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The Revolving Catamaran (rCat) is an asymmetric catamaran, incorporating the aerohydrofoil invention.
In addition, the hulls revolve around each other, to allow tacking and jibing.

Asymmetric catamaran with an Aerohydrofoil keel was used on SailRocket2. And set a new speed record of 65.45 knots.
But, SailRocket2 can sail on one tack only. And can hardly sail in rough weather.

Revolving Catamaran (rCat) has a configuration similar to SailRocket2.
In addition, Jibing and Tacking are possible.
In practice, Jibing and Tacking are easier than on a monohull.

As in SailRocket2, sail lift force is balanced by vertical foils, only. Weight is absolutely irrelevant.

rCat is safer in heavy weather than other catamarans, thanks to the flexibility of the hulls, and the absorption of momentum of any hull, by the hinges.

More details on the notes below.

First Sea Trial showing the Jibing and Tacking

This video is ONLY to show the turning of the asymmetric catamaran. Not the speed or other factors

This video is ONLY to show the turning of the asymmetric catamaran. Not the speed or other factors

Initial Drawings



Notes (Jibing-Tacking-Roll stability-Daggerboards-Heavy seas)


On the rCat  Jibing is a very smooth maneuver because sail and boom jibe externally.

Sail and boom are at the end of crossbeam, revolving safely far away from the crew.

The sail turns around downwind and remains slack during jibing. Similar to wind surf jibe

In practice, jibing is done slowly, calmly and easily. No rush at any wind state. Safely, even in heavy weather.


On this catamaran tacking is always successful regardless of initial speed.

Even if speed drops to zero, the mainhull keeps turning around its center, because there is no counter torque from the side-hull, nor from the sail drag.

Side-hull, with slack sail, are revolving freely around mainhull vertical hinge, to the new position. Without affecting the turning of mainhull.

The drag of the sail does not decelerate the linear movement of mainhull because sail drag decelerates the side-hull alone and swing it downwind until positioning on the new tack.

In practice, even at zero speed and zero wind, crossbeam can be manually turned from the mainhull. That will allow a quick positioning of side-hull on the new tack, and a quick turning of mainhull on the new heading.

In heavy weather boom and sail turn around, downwind and externally. Thus safely far from crew.

In practice, tacking with this catamaran is a surprise. It is easier than on a monohull.

 Roll stability of mainhull (for a future foiled version):

     Roll stability during turning:

When the two hulls are near tandem position stability may be compromised. So before any maneuver, both lifting foils of mainhull should be lowered into water, to maintain roll stability. Just like on AC75, but on rCat the sail can be fully released slack, enhancing more the stability of mainhull.
Prior to the maneuver both side vertical keels should be into water to maintain maneuverability
Lateral positioning of lifting foils should provide the necessary roll stability for that momentary tandem positioning of the hulls, like on AC75, etc.

Turning is better with crossbeam hinges released.

       Roll during straight sailing:

During straight high-speed sailing, side-hull will be airborne, flying at steady altitude. Altitude is controlled by sail inclination and mast rigging.

The hinge on mainhull for the upward elevation of crossbeam could be locked, during straight sailing (by oil-cylinder,  screw, etc)

Then, roll of mainhull will be very steady, controlled by altitude of side-hull, as in SailRocket2.

After locking the crossbeam elevation hinge, and stabilizing roll, only one lifting foil of mainhull will remain in the water,  for less drag.

Because of this great roll stability, mainhull can be designed narrow, suitable for wave piercing

     Interchangeable side keels (aerohydrofoil invention):

Port and Starboard interchangeable side keels are basic elements of the aerohydrofoil invention.
Each side keel is a lightweight vertical foil.

As in “aerohydrofoil invention” ,  each keel is counterbalancing sail lift, with hydrofoil lift. Without weight.

Sail size depends only on keel size and geometry. Ballast/weight is not a parameter anymore

As a result both hulls, can be designed as light as possible.

Mathematically rCat can have any size of sail, without heeling, only with comparable side-keel size.

Speed is increasing,  because sail is maximized and weight is minimized.

As weight is reduced, lifting foil size, lifting drag and frontal surfaces, are all reduced

Interchangeable vertical keels are both simultaneously immersed in the water only during maneuvering.
After Jibing or Tacking only one side keel remains in the water, the opposite of the sail.

Foil shape of each vertical keel can be asymmetric, to pull the sail effectively windwards.

For rough weather, to avoid a total takeoff, vertical side keels can have a horizontal hinge and the provisions to be kept steadily deep into the water, under the waves. 

     Offshore sailing of rCat:

To some extend rCat can be safer in heavy seas than ordinary catamarans.

Each hull can move independently, back and forth. Also, up and down.

If one hull stops by wave piercing, the hinges allow forward movement of the other hull alone, by its momentum.

Hinges help avoiding abrupt forces from one hull on the other. Time is given, and capsizing is not as probable as in ordinary rigid catamarans.

         Other footnotes and memos


Interchangeable Side Keels (Vertical Foils)


Optional revolving of lifting foils, for streamlining hull on relative wind



     Footnotes and Memos

    Boom turning:

When sail is slack during jibing or tacking, there is need for a smallish turning assistance on the boom. To switch the sail on the other side. A regular sheet rope is not enough to pull the boom.
On the rCat in video, there were two ropes per side.

   Sudden stop by a wave (of mainhull,  or of side-hull) :

Most probable to happen is if mainhull suddenly stops by a wave, because mainhull is in lower level.

In this case side-hull will keep-on forward alone, by its momentum. And revolve around mainhull safely into the wind.
Into the wind, sail gets slack, velocity drops. Side-hull will return by the wind, to its normal position. Sailing will commence again.
In heavy weather it is advisable to maintain both lifting foils of mainhull lowered into the water. To maintain stability if hulls get in tandem position unexpectedly

The less probable case is if side-hull stops by a wave;
Side-hull is normally flying safely above the waves based on sea state, at altitude regulated by mast inclination and rigging. So it is less likely to suffer a stop. Also side-hull is small and narrow. So it is safer on a wave contact.

Nevertheless, if this unwelcome situation happens (of side-hull being stopped by a wave, and left back to revolve downwind, increasing sail forces) an option is to automatically incline mast windward by presetting of front mast rigging, to increase side-hull altitude simultaneously with retreating downwind.
Other option is to release the boom and sail, by an automatic provision on the crossbeam angular position

Maxi craft sizes perhaps may become not so important for ocean sailing, as it is with rigid cats or trimarans.

    Mast hinge:

The hinge between crossbeam and mast has two free axes. One vertical axis to revolve mast/boom/sail, and one horizontal to incline mast towards crossbeam

That hinge is better positioned higher than on SailRocket2, in the middle of the sail area, to balance the twisting forces on the horizontal hinge and on crossbeam.

For oceanic sailing that hinge must be robust, with tight tolerances, like aircraft hinge. To avoid twisting oscillations, like on video

   Quick Turning:

During jibing and tacking, crossbeam can be revolved forcefully, to expedite mainhull turning and side-hull positioning.


When mooring astern the rCat needs the space of a monohull. Side-hull can be revolved, ahead or astern 



Andreas Gagas is a Sailor, and former helicopter pilot, instructor pilot, and warship captain.
His personal interests include:
Helicopter flight theory and aerobatic design challenges;
Design of  universal hydrofoil kits for several dinghies. External, detachable and low cost foil kits;
Aerohydrofoil concepts like the Torpedo Kite which is the only sailing craft capable of sailing through a gale.