats course would be all over the place.

You need to think about you axis of influence with these things. The ideal place for control surfaces that control roll are perpendicular to the topsides. This is where aeroplanes have them, and they certainly don't use vertical fins for this, ie the rudder. Unfortunately we have to lower them down the hull to get them in the water, and then a bit more to get them to stay in the water, and some times a bit more so they don't catch on the dockside. All this is reducing their efficiency. These things do induce pitch as well, but having them in equal and opposite pairs helps as does the high level of longitudinal stabilty in boats.

With very fast boats you can move then round onto the transom and have them combined with a trim tab function.

[marshmat]

If you have $400,000 to throw at the problem, there are a few gyro wheel systems starting to come on market.... huge power draw and insanely expensive, plus they're heavy, but reports so far indicate that most of them work pretty well.

[caradot]

does anyone know anything more about those gyro systems? i am in hatteras for a fishing tournament and saw a boat that apparently has a gyro installed in it. didn't get a chance to talk to anyone about it but it sure looks like it is actually a gyro.

[messabout]

For low speed operation a riding sail will help dampen roll but does not help much with pitch.

[mydauphin]

For low speed operation a riding sail will help dampen roll but does not help much with pitch.

It is crazy to discuss this generalities. Powerboats, sailboats, large boat, small boat, planning, displacement all have different systems.

In larger boats trim tanks are used. As mention a sail can be a great dampening stabilizer. Also there are systems that move trim tabs in respond to gyro.

I rather have passive systems. Flopper stoppers can be plain dangerous. Active hydaulic stabilizers are just waiting to break.

A combination of good hull design, and passive systems might be best eventhough it might not work as well as active fins.

[Guillermo]

Fred,
Just in case you haven't already read this....
http://www.kastenmarine.com/roll_attenuation.htm
Cheers.

[kengrome]

What's wrong with a sail? It not only dampens rolling motion but it also makes the boat more efficient. Sometimes simple or low-tect really is the best solution ... :)