Review: Axcell 65' Hybrid-Air Power Catamaran

How the Axcell 65 Catamaran Hull Works​

The Axcell 65 Catamaran is a hybrid hull, combining the properties of three different hull types, each known for efficient characteristics, but until now, have never been brought together in one hull form.

1. It is one part Catamaran with the inherent stability that comes from the wide foot print of a pair of separated hulls. As with most cats, the volumetric area within the tunnel decreases towards the rear of the hull, creating a compression effect as air passes between the sponsons and is trapped beneath the tunnel and the surface of the water, thus developing an increasing amount of lift before it is expelled at the stern of the craft.

2. It is one part Hovercraft, which forces air into a chamber (or a skirt). This creates lift and reduces wetted surface, thus minimizing drag. With the Axcell 65 Cat, this ‘skirt’ is formed into each sponson. As the craft moves forward, the pressurized air follows a channel in the sponson that gradually becomes shallower, which creates compression and adds additional lift.

3. It is one part Surface Effect Vessel, which is a shallow draft hull form that forces air into a pocket with no place to escape. As air passes under the hull, it becomes compressed between the hull and the water's surface, eventually being forced to pass under the submerged section of the hull and exit at the rear. This creates an air cushion and a dramatic reduction in drag.

This detail shot of the model shows the bottom of the hull. The intricate design delivers a startling leap in sub-surface technology.

Bringing three different hull forms together is where Bruce Barsumian’s brilliance came into play, along with a healthy dose of fortitude and persistence. The Axcell 65 Cat is based on a pair of symmetrical sponsons that are V-shaped at entry, but quickly transition into a cathedral design, then give way to a recessed cavity being pressurized by hydraulically driven fans; PTO’s from the main engines that power a hydraulic pump. This in-turn powers the blowers, providing some 30,000 lbs. of lift to a boat that weighs around 60,000 lbs. The fans take approximately 6% of the power off the main engines, which are C18s.

And where is this air coming from? One of the most distinctive features of the Axcell 65 Cat is a pair of signature ‘gills’, located on each side of the boat. These intakes are both stylish and functional. Mounted above the sheerline, away from spray, they provide fuel to a pair of large, centrifugal fans. While this might sound like a lot of plumbing, it’s really no more complicated than adding a turbocharger, albeit a monster compressor!

And what is the result of all this technology? Efficiency! As power on the C-18’s come up, the centrifugal fans engage around 1350 RPM’s, pressurizing the subsurface cavities and providing lift as the boat begins to plane. The fans are automatically synched to engine RPM and the transition is surprisingly seamless. A noticeable amount of lift takes place and it is felt midship, at the center of gravity. At an economical cruise speed of 22 knots, the Axcell Cat is consuming 23 GPH per engine; respectable fuel economy for a 65’ boat weighing in at 60,000+ lbs.

This pic shows the inside of the hull...

A side-view cutaway demonstrates how this semi-military style hovercraft application applies to the craft underway. Air is fed through the Gills and into the centrifugal fans which pressurize each sponson skirt. As the hull moves forward, air is channelled aft in a cavity that becomes progressively shallower, providing additional compression (lift) before expulsion.

Top speed on our sea trial was just shy of 35 knots, which is far less than computational analysis. Theoretically, this boat should easily top 40 knots with a potential 43-45 knots, but it is still in the development stages with further testing of props, fuel mapping, etc. At the time of our sea trial, the engines had not received a software update from Caterpillar and had yet to achieve their max-rated RPM. In this offshore aft shot, a combination of pressurized sponsons that release entrapped air beyond the transom to surface piercing drives results in a diffused rooster tail...

If there is one area where the Axcell cat fails to excel, it is in ride quality over short frequency waves, such as one-foot bay chop being whipped up by high wind. There is an interaction taking place at the bow, between the sponsons, as water is displaced by the entry of each sponson and collides inside the tunnel at the same point that oncoming waves are passing underneath the hull. Refer to the oncoming, offshore running shot of the bow for a visual. The result is a fair amount of vibration being transmitted throughout the vessel, but only at a certain speed echelon. Otherwise, the ride was smooth and stable.

During our sea trial, we purposely disengaged the fans at 30 knots and promptly watched our speed drop to 22 knots, at the same power setting. Guess what else dropped? The entire boat! A very discernable 8-10 inches, maybe more. When we engaged the fans again, the boat elevated itself up out of the water and we resumed our original speed of 30 knots. Gotta tell you, I’ve been aboard a variety of hulls designed to develop maximum lift, but never anything like this! At an economical cruise of 18 knots, the Axcell 65 produces a very low wake signature, as seen in this picture...

Powering up, there is no ‘hump’ coming on plane. The boat actually lifts itself on plane before true hydrodynamic lift occurs. Once on plane, there is a teetering effect at the longitudinal center of gravity as you add or remove power. It is quite unusual, but not alarming in any way. Because so much of the boat is out of the water and it utilizes surface-piercing drives, it requires a little more directional attention; a characteristic of surface drives on a lightly loaded ship. In the case of the Axcell 65, once on plane with the mouse cages wound-up, there is not a lot of hull in the water to aid in straight line tracking, which can result in a bit of a squiggly wake. As the rooster tails blossoms at max speed, the hull is developing so much lift, coupled with a surface piercing drive, it leaves little surface and less appendage to aid in tracking.

She glories in a detail not often found in many yachts this size – retractable side windows. Great in aiding line of sight while docking, or simply ventilation...

Retractable aft windows can be set in any position. Here, we staggered the positions of the three aft windows...

A close-up aft deck shot illustrates the enormous space available at her stern swim platform. Sorry Bruce, we can't make this pic a hyperlink to the URL...

Nestled under the swim platform and stern is a tender garage with a 15' inflatable RIB...

This close-up study of her “Gills” is a graphic illustration of the creative thought and effort of inventor Barsumian’s essential performance secrets. His patented “HybridAir Technology is a product of those side “Gills”, where the blowers reside providing the necessary airflow to feed his new technological marvel.

A nighttime shot taken by YF photographer Tom Serio. Rope lighting behind the recesses draw attention to the Axcell's Air Pressure Lift system and why this boat deserves a closer look. <end>