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.
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
On the rCat Jibing is a very smooth maneuver.
Sail is at the other end of crossbeam, safely away from the crew.
The sail turns around downwind, and externally. Sail is slack during jibing.
Maneuver is done calmly and easily. No rush at any wind state. Safely, even in heavy weather.
Tacking on this catamaran, is always successful regardless of initial speed.
Even if speed drops to zero mainhull keeps turning, because there is no counter torque from the side-hull, neither from 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 as it swings downwind.
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 counter turning of mainhull on the new heading.
In heavy weather boom and sail turn around, downwind and externally. And safely far from crew.
Tacking with this catamaran is actually easier than on a monohull.
Interchangeable side keels:
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, far on the other end of crossbeam, with hydrofoil lift. Without weight.
Sail size depends only on keel size and geometry. Ballast is not a parameter anymore
As a result both hulls, can be designed as light as possible, using ultralight materials.
Theoretically rCat can have any size of sail, without heeling, only with comparable keels.
Speed will be increasing, because weight can be greatly reduced
As weight is reduced, lifting foil size, lifting drag and frontal surfaces, are all getting reduced
Interchangeable vertical keels are both simultaneously in the water only for maneuvering.
After Jibing or Tacking only one side keel will remain 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 catamarans.
Roll stability of mainhull (for a future foiled version):
Roll during turning:
When the two hulls are near tandem position stability may be compromised. So before any manuever, both lifting foils of mainhull should be lowered into water, to maintain roll stability. Also both side vertical keels should be into water to maintain maneuverability
Configuration, and lateral positioning of lifting foils should provide the necessary roll stability for that momentary tandem positioning of the hulls.
Turning is better with all 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
Boom and Sail Options
Interchangeable Side Keels (Vertical Foils)
Optional revolving of lifting foils, for streamlining hull on relative wind
Footnotes and Memos
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.
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
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.